# batteries, series-parallel, balancing, help me understand

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Hi guys, this is my first post, I have been collecting parts for my solar system and studying at the university of Google for quite some time now, but I have a few questions about my first setup. I don't have any previous solar experience but I have a pretty strong electrical background as I have been wiring things since I was small and have made a living working on overpriced/overly complex European vehicles for the last 10 years.

I specialize in automotive electrical diagnosis and do complex rewires/engine/computer swaps on the side. So I can normally spot when someone knows what they are talking about with electrical, and those that don't, and let me tell you, this site is the best as far as giving good, correct, safe info. There are a lot of experts here, which is why I decided to join.

In cars you almost always deal with just one battery, sometimes two in parallel, so balancing is never a consideration, but what I don't understand is how do many batteries in a parallel string get unbalanced? I mean if they all are connected and charged the same, I figured that the weaker batteries would just put out less as the SOC dropped and as long as they all when through the absorb part of the charging cycle then each battery would "take" what it needed to fully charge. Obviously I am incorrect, but not sure why.

I initially was going to go with a 12v system and a large AH bank of 12v batteries, but I found a great deal on a victron energy multiplus 24v inverter and found out the many other benefits of going 24v(double capacity of CC, smaller cables,etc.) so I am going 24v.

I'm also studying up on building an electric vehicle, I plan on building one after the RE project is done, I notice they have large high voltage strings of batteries in series, since the charger only sees the total voltage, it can overcharge the good batteries while the weaker ones are still charging. Some times with lead and almost always with lithium they use a little dump load(balancer) on each battery that shunts some of the charging current on individual batteries as they reach their maximum voltage.

I have 12 12v 100AH agm's, I guess I am going to use the diagram I see most for my 24v system, making 6 24v strings of two batteries and paralleling them all together. But doesn't this give more chances to get unbalanced batteries than if I make two 12v battery banks and series them together? Could someone explain how this works and why I am wrong? Would little mini balancers on each battery help?

I have a 12v wind genny and was thinking about making two big 12v banks with individual dumps loads and program an arduino to charge the battery bank that is lowest via relays. Probably will never happen, just a thought. My end goal is to take all the 120v loads off the grid, with ability to switch back to the grid/generator. Please feel free to post any input you have on my system, I would love to here what you guys think.

This is my current parts list I have:
• 8 sharp 235w panels, 30v maximum power voltage, 3 on the roof, 5 waiting for more free time to mount.
• 8 breaker QO panel, paralleling all panels with individual 15amp breakers
• morningstar 60A MPPT, mounted not hooked up yet
• victron energy multi plus 3000w 24v inverter charger, not hooked up yet
• 12 used but still good 100ah agm batteries, 2 almost new 180ah telecom agm
• two sun600 GTI for testing panel angles, locations, will be sold as soon as I hook up the rest.

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Re: batteries, series-parallel, balancing, help me understand

Welcome to the forum.

Your basic question here is why do certain battery configurations cause trouble.

The biggest problem is in parallel connections: they provide multiple current paths which are almost never at the same resistance. As such one path will get more current, another less. When you apply that to charging or discharging batteries the result is some batteries get more charge and some less, some batteries do more work and some less. Pretty soon you end up with batteries at different states of charge; an unbalanced bank.

Any more than four parallel strings, even with bus bars or other common point connections, is begging trouble.
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Re: batteries, series-parallel, balancing, help me understand

By the way; do you want an analysis of the potential of your accumulated parts?

Normally you'd figure out how much power you need to supply first, then go get what will supply it. You've sort of started out backwards as so many people do. As Icarus says, "Avoid ready, fire, aim!"
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Re: batteries, series-parallel, balancing, help me understand

Just a thought but 8 x 235 = 1880w / 12v is 156.66 amps and @ 24v 78.33 amps. So would you not be pushing the CC past it's limits and losing a bunch of power?
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Re: batteries, series-parallel, balancing, help me understand
willardj wrote: »
Just a thought but 8 x 235 = 1880w / 12v is 156.66 amps and @ 24v 78.33 amps. So would you not be pushing the CC past it's limits and losing a bunch of power?

On 12 Volts, yes. On 24 Volts, maybe not: 1880 Watts @ 77% typical efficiency / 24 Volts = 60 Amps.
But it's a very near thing.
Re: batteries, series-parallel, balancing, help me understand

Here are some details about issues with series connections (from this post):
Add from Stephendv (Oct 20, 2011; -Bill:
stephendv wrote: »
... Victron has authored a great paper that covers some interesting material on charging forklift batts: http://www.victronenergy.com/upload/documents/Book-EN-EnergyUnlimited.pdf

From Mike90045,

A nice 54 page book on batteries--even includes a Battery 101 primer (series/parallel connections, etc.): (see attachment)
mike90045 wrote: »
Only if your battery stays below 70% charged for more than 24 hours. The lead sulphate crystals will harden, and not dissolve during discharge. This is called sulphation.

