Lister Engine Forum
How to / DIY => Everything else => Topic started by: Tanman on December 16, 2021, 06:57:17 PM
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Hello, last year I built a 24v battery bank that consists of twelve 6v golf cart batteries. I have them in three strings of 4 batteries each. The problem I'm having is, the volts get pretty high pretty fast with a very low rate of charge (maybe 200 watts total). But it won't hold at this higher voltage. It will climb to 29 volts or so with only a few amps being applied. Also, the battery voltage seems to drop farily quickly with only small loads. Any idea why the batteries don't seem to have the umph they should have? They seem weak to me? Or are my charge controllers not doing their job?
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@Tanman
24V system here too.
With a bit different battery set-up, these are 2V 850 AH cells.
Charge voltage per factory spec:
Bulk and absorption.......29.7V
Float............................ 28.2V
Equalization...................31.8
My operating voltage is around24,8 plus or minus, that's when solar or generator charging is off.
The batteries have been in service for around 10 years.
I would think that Umph depends on what you loads are.
I operate a fridge, couple of freezers and a 3/4 HP deep well pump along with usual household loads.
Cheers
Hugh
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Batteries that recharge quickly and deplete rapidly, are generally sulphated..
12 GC2 batteries in a 24V config, would give you 24V @ 600ah. That bank would need 60A to properly charge. You might get by with 40A, and only using it very lightly.
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Hi Tanman,
I suggest a proper evaluation of all your individual cells via hygrometer, and also to check the batteries with digital voltmeter to find any batteries with bad cells. These are the most basic steps in evaluating your battery bank; checking for low cells with the hygrometer should be a periodic practice to assure that your equalization charges are adequate for balancing your cells. You cannot expect much battery life if you don't equalize often enough to keep the cells well matched by hygrometer. Cycle depth and rate of charge/discharge will affect the necessary equalization schedule.
You likely have killed some cells. As the old refrain goes; most batteries are murdered, few die from old age. Sulphation is the number one killer of lead acid batteries, but overcharging specific cells is a close second. This because as the batteries are charge/discharge cycled to some overall voltage level, the individual cells with the best performance get overcharged repeatedly, and those cells with the worst performance get undercharged repeatedly (and suphation forms in these specific cells).
If you find that you must replace your batteries, I'd recommend NOT having a bunch of 6V golf cart batteries in parallel. Get the capacity you need without parallel batteries, as Hugh has wisely done. Your savings account will thank me in time.
Parallel groups of cells accentuates divergence of individual 2V cell charge levels. It works fine while all the battery cells are closely matched but over time, it tends to kill batteries. If you replace an old battery with a new one, this insures very poor cell matching and will kill more batteries before their time. The strongest cells die by overcharge induced plate erosion, Weakest by sulphation since they never get fully charged.
I have lived off grid on lead acid batteries for 13 years now. Like most, I wish I'd done it sooner.
Best Wishes,
Bruce
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this site has the definitive last word on battery wiring schemes, and the math to go with it.
http://www.smartgauge.co.uk/batt_con.html
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Great article, Mike.
Alas, that article is not addressing the issue of parallel versus series batteries; it is only addressing the resistive wiring effects on battery current matching. That is certainly important, though not the only problem.
Even with perfectly matching currents, there is a small difference in charge/discharge capacity between cells which accumulates over time. You can see this readily with the hygrometer after a charge is complete. Low cells will eventually die if you don't use equalization charges long enough to bring them up. In doing so, you are shortening the life of the best cells by intentionally overcharging them; they will gas hydrogen and will be the cells needing more water.
WIth three strings of 4, 6V batteries connected together at the ends, being charged to a fixed voltage, this pretty much assures a problem and short life for the bank. I highly doubt this configuration would wire all 3 batteries in parallel because of the number of wires, though this would certainly help.
