Help Sizing Charger

MambaJack · 02-26-2019, 11:09 AM

So i jumped the gun last fall and purchased 8 215 ah fla batteries for the bus, but just now getting around to buying something to charge them from shore.

Looking for advice on best charging them. Currently looking at a a Progressive Dynamics 24v 40amp charger. Is that enough?

I have some 12v dc stuff and some 110ac (fridge, tv) that i plan eventually to get an inverter for.

Also am thinking of a manual switch or plug to change from inverter to shore.

Thoughts?

MambaJack · 02-26-2019, 11:10 AM

I do plan to add solar eventually which is why i am thinking a 24v bank might be best and downconvert for my 12v stuff

PNW_Steve · 02-26-2019, 11:48 AM

Well.....

FLA like to be charged at C/8-C/12. A good rule of thumb is 10% of your batterys C20 rate.

What is the voltage of your batterys? You gave us. Amp-hour rating but not voltage.

Some good battery info:

https://www.solarpaneltalk.com/forum...your-batteries

https://www.solarpaneltalk.com/forum...tteries-part-2

MambaJack · 02-26-2019, 11:57 AM

Sorry, they are 6v golf cart batteries

MambaJack · 02-26-2019, 12:16 PM

So 8 6v 215ah batteries comes to a bank of
24v 430ah

10% of 430 is 43amps recommended, the charger i am looking at is 24v 40amp

is this close enough?

PNW_Steve · 02-26-2019, 12:19 PM

Eight GC2's in series will yield a 48 volt / 215 amp-hour battery.

If you want to go 24volt, I would recommend four L-16 batteries in series. That will yield a 24 volt / 400 amp-hour battery.

A good starting point would be 10% of the C20 rate. The charger that you linked appears to be adequate.

MambaJack · 02-26-2019, 12:32 PM

I already have the batteries, is it bad to go 24v series parallel then?

ol trunt · 02-26-2019, 12:39 PM

I'm using the progressive dynamics 9245C to charge my 12v GC batteries. I managed to get 7 years out of my batteries before I began to notice any decline in their service. I've been careful not to let the batteries go low on water and not to over discharge them. Also, I installed the "pendant" which allows me to see what charge rate is being applied as well as to select a rate. There are several good charger/converters on the market so give them all a look.
Jack

john61ct · 02-26-2019, 01:20 PM

The default should be 12V unless you have compelling reasons to go any higher.

What you might save in thinner wire gets eaten up by higher costs in all the ancillary gear, especially load devices, high-current buck converters aren't cheap.

IMO

PNW_Steve · 02-26-2019, 01:36 PM

Quote:

Originally Posted by MambaJack

I already have the batteries, is it bad to go 24v series parallel then?

Not all batteries are exactly the same. Internal resistance can vary enough that some of the batteries in the parallel string will "do more of the work" than others. They can also charge at slightly different rates. This can lead to premature battery failure.

There is a lot of good solar, battery and charging info in the stickies on www.solarpaneltalk.com.

Learning from others mistakes costs a lot less than learning from your own

PNW_Steve · 02-26-2019, 01:39 PM

From http://www.smartgauge.co.uk/batt_con.html
I wouldn't be surprised if a large number of installations are wired like this. The problem is that this configuration can lead to the current in the last battery in the chain being around half the current in the first battery! This problem is easily fixed by following the guidelines from Smartgauge.

If the batteries all have different internal impedance/resistance even if the wiring is done correctly the batteries will not share the current evenly. The battery with the highest impedance/resistance will draw or supply the least current. Is this a problem? Surely the weakest cell should be pampered, if it supplying less of the load I would think it would deteriorate at a slower rate to the other batteries. This would be a self balancing mechanism.

The second issue is only a problem with LA batteries. All LA batteries need enough "absorb time" to make sure the battery is fully charged to stop sulphation but extended time at high charge voltages reduces their lifespan. This problem cannot be eliminated but can be minimised by making sure that all the batteries being paralleled are the same age (preferably new), have the same history and are the same make and model and preferably from the same manufactured batch. I think the same problem occurs with LA cells or batteries in series.