Say you loose 1% capacity each episode, and one episode a week. In a year, you have 50% degradation of your battery. That's what insufficient charging gets you.

See attached battery file for in depth explanation.

Sulfation - Formation of lead sulfate crystals on the plates of a lead-acid
battery.

Added 3/5/2012: Here is a nice thread on why I/we suggest not paralleling batteries if it can be avoided:

Series rule of thumb

Yes, I have seen a few top of lead acid battery balancers (typically 12 volt from what I recall--keep voltage "equal" across 24/48 volt battery bank sets by bleeding current around "higher voltage" cells/batteries. I looked for the product later--and could not find it--So I do not know if still available. RV industry has "balancers" DC to DC chargers which allow a pair of 12 volt batteries connected in series for 24 volt (motor start) to also power 12 volt appliances (house wiring).

I have also seen ads for commercial installations which are central battery chargers with a pair of leads for each battery/cell and they are all individually monitored (and some charging capabilities--if I recall correctly).

In the end, batteries have individual reasons for "their personal" voltage (mfg. variations, aging, sulfation, temperature, current flow/direction, etc.)...

And in a typical battery setup, there is very little "ballast resistance" (i.e., the wiring resistance is << battery resistance/impedance). So "current steering" is driven primary by specific battery conditions. Some conditions provide negative feed back (higher state of charge, battery voltage wants to rise). And others are positive feed back (charging batteries with lots of charging current/nearly full get hot--Hot batteries have depressed charging voltage--So draw more current, get hotter, etc... At the same time, a "dumb" charge controller not measuring battery temperature may think the battery bank needs more charging because of depressed voltage. Leading to possible thermal run-a-way).

From my own experience with designing "mid sized" distributed power systems/cabling, I found that the "low resistance" in a multi-path parallel setup (i.e., best connection) was the first cable/connection to fail (over current, I2R heating, cooked connection goes high resistance or melts). Then the next lowest path will overheat and fail, etc... Until the final connection(s) cannot handle the needed current flow.

So, my personal "rule of thumb" for designing a current sharing parallel cable system (without any specifically designed ballast/resistance to steer current) was a 1/N setup...

The first connection would be rated at 1/1 (i.e., 100% of rated capacity). The second would add 1/2 capacity (i.e., 50% more current). The third 1/3, etc... And, I used 3 parallel paths as the maximum parallel as being adding the most "useful" to the total current capacity (i.e., 1/4 would only add 25% more, etc.)...

At least in my time at the various companies, I had not seen any failures. (compared to equipment that had 5-10 parallel "heavy current" paths which "unzipped" connection by connection over the years).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Posts: 7Registered Users
Re: batteries, series-parallel, balancing, help me understand

Sorry about the delay responding, I never received an email notification. For the longest time I thought no one replied, lol.
Welcome to the forum.

Your basic question here is why do certain battery configurations cause trouble.

The biggest problem is in parallel connections: they provide multiple current paths which are almost never at the same resistance. As such one path will get more current, another less. When you apply that to charging or discharging batteries the result is some batteries get more charge and some less, some batteries do more work and some less. Pretty soon you end up with batteries at different states of charge; an unbalanced bank.

Any more than four parallel strings, even with bus bars or other common point connections, is begging trouble.

Thank you for that link, I am starting to see the light. I see how a very small amount of resistance can cause very uneven amp draw under load.
By the way; do you want an analysis of the potential of your accumulated parts?

Normally you'd figure out how much power you need to supply first, then go get what will supply it. You've sort of started out backwards as so many people do. As Icarus says, "Avoid ready, fire, aim!"
Ha ha, I've definitely been called icarus before, all jokes aside, I know how much I need, its more than all of this can provide, just picking up stuff as I find good deals and can afford them. The panels I got locally for a very good deal, the small agms I got for free, the telecom agms cam with the inverter and they all cost me less than the price of one of the telecom batteries new. The morningstar was what I could afford at the time. I will play with all of this and upgrade as I go, battery bank will have to be a more thought out decision.
willardj wrote: »
Just a thought but 8 x 235 = 1880w / 12v is 156.66 amps and @ 24v 78.33 amps. So would you not be pushing the CC past it's limits and losing a bunch of power?
From what I read the CC auto limits to 60 amps, the panels will not all be facing the same direction exactly so I don't think this limit will be reached often.
BB. wrote: »
So, my personal "rule of thumb" for designing a current sharing parallel cable system (without any specifically designed ballast/resistance to steer current) was a 1/N setup...

The first connection would be rated at 1/1 (i.e., 100% of rated capacity). The second would add 1/2 capacity (i.e., 50% more current). The third 1/3, etc... And, I used 3 parallel paths as the maximum parallel as being adding the most "useful" to the total current capacity (i.e., 1/4 would only add 25% more, etc.)...