This problem was well documented by the early electric vehicle experimenters...even with all series batteries which have perfect current matching by design. They were using higher voltage AGM battery strings to get discharge current to reasonable levels and they were killing batteries fast. A guy named Rudman came up with an approach for what is now called a Battery Management System (BMS) which became a popular solution, they are a simple voltage (shunt) regulator used on every series battery. They prevent overvoltage at the battery level per charge cycle and reduce the need for regular equalization charges which AGM's can't handle well. I used this approach on my own 120VDC battery bank, and it accounts for the long life I get on cheap marine batteries. Within a few cycles, the batteries match so well there is less than a minute between then for charge completion. I have an LED current indicator on each battery regulator, so you can see when and how strongly the regulator is shunting current. I rarely have to use the hygrometer because of this...and am only adding about 1 gallon of distilled water once a year. I increase equalizations in year 4 to every 3 weeks. Because of the individual regulators, I can also replace any battery with a new one with the only penalty being a bit slower charge completion as charge current is restricted to 3 amps once the first battery is full.
The newer Lithium Iron Phosphate (aka LiFePO4 or LFP) batteries have cell level BMS; all parallel cells are directly strapped together and can be managed as one big cell, but each set of cells in series typically have a passive shunt voltage regulator (similar to the Rudman regulators), or an active balancer which is considerably more complex but does a similar job. They thus require no equalization of cells; the cell balancer hardware is doing that either all the time or whenever the cells are full depending on the cell balancer design (continuous vs top balancer). Continuous passive balancers are the most common; the highest voltage cells are discharged with 0.1 amp or more to bring them down to the level of the lowest cell. And yes, a failure of any cell balancer can wreck all those cells attached by over or undervoltage.
With lead acid batteries, not using a hygrometer periodically to see if your equalization charging schedule is adequate for the age of the batteries is a fast way to kill them young. It's the only way to see individual cell charge level as the internal cell connections aren't brought out to the battery exterior. A lead acid battery with each 2V cell terminals brought out for an electronic balancer would not require equalization and would also use less water; battery life would be improved greatly
It has always astonished me that even the high end PV systems have not adopted better battery management for their high end 48V systems. As if the batteries weren't the most expensive ongoing cost of the system.
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Very informative point of view from Bruce M, good piece of work, and the link supplied by mike is steller.
If I am reading correctly each battery has its own regulator. Your view seems to target AGM batteries but I would assume the BMS could be used with Flooded Lead Acid as well ? What do you think of this advertisement. It’s a quote.
(The Battery Balancer equalizes the state of charge of two series connected 12V batteries, or of several parallel strings of series connected batteries. When the charge voltage of a 24V battery system increases to more than 27V, the Battery Balancer will turn on and compare the voltage over the two series connected batteries. The Battery Balancer will draw a current of up to 1A from the battery (or parallel connected batteries) with the highest voltage. The resulting charge current differential will ensure that all batteries will converge to the same state of charge.)
You mention a 120-volt battery system, which I like because of lower current demands. Although I have not been able to source 120 volt AC inverters.
What about the sealed batteries that are taking over the standard battery market ? If the need to equalize is minimal why not use them. They claim to be immune to fluid loss.
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Hi Scott,
I think most should stick to standard 24/48V commercial inverter/charge regulator hardware, for service and support.
I had special needs and so I designed and built my 120VDC PV charge controller, BMS system and custom ultra low EMI inverter I think that even 48v is too low and I find the direct use of 120VDC for most electronics and some appliances and find ls quite handy. Nice for me and my neighbor but not a commercial product.
I use 10, 12V battery regulators for my 120V series string and they can shunt up to 3 amps. I use marine ''deep cycle'' lead-calcium type batteries because I get the performance I need from them and 5 years of service life on the latest ones at $90 each. I only add 1 gallon of distilled water annually for these; I love lead-calcium. AGMs would be about $235 each and might last 6-7 years. Both have float charge currents about 0.1 amp, unlike true deep cycle, wet lead acid batteries which eat an astonishing 2 amps at float and thus need regular watering. My custom BMS board watches the maximum and minimum shunt current feedback from each regulator and adjusts the demanded (PV or AC charger) charge current to my big linear charge regulator to satisfy the regulators. This assures that even if several batteries have failed with multiple cells shorted, no other batteries will be ruined by overvoltage. Battery regulation is also done for Equalization and Float. This allows a new battery to be inserted in the series string with the only penalty being slower charging for the last bit of charge, since charge current will be limited by the new batteries regulator feedback at the "most I can handle" rate (of 3 amps).
