Author Topic: Lead acid battery bank confusion  (Read 1864 times)

38ac

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Re: Lead acid battery bank confusion
« Reply #15 on: December 23, 2021, 09:33:09 PM »
 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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BruceM

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Re: Lead acid battery bank confusion
« Reply #16 on: December 24, 2021, 02:54:31 AM »
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.



mike90045

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Re: Lead acid battery bank confusion
« Reply #17 on: December 24, 2021, 06:40:27 AM »
.....
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 )

38ac

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Re: Lead acid battery bank confusion
« Reply #18 on: December 24, 2021, 01:44:39 PM »
.....
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
« Last Edit: December 24, 2021, 01:46:54 PM by 38ac »
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BruceM

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Re: Lead acid battery bank confusion
« Reply #19 on: December 24, 2021, 03:22:40 PM »
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.


scott p

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Re: Lead acid battery bank confusion
« Reply #20 on: December 25, 2021, 08:13:51 AM »
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.

BruceM

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Re: Lead acid battery bank confusion
« Reply #21 on: December 25, 2021, 06:38:56 PM »
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






« Last Edit: December 25, 2021, 06:41:44 PM by BruceM »

scott p

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Re: Lead acid battery bank confusion
« Reply #22 on: December 26, 2021, 01:12:38 AM »
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

Tanman

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Re: Lead acid battery bank confusion
« Reply #23 on: January 02, 2022, 01:16:25 AM »
I donít mind the Segway, interesting things all the way around. My bank is still under warranty, so Iím just going to return it. I hardly used it and itís having serious trouble holding a charge. Iím going to go find larger amp hour deep cycle batteries instead of these.
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Tanman

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Re: Lead acid battery bank confusion
« Reply #24 on: January 07, 2022, 06:15:46 AM »
Okay, so I returned my bank. They werenít 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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BruceM

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Re: Lead acid battery bank confusion
« Reply #25 on: January 07, 2022, 05:23:33 PM »
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





Tanman

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Re: Lead acid battery bank confusion
« Reply #26 on: January 08, 2022, 10:17:42 PM »
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. Iíve 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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BruceM

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Re: Lead acid battery bank confusion
« Reply #27 on: January 09, 2022, 12:26:26 AM »
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.