Regardless of battery chemistry if there is a mismatch in battery impedance/resistance the cells/batteries with the higher impedance/resistance will charge or discharge at a slower rate which will mean that regardless of battery chemistry unless there is some "absorb time" the cells/batteries will not be at the same SOC.

MambaJack · 02-26-2019, 01:57 PM

Quote:

Originally Posted by john61ct

The default should be 12V unless you have compelling reasons to go any higher.

What you might save in thinner wire gets eaten up by higher costs in all the ancillary gear, especially load devices, high-current buck converters aren't cheap.

IMO

I have actually spent quite a bit of time trying to figure out the right path on the solar panel forum, and have got a little bit conflicting answers. I would love to go 12v, but from my understanding that worsens the ability for a equal charge across the bank to have 4 sets in parallel of 2 in series vs 2 sets of parallel with 4 in series,

plus when i get to solar later, it might mean
a more expensive charge controller

MambaJack · 02-26-2019, 02:00 PM

Quote:

Originally Posted by PNW_Steve

From SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank
I wouldn't be surprised if a large number of installations are wired like this. The problem is that this configuration can lead to the current in the last battery in the chain being around half the current in the first battery! This problem is easily fixed by following the guidelines from Smartgauge.

If the batteries all have different internal impedance/resistance even if the wiring is done correctly the batteries will not share the current evenly. The battery with the highest impedance/resistance will draw or supply the least current. Is this a problem? Surely the weakest cell should be pampered, if it supplying less of the load I would think it would deteriorate at a slower rate to the other batteries. This would be a self balancing mechanism.

The second issue is only a problem with LA batteries. All LA batteries need enough "absorb time" to make sure the battery is fully charged to stop sulphation but extended time at high charge voltages reduces their lifespan. This problem cannot be eliminated but can be minimised by making sure that all the batteries being paralleled are the same age (preferably new), have the same history and are the same make and model and preferably from the same manufactured batch. I think the same problem occurs with LA cells or batteries in series.

Regardless of battery chemistry if there is a mismatch in battery impedance/resistance the cells/batteries with the higher impedance/resistance will charge or discharge at a slower rate which will mean that regardless of battery chemistry unless there is some "absorb time" the cells/batteries will not be at the same SOC.

Thanks Steve!

I have seen this article before. Is your impression that if I use the recommended way of wiring it eliviates the issue of equal charging to different batteries in the bank? If so, i might consider going back down to a 12v bank with 4 sets or 2 6v batteries wired in parallel.

john61ct · 02-26-2019, 04:08 PM

Quote:

Originally Posted by MambaJack

I have actually spent quite a bit of time trying to figure out the right path on the solar panel forum, and have got a little bit conflicting answers. I would love to go 12v, but from my understanding that worsens the ability for a equal charge across the bank to have 4 sets in parallel of 2 in series vs 2 sets of parallel with 4 in series,

plus when i get to solar later, it might mean

a more expensive charge controller

bollocks

Just avoid too much paralleling by going to bigger cell size as the bank size grows.

2V cells @1000+ Ah are available if needed, may be pricier than cheap GCs, but then good ones last much longer if treated well.

Many people use 4 strings, personally I would do 3 maximum.

PNW_Steve · 02-27-2019, 04:09 PM

Quote:

Originally Posted by MambaJack

Thanks Steve!

I have seen this article before. Is your impression that if I use the recommended way of wiring it eliviates the issue of equal charging to different batteries in the bank? If so, i might consider going back down to a 12v bank with 4 sets or 2 6v batteries wired in parallel.

I think that it is better than the alternatives.

It helps but does not address the challenges caused by varying internal resistance inside the batteries.

john61ct · 02-27-2019, 04:26 PM

If you buy quality deep cycle batteries from the half-dozen known good makers, install and care from them correctly, an 8-12 years' bank lifespan is entirely do-able.

Even if you cheap out or don't learn how from the beginning, 3-4 years is still likely.

This stuff is not rocket science at all.

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