A 1 amp battery shunt regulator will certainly help keep the batteries matched and lessens the need for equalization, but they would not stop a runaway situation where several cells have shorted, and PV capacity is relatively large. it will always help to some extent, and will lessen the problem somewhat. I would prefer to see some sort of battery level overvoltage shut down of charging. And perhaps these do have something like that.
AGM batteries are great, just priced too high for the small improvement over wet lead acid except in some situations where higher current, higher efficiency is needed. Using battery regulators on AGM batteries would be a must, in my mind. But for that kind of money, today I'd look closely at some of the new cheaper server rack LFP batteries or an assemble my own setup with prismatic LFP cells and a high qualty BMS/passive cell balancer.
Best Wishes,
Bruce
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I tested all the cells with a hydrometer, they all are pretty much the same at around 2.25v per cell. There were no very low or high cells. So I’m guessing my charge controllers (2 inexpensive 30a mppt charge controllers) do not have the proper settings to get the bank fully charged. And unfortunately they are not adjustable. My plan is to ditch these for a higher quality unit and see how that goes. The factory set float charge on the controllers I have is 27.5v
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That must have been very welcome news.Glad to hear you sorted it out because it sure enough pointed to shorted cells and thanks for giving us a chance too hear from Bruce.
I ran across a bit of information that seemed to be worth mentioning. The idea is to run large capacitors in parallel with each battery. The effect being they help smooth out sudden high current loads thereby extending the overall health of the battery bank.
I have often thought about converting my shop to 120 volt DC. just for the experience of learning the ins and outs of battery power. I get a lot of raised eyebrows when I mention I have a 120 volt DC to 120/220 volt AC motor generator set I would more than likely use to start with since the shop would often be idle with no AC load and why could it not be used similar to a startomatic situation.
As long as light bulbs have the right volts they don't care and I imagine there are DC heaters. It would be nice to be able to build those nice Rudman type regulators.
This a hypothetical thought experiment at this point but on rare occurrences I have found that what seems wrong to begin with turns out to OK in the end.
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Hi Tanman,
You wrote that your tested with a hydrometer yet you listed 2.4V. Hydrometers measure specific gravity of the acid solution, which gives you a per cell state of charge. So you may have misunderstood what I was asking for. The units on my hydrometer gives 1100 for low charge, 1350 for full. I don't recall the units off the top of my head.
If your batteries are reading 2.4V for a 6 volt battery, you have likely killed them. There is no way to measure cell voltage for most golf cart batteries. So that 2.4 doesn't make sense for battery voltage either.
You would have to disconnect the parallel connections to compare individual battery voltages.
So I'm stumped as to what is going on from what you have reported. You previously reported battery voltage going to full voltage very quickly, which is not consistent with a PV controller failure. So it seems you might be best off getting some competent help to look things over and give you some instruction, and/or retry your hydrometer and voltage measurements.
Hi Scott,
Since a battery is also inherently a large capacitor, I see no value in putting a capacitor across each battery for the stated purpose. I don't believe that the lead acid batteries will be harmed by current surges withing the limits of their design currents. Most inverters have bulk capacitance at the battery inputs already, so current peaks will not be seen by the battery.
One important thing to remember about 120VDC is that high voltages can kill. DC is 4x safer than AC at the same voltage. It feels like a static shock instead of the pain of 120VAC. But caution is still warranted. 120VDC will maintain a arc, so arc hazzard is greater than AC.
Most switches designed for AC will fail via arc and melt down with the first opening of the contacts. The reason is that AC self extinguishes any arc within 8.3 milliseconds, when the current goes to zero, so no means of arc breaking is required. Contacts thus only need open every so slightly for AC. For DC, a faster snap action that opens the gap quickly, sometimes even bending the arc via magnets is used. The Leviton (and most others that copied their design) rotary lamp switches, and the rotary lamp cord switches will work fine on DC, because they were designed for Edison's early DC power, and the design has never been changed. There are a few 150V DC, lower amp rated switches (4A) you can find at Digikey. One day I tested and ruined 6 different brands heavy duty AC wall switches for compatibility, all failed on the very first opening while controlling a 4 amp resistive load. It was a few hundred dollars up in smoke in 15 minutes. Cooper once made a 150VDC rated duplex wall switch but that model is now discontinued.
