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Author Topic: Would this work ?  (Read 212 times)

scott p

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Would this work ?
« on: December 25, 2021, 08:35:53 AM »
This bit From a recent post went unnoticed and the post moved on from the original subject. I am interested in this and decided to re-post.

The context here is the possibility of using several identical smart chargers to charge several batteries in series at the same time using a generator to power the chargers. This author gave his opinion.

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, 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

cobbadog

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Re: Would this work ?
« Reply #1 on: December 25, 2021, 10:41:30 AM »
Hi Eric and Merry Christmas, our day is almost completely over here and yours may well be jusssst starting.

Curious as to where you posted this before, was it in the geneartor section?

My view is that it is away over my head to be able to answer your very good question accurately. However I can tell you I have a simiar but a lot smaller issue that happens to me.
I own a beavertail truck for arting our tractor and other toys around to Rallies but due to covid the truck rarely gets used. It is a Hino with a 24v system (2 x 12v batteries). I get bogged down with work and neglect to start the truck on a regular basis so the batteries go flat after a few months which is expected.
I have 2 battery chargers, one old style 'el cheapo' that I connect to one battery and the other charger is a little bit more technically advanced as it is adjustable in the amps setting and can also be set to do a battery recondition over about a 24 hour period. This one I leave on 2amps which almost matches the other charger. I do NOT disconnect any cables when I put them on charge all I do is simply connect both chargers up first then power them both at the same time. This works fine in this situation for me. Not sure if this info helps but there are some very clever guys on this site and I have read threads on the generator section and there are some very clever 'sparkies' there too.
Something to consider is that we don't always log in and spend time reading the threads so sometimes it does take a bit of time to get replies. Something to try is to go to the generator section and read through some threds and find out which guys are offering help and try sending them a PM (personal messge) and ask for help with your problem and direct them to your thread.
Sorry I can't  be of any more help but stick with it and eventually you will have your answer.
Not wnting to take you away from from this Forum but there is another one that also maybe able to help which usually is somewhat busier than here. It is called Smokstak which is based in the USA. There is a lot of options to post there too for 'electrickery' work and guys who reverse engineer circuit boards FFS.
My appologies to Admin for mentioning another Forum and in no way putting down this Forum.
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scott p

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Re: Would this work ?
« Reply #2 on: December 25, 2021, 05:59:43 PM »
Hey cobbadog:
Sorry about the Eric thing He wrote it. I am just curious about it. Seems like a good practical way of keeping batteries healthy automatically when connected in series for off grid or electric cars.

The other post is in the everything else section, subtitle lead acid  battery confusion. I posted there also last night to fix a goofup on my part. The post mostly focused on keeping batteries healthy by attaching separate battery regulators to each battery and then monitoring those regulators according to each battery. 

Apparently I cluttered it up too much and this subject got lost.

BruceM

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Re: Would this work ?
« Reply #3 on: December 26, 2021, 01:10:19 AM »
I concur with Cobadog; as long as the smart battery charges (switching power supplies) are isolated type supplies, then yes, each can charge batteries that are connected in series. An isolated supply (aka transformer isolated) means it acts like a separate power source, like a separate battery.  It does not matter that the battery being charged may be at some elevated DC voltage relative to earth.

I use 3 smart chargers to charge my direct battery powered DC stick welder.  It uses 3 batteries in series, 2 are 12V, one 6V. The 6V is golf cart type, much larger capacity and a much higher (2A) float current.  The three smart chargers connect with the batteries still connected together in series.  It works fine.  It also trickle charges just fine on three small linear power supplies that I run whenever I've got my main battery bank inverter on.  Again, the trick being to have transformer isolated supplies so each can float to the right voltage level relative to the others.  Just for a thought experiment, if I was to take the welder ground cable, and connect that to the +120V battery bank, they will all still charge just the same as they would when either grounded at some point or floating (no earth reference at all).  This is a bit of a head bender, but if you work with transformers or batteries a lot you get used to it.  Some experimenting with small batteries and chargers on the bench will help.  Even if the battery is negative relative to ground, it works.  So "it's all relative" applies here.

You can also do the same thing with PV, though with lots of copper wire cost and some losses.  For example, you can charge four 12V batteries in series (48V) with four 12V PV panels, and 4 PV charge controllers.  The batteries could be different sizes and types, and as long as you don't use more amp hours than the smallest can safely handle, it will work fine.

With higher voltage strings, it becomes impractical to manage the number of charge current carrying wires and chargers.  The Rudman type shunt regulator design approach then becomes appealing since it lets you charge similar batteries in series with a single charger.

I hope this helps.

Best Wishes,
Bruce
« Last Edit: December 26, 2021, 01:13:21 AM by BruceM »

scott p

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Re: Would this work ?
« Reply #4 on: December 26, 2021, 02:00:11 AM »
All right then, thanks Bruce and cobbadog.
I was surprised see the diversity of this approach. I figured the variability of the system would need to be quite close.

I just finished a post on the other thread Bruce, feel free to ignore that.

cobbadog

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Re: Would this work ?
« Reply #5 on: December 26, 2021, 02:58:09 AM »
?Thanks Bruce for helping me out of the deep stuff. Electrickery is not my best subjuct and I on;y ever comment on what I have done without blowing myself up.
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scott p

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Re: Would this work ?
« Reply #6 on: December 26, 2021, 06:34:48 AM »
Hey Bruce::

A  battery powered DC stick welder ?

Are you able to vary the arc relative to the thickness of the metal you are welding and how is that done??

 scott

BruceM

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Re: Would this work ?
« Reply #7 on: December 26, 2021, 06:04:28 PM »
Yes, I adjust welding current with a massive strip resistor made from cut galvanized steel.   I use a big  gapped 1000W toroidal transformer core choke as an arc stabilizer, which helps greatly.

https://listerengine.com/smf/index.php?topic=8654.msg101247#msg101247

It works great in warm weather but in winter, the batteries output is a bit low and I'm running too cold a weld unless I warm them first.  In summer it will do 1/8 rods in 6013, or 3/32 7018. I can weld thin wall steel (1/16) with 1/16" diameter 6013 rods, but it is very tricky to maintain an arc and avoid burn through.

I'm interested in experimenting with TIG with the same gear,  but my health has been poor so I've put that on hold.  My though was that direct DC TIG with argon would be better for me- less fumes than the coated rods, assuming I can maintain a steady DC arc.   DC TIG welding of aluminum is possible with Helium.





« Last Edit: December 26, 2021, 06:43:49 PM by BruceM »

cobbadog

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Re: Would this work ?
« Reply #8 on: December 27, 2021, 03:24:17 AM »
Take care of your health first Bruce, apparently we only get one turn at getting it right.

I read about using batteries for DC welding on a welding Forum some time back plus using a good size alternator as another way of achieving it. The back story was this guy was going to a remote island in Indonesia somewhere and there was no power supply and he was building a fishing boat for the village to use. There was the issue of running a generator onsite becasue petrol was not easy to access so a diesel engine was to be sourced but there was not enough money for the village to buy it as yet as the same engine would go into the boat. It was like a dog chasing his tail this story but very good reading. It was a couple of years back now.
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