This applies to appliance switches, also. My blender has the switch removed- just as in the early Edison days, you turn on the appliance by plugging it in. Ditto for my heat gun/hair dryers- I tape wrap the switch on to avoid a fire hazard. Crock pots are fine, but you have to remember to only change the heat setting (element selection) by unplugging first. Devises with duty cycle thermostats (bimetal current sensing duty cycle switches) will NOT work on 120VDC without new solid state duty cycle switching control. Oddly, some of the cheap kitchen motor tools like a Hamilton Beach stick blender and a small coffee grinder work just fine on DC, EVEN THE SWITCH. This is likely because the brushed universal motor design on these generates enough back EMF on opening the commutator that current briefly goes through zero and stops the arc. Its a fluke of design I check for but is rare.
Best Wishes,
Bruce
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This whole battery thing has got me all wired up. Found this on a EV sight.
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Zener-lamp regulator////
Lee Hart wrote on 2/26/03:
Here is a design I have been playing with for about a year. I have two working systems installed, and while not as aggressive as a full-blown Battery Management System, it does most of the job and at very low cost.
Battery regulators
Here is the wiring diagram of the battery regulators:
Battery -
5/16" 6 gauge
ring terminal
______________
| \ __ \
_______________|/|__\ / \ |
Battery + | |\| / \__/ |
5/16" 6 gauge ____|__ | __|____ |_____/________/
ring terminal / | |_|_| | \
______________ \____|__| |__|____/ zener diode
/ __ / | | | | | 1N5338B
| / \ /__|/|_____________|_____| 5.1v 5w
| \__/ \ |\|
\________\_____| 2 lamps in parallel
each #PR2
Charge Current Limiter
One simple way to force a charger to limit its output current is to put some resistance in series with its output. A light bulb is a good way to do this, because it acts like a crude constant-current source. The current only changes about 2:1 for a 10:1 change in voltage. For example, an ordinary 120vac 150w light bulb draws 150w / 120v = 1.25 amps at 120v, and about half this or 0.625 amps at 12v.
Wiring diagram:
lamp
120v 150w
__
__/ \__
| \__/ |
| |
charger+__________|___||/__|__________battery+
COM1 /|| NC1
______
hot________| |
| |____
120 | | _| relay
vac | | _| 120vac
| |____| coil
neutral____| |
|______|
children's "night light"
(turns light on in darkness)
Parts list:
1 - 120v 150 watt light bulb and socket (choose wattage for desired limiting current)
1 - relay, SPDT contacts to match charger max amps and volts, 120vac coil (for example, Potter & Brumfield T92 series, DPDT 30a 240vac contacts, 120vac coil, Mouser 655-T92P11A22-120, $10.50)
1 - children's night light with photocell that turns it off when it senses light. Replace its lamp with the relay coil
Locate the night light inside the battery box where its photocell gets exposed to light from any of the battery sensors. When no light is detected, the relay coil is off, so its normally-closed contacts short the light bulb and the charger delivers full power to the batteries. When the first battery regulator lights, it pulls in the relay, which opens the contacts and puts the light bulb in series with the charger, limiting its current.
Usage
Add my zener lamp regulators across each battery.
Add a timer to turn off the charger after a set time. I like the Intermatic mechanical timers that you can set for 0-12 hours with a knob; they count down and turn off ($15-$20).
Next time you charge, watch the lamps on the regulators. When the first one comes on, set the timer to only run another hour or so. If the pack is out of balance, you'll probably find that after an hour, only a few lamps are on.
Do the same thing for the next few charge cycles. Each time, you'll find that more lamps will be on after that final 1 hour of charging, as the batteries get pushed closer to balance. After a while, the last lamp should just be starting to light at the end.
If you have a fairly consistent driving cycle (say 10 amphours/day), you'll find you can set the timer for a specific time (like 5 hours) right at the beginning, and will automatically get that 1 hour extra charging time after the regulators light up.
If your cycle isn't that consistent, you'll have to figure out by trial and error how much charge time to select for each depth of discharge.
You can automate this process by adding a light sensor and high/low relay.
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I'm working on my first EV conversion, and am wondering if anyone knows of where I could find a good balancer/equalizer BMS for flooded lead acid batteries. It is for a 96 volt pak.
Alternatively, you can look into multiple-bank chargers. Dual Pro makes a 4 by 15A charger that operates as 4 separate 12v smart chargers. Your 96V system would need two of these chargers. These chargers are connected to each 12V battery (or each pair of 6V) and do their charging without having to separate the pack. The electric boat people are very pleased with how this is working and many are switching back from bigger 48V chargers. The Dual Pro is basically a 900W charger
Pro-Mariner makes a 30A charger that will manage 4 different batteries. This charger has the ability to shift amperage to the neediest battery, effectively allowing for 30A of 12v charging if only 1 out of 4 batteries is low, but since the batteries are connected in a pack, that type of unbalance is unlikely. The ProMariner is essentially a 450W charger. These are around $600
That said, I'm using a 48V Elcon 2000+ with EV Works BMS modules for my lithium pack.
I've also seen some people suggest separate small, inexpensive 12V chargers for each battery. This will perform the same type of balancing as BMS or multi-bank chargers.
Eric
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I have seen this too. How does one go about isolating each individual battery for this?
most of the newer smart chargers are isolated...note the most not all.
You don't have to isolate the batteries when charging, as long as the entire bank is being charged at once.
You can imagine that applying a single 12V charger to part of your battery pack will never complete charging the battery that it is hooked up to because the other batteries that are not charging would be adding load. In this situation, the hooked up battery would be taking considerable abuse by having all the current flowing through it to the other discharged batteries.
But if you had a separate 12V charger attached to each battery, charging all at once, each battery has enough autonomy, even while wired in series, to allow the charger to select the charging phase according to that battery's needs. So the first battery to the constant current cutoff would start the constant voltage phase with decreasing amps, even while it's neighbor was getting still taking full amps. You won't get much cross battery flow since they are all in a charging phase and should be close to the same voltage. Once all the batteries get to the constant voltage phase, there won't be any cross flow, because there is no voltage difference. As each charger drops into the float phase, reduced voltage and amps, there will be some minor cross flow, but since the amps are down across the entire pack, the amount of current flow should be negligible. As long as one charger is pushing current, all of the batteries would stay at a higher than resting voltage, but not really getting any more charge. Once the last charger shut off, the whole pack would return to it's resting voltage.
While there is some room for a massively out-of-balance battery to confuse some of the chargers, this strategy will keep the batteries top balanced by tailoring the charge to each battery, so a dramatically out-of-balance situation would be rare. If you noticed that one charger ran consistently longer than the others, it would indicate a failing cell. This is similar to noting that one battery never hit peak voltage and starting shunting with BMS.
This is why the multi-bank chargers, hooked up to individual batteries that are connected in series (like ours) or parallel (house batteries in RV's and boats) work so well in keeping the batteries in balance.
Eric
Well Eric, have you tried it, this sounds too good to be true but worth investigating I priced some smart chargers as low as 40$.
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Flooded batteries do not need Equalizers. After 3-stage charging, you finish with an equalizing charge of 3 to 5 amps for a few hours. This bubbles the electrolyte and is a way of dissipating energy as ALL the cells come up to full charge.
The ZIVAN NG3 does ALL this and is isolated.
I have an order out for 9 PowerCheq modules for my 120V pack. Another forum user DONEAL has had success with these balancers (11 of them) for his 144V pack. I'll let you know how they work when I get them. I asked DONEAL how they were working and he said great.
I have a single charger for my 10 AGMs and they get out of balance very quickly.
I don't think most people bother with a BMS on a pack of floodies.... if one goes over-voltage at the end of the cycle, it would just gas a little until others caught up.
Dan
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more people now days are using lithium batteries because of its various advantages. but lead acid batteries are much cheaper. and generally no need BMS.
maybe you can try to use lithium battery pack +BMS+charger
or lead acid battery+elcon charger
elcon charger has high efficiency and overall protection functions.
we can offer this charger to you at very good price.
Email:sales.wicom@gmail.com
Skype:sales.evparts
supply lifepo4 batteries+BMS+charger
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I'm not sure I would use an equalizer on floodies, but if you AGM/sealed batteries... I wouldn't run without them. I bought these.... awesome....
http://www.hdm-sys.com/pdf/hdm_equalizer_specs.pdf
I have 5 of them on a 192 volt pack. Equalize 5 amps during charge, discharge and idle. I've even heard of them used with mixed batteries.
Shiva.
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I don't think most people bother with a BMS on a pack of floodies.... if one goes over-voltage at the end of the cycle, it would just gas a little until others caught up.
I did this on my pack of 24 6V batteries and ran them for nearly 9000 miles. A charger that will do an equalization charge is all you need. I have a Zivan NG5 that I used. The end charge was about 181V or 7.54V for a 6V battery. It just wastes a lot of power doing so but so would a BMS I suspect.
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MK3SMT Digital Lead Acid Regulator ::: One for each battery, ManzanitaMicro.com, very fancy, lots of cool state of the art digital monitoring stuff $125 each.
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Too much for me to sort through, but I will comment that Manzanitapower.com once had a detailed article describing their earlier, non-digital Rudman Regulators which helped me greatly in the design of my own design for PV charging. PV charging is a bit trickier as PV input can vary widely in time with changes in weather as you are charging. Their digital design uses a digital controller which talks to the batter regulator bus and which throttles the charge current. It was not designed to be used with a PV charge regulator, and you'd have to contact them regarding that application.
A 5W zener for top balancing of LA batteries seems a popular among people who haven't competence electronics design. Its not enough current capacity for all conditions and battery ages. You can simulate a much larger zener easily with an op amp IC, power transistor and a power resistor...and it can easily regulate at a temperature compensated voltage at bulk, float and equalize. I've attached my own design which is pretty dated in components but still works fine.
The role of battery balancers in LA batteries is to reduce the frequency and time needed for equalization. It is essential for sealed or AGM batteries, and for wet LA it extends battery life, as equalizations eat the battery plates over time.
The true deep cycle LA batteries such as forklift or the some large 2V cells are designed for high current charging and their care and life extension is outside my hands on experience. They may require more regular equalization for other reasons than just cell balancing...like stirring the electrolyte, plate surface maintenance, etc. I just don't know.
I really expected to be using AGM batteries by now but the prices are just not competitive for my application compared to the lead-calcium, "marine" batteries I started with as a cost saving measure for my prototype hardware testing. I only paid about $600 for my first set of 10. At that time AGMs of the non-true deep cycle type would have been over $2500.
A Johnson Controls battery engineer I talked with suggested I would likely only get 1 year out of their marine batteries in my application. A propane refrigerator (lower DOD) and battery regulators upped that to 5 years.
Bruce
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Bruce,
Although I struggle to understand some of your details your knowledge on these off grid systems never ceases to amaze me.
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Thanks Butch. Most folks moving off grid kill their $5-7K starter battery bank in a year or two, then wise up and manage their night power use, and often increase their battery bank and PV size. Expensive lessons stick in the mind. Even non-technically inclined seem to catch on pretty well. Today is a very dark day, so Ill be cooking with propane as the PV struggles to top up the batteries (134V and slowly climbing during some thinner clouds).
Lithium iron phosphate batteries will likely become economical for home power in the near future, and that will end most discussions of the care and feeding of wet lead acid batteries.
The BMS or battery management systems with cell balancers that are required for lithium (LFP) batteries will take care of them quite well and should last as long as new fork lift batteries but with much higher charge efficiency and much lower self discharge rate.
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re: what you said about people killing battery banks,,
Off this topic but I watch a few of the build off grid shows on TV and most of the time they give an account of what the system will provide. Then seeing how some of those home builders act (as in not self reliant and mechanically ignorant) I can't help but to think to myself, you two are in for a few surprises. LOL
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It's a lot easier to adjust to a PV - battery system than most realize. For me its as simple as checking the sky in the morning to know if it's a good day for laundry and electric cooking. I have a low DOD, batteries must be topped up every day policy.
The Lister(oid) CS makes a great backup generator. I may have to do some battery bank charging this coming week of clouds and rain. I've not run the Lister for battery charging the last few winters thanks to the now 2400W of PV. It's slower than sunny days but unless very dark I get enough.
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The Lister(oid) CS makes a great backup generator. I may have to do some battery bank charging this coming week of clouds and rain. I've not run the Lister for battery charging the last few winters thanks to the now 2400W of PV. It's slower than sunny days but unless very dark I get enough.
I'm 2 weeks into daily cloudy weather, many days, not even a kwh of solar harvest. I think I've burned more diesel in the last month, than I have in the last 3 years. And another week of clouds, and 1 day of partial sun ( maybe )
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The Lister(oid) CS makes a great backup generator. I may have to do some battery bank charging this coming week of clouds and rain. I've not run the Lister for battery charging the last few winters thanks to the now 2400W of PV. It's slower than sunny days but unless very dark I get enough.
I'm 2 weeks into daily cloudy weather, many days, not even a kwh of solar harvest. I think I've burned more diesel in the last month, than I have in the last 3 years. And another week of clouds, and 1 day of partial sun ( maybe )
Mike, we must be getting all your sun here in Ohio. Sunny every day this week which is very unusual weather for us this time of year. usually very gloomy
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Mike, that sure is a brutal forecast for PV power. I'm spoiled for sun here in AZ, most winters.
Around 1990 -2010 most off grid folks here used a mix of PV and wind, often with much more wind power than PV. Back in those days trackers were common since PV was so expensive.
I can usually get enough charge via PV unless it is very dark all day.
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I see the post has moved on to other subjects but I noticed the do it yourself zener battery-lamp bit I posted was gibberish so I will post it as an attachment in case someone for whatever reason wants to look at it.
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Hi Scott,
I stand corrected.
In the attachment I see the method of reducing charge current to less than 1 amp via insertion of a 150W bulb in series, triggered by a 120VAC powered night light sensor to switch in a 150W light bulb in series with the DC charging to limit current when a battery regulator is lighting up. For higher DC voltages this least expensive via a solid state, DC relay or a low side MOSFET switch triggered by a photodetector in this case. They have two 5V, 5W zeners in series on each 12V regulator, which increases doubles the shunt current capacity to 10W, with the lamps acting as both current indicator and current limiter. Crude but effective. If you wanted this to work with the inverter is off or fails, then an alternate circuit for light detection should be used. It is a rather novel means of opto isolation without using an opto isolator IC.
The light level to trigger the night light will be critical, and it is an all or nothing switch to very low charge current, which will cause an on/off oscillation when there is a load say half the PV capacity being applied while charging, but for a simple demo it will work, with some care about stray light and visibility of each regulators light to the night light.
This is the essence of how the Rudman type battery shunt regulators work- the regulator signals for current reduction when the battery is being regulated.
I hope Tanman will accept my apology for highjacking his thread, and I hope he gets his battery situation sorted out.
Best Wishes.
Bruce
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hello Bruce::
Hijacked or not a ton of information came out of it thanks to tanman.
Don't know if Tanman is still around but I was thinking, in order to perhaps salvage some batteries he could do a resistive load test with a rough look at the amp hour rating relative to the resistance of the resister . A hot water tank element or something with decent resistance.
On a personnel level (sorry tanman) I am most curious what your opinion would be on the following bit that was buried in my post. It seems like this approach would be a kind of stand alone super regulator that anyone along with some pocket change could use even with a plain generator.I would us identical smart chargers.
POSTED BY ERIC AND A COUPLE OTHERS
I've also seen some people suggest separate small, inexpensive 12V chargers for each battery. This will perform the same type of balancing as BMS or multi-bank chargers.
I have seen this too. How does one go about isolating each individual battery for this?
most of the newer smart chargers are isolated...note the most not all.
You don't have to isolate the batteries when charging, as long as the entire bank is being charged at once.
You can imagine that applying a single 12V charger to part of your battery pack will never complete charging the battery that it is hooked up to because the other batteries that are not charging would be adding load. In this situation, the hooked up battery would be taking considerable abuse by having all the current flowing through it to the other discharged batteries.
But if you had a separate 12V charger attached to each battery, charging all at once, each battery has enough autonomy(independent of other batteries), even while wired in series, to allow the charger to select the charging phase according to that battery's needs. So the first battery to the constant current cutoff would start the constant voltage phase with decreasing amps, even while it's neighbor was still taking full amps. You won't get much cross battery flow since they are all in a charging phase and should be close to the same voltage. Once all the batteries get to the constant voltage phase, there won't be any cross flow, because there is no voltage difference. As each charger drops into the float phase, reduced voltage and amps, there will be some minor cross flow, but since the amps are down across the entire pack, the amount of current flow should be negligible. As long as one charger is pushing current, all of the batteries would stay at a higher than resting voltage, but not really getting any more charge. Once the last charger shut off, the whole pack would return to it's resting voltage.
While there is some room for a massively out-of-balance battery to confuse some of the chargers, this strategy will keep the batteries top balanced by tailoring the charge to each battery, so a dramatically out-of-balance situation would be rare. If you noticed that one charger ran consistantly longer than the others, it would indicate a failing cell. This is similar to noting that one battery never hit peak voltage and starting shunting with BMS.
This is why the multi-bank chargers, hooked up to individual batteries that are connected in series (like ours) or parallel (house batteries in RV's and boats) work so well in keeping the batteries in balance.
Eric
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I don’t mind the Segway, interesting things all the way around. My bank is still under warranty, so I’m just going to return it. I hardly used it and it’s having serious trouble holding a charge. I’m going to go find larger amp hour deep cycle batteries instead of these.
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Okay, so I returned my bank. They weren’t really happy about it, but processed it lol. I also recently discovered that a local auto place sells lithium ion ev car batteries that have been removed from crashed cars. They are selling a Prius Prime 8.8kwh pack for around $1450! (I can go pick it up with my truck) The vehicle only had 12,000 miles on it! This seems like the way to go.
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Hi Tanman,
I'm not familiar with the Prius Plus battery packs and their BMS, but note that they are high voltage (>200V) batteries that could not be directly used with standard off grid 24 or 48V input inverters and PV charge regulators.
Have you found a home power system that is directly compatible and interfaces to the BMS system so you can monitor battery pack health and balance? Rebuilding a new battery with the old cells to make a lower voltage battery with a new BMS would be possible but is a significant technical effort.
Lithium Iron Phosphate batteries are more appealing to me due to much better fire safety. There are some server rack LFP battery systems that are more home power system suitable; they have a built in BMS and are directly compatible with 24 or 48V input inverters and PV charge regulators.
Best Wishes,
Bruce
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So the nominal voltage of each cell in the prime pack is 3.7 volts, so 13 of them would put me at a 48.1 nominal voltage. I’ve also seen some guys run them without bms, they just put low amp fuses on each string and keep an eye on them.
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Reconfiguring the cells for a 24V or 48V setup should be an interesting project. I look forward to seeing your progress!
There are some decent, inexpensive add on BMS/balancer systems available. I'd suggest doing that. Cheap insurance since the Lithium ion cells are ruined permanently with over/undervoltage. The BMS would disconnect charging on single cell overvoltage, disconnect load with single cell undervoltage. Important for fire protection as well.
One gotcha to avoid;if you use a cheap MPPT PV regulator that is buck converting from a high voltage PV array, it is wise to use either a BMS with voltage rating above the PV voltage, or add an overvoltage crowbar or disconnect to prevent a failed PV regulator from connecting the PV high voltage to the battery's BMS. The MOSFETs in the PV regulator normally fail shorted from input to output, and in a buck converter that means it's a full on. This causes an overvoltage failure, full on short of the BMS overvoltage disconnect so full PV power was connected to the battery. This is not conjecture on my part, but a reported failure including photos, with a brand new lithium pack worth over $5K destroyed. The alternative solution is to limit PV voltage to the rated max voltage of the BMS disconnect.