At least in my time at the various companies, I had not seen any failures. (compared to equipment that had 5-10 parallel "heavy current" paths which "unzipped" connection by connection over the years).

-Bill

Thanks for the very informative post, even though I'm not sure I follow it 100% your N/1 setup sounds interesting. Do you have any pictures or diagrams of it? I'm a visual kinda guy.
Thanks everyone for responding, I will be moving forward with hooking alot of it up in the next few weeks so I'm sure I'll be back asking questions.
Re: batteries, series-parallel, balancing, help me understand

It is 1/N, not N/1...

Basically, if you have 5 parallel current paths, many people would use 5 * rated current (say 10 amps), and would design to support 5*10amps=50amps total.

My 1/N rule would be 10/1 amps + 10/2 amps + 10/3 amps + 10/4 amps + 10/5 amps = ~21.8 amps total supported current.

My experience has been that paralleling is that when powered by a voltage source (aka lead acid battery or electronic power supply), low resistance (need for low voltage drop with electronic circuits) cables+connectors do not share current very well unless you do something special.

With DC, that typically would be to add a "calibrated" resistance to each parallel circuit path that exceeds the variable resistance of the cable+connectors+terminations. But--that is not usually done because you were paralleling the cables to achieve a low resistance path in the first place.

So, that is where we are at with the typical parallel battery bank connections... The variability of the batteries (resistance, temperature, "operating voltage" points, chemistry variations, etc.) typically about match or can even exceed the resistance of the parallel cable paths themselves. This means that the actual current flow in each cable is highly variable and some sort of derating should be done to account for this.

The other option would be to add an extra length of cable (extra long, smaller awg, maybe a different alloy/material with higher resistance) to act as "ballast" and "force" better current sharing. This would work, and probably would work pretty well on a 48 volt battery bank--But not too well with a 12 volt battery bank as you have only a 1/2 volt or so of "voltage drop" headroom in the typical system for total wiring voltage drop.

Say you are looking at a "big" 400 amp 12 volt battery bank and load with 0.5 volt maximum wiring drop:
• V=IR; R=V/I
• R = 12 volts / 400 amps = 0.03 ohms

That is roughly on the order the typical resistance of a golf cart sized battery + cabling. There is just not the available voltage drop headroom to support adding significant ballast resistance for 12 volt system.

Anyway--long hand waving post cut short. A single current path driven by a "voltage source" has no sharing issues and is the 1/1 rating.

A two parallel string battery bank would be 1/1 + 1/2 or 1.5x supported maximum current of wiring. And three would add another 1/3 or 1.83x more current... Using my personal rule of thumb (it is probably very conservative--but it does work).

There are other issues with parallel battery banks (more cells to check for electrolyte levels, more chance for for "hidden" failures like open/shorted cells and open wiring, variable battery temperatures causing positive feedback for unstable current sharing, etc.).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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Re: batteries, series-parallel, balancing, help me understand
BB. wrote: »
It is 1/N, not N/1...
sorry it was late
BB. wrote: »
Basically, if you have 5 parallel current paths, many people would use 5 * rated current (say 10 amps), and would design to support 5*10amps=50amps total.

My 1/N rule would be 10/1 amps + 10/2 amps + 10/3 amps + 10/4 amps + 10/5 amps = ~21.8 amps total supported current.

My experience has been that paralleling is that when powered by a voltage source (aka lead acid battery or electronic power supply), low resistance (need for low voltage drop with electronic circuits) cables+connectors do not share current very well unless you do something special.

With DC, that typically would be to add a "calibrated" resistance to each parallel circuit path that exceeds the variable resistance of the cable+connectors+terminations. But--that is not usually done because you were paralleling the cables to achieve a low resistance path in the first place.

So, that is where we are at with the typical parallel battery bank connections... The variability of the batteries (resistance, temperature, "operating voltage" points, chemistry variations, etc.) typically about match or can even exceed the resistance of the parallel cable paths themselves. This means that the actual current flow in each cable is highly variable and some sort of derating should be done to account for this.

The other option would be to add an extra length of cable (extra long, smaller awg, maybe a different alloy/material with higher resistance) to act as "ballast" and "force" better current sharing. This would work, and probably would work pretty well on a 48 volt battery bank--But not too well with a 12 volt battery bank as you have only a 1/2 volt or so of "voltage drop" headroom in the typical system for total wiring voltage drop.

Say you are looking at a "big" 400 amp 12 volt battery bank and load with 0.5 volt maximum wiring drop:
• V=IR; R=V/I
• R = 12 volts / 400 amps = 0.03 ohms

That is roughly on the order the typical resistance of a golf cart sized battery + cabling. There is just not the available voltage drop headroom to support adding significant ballast resistance for 12 volt system.

Anyway--long hand waving post cut short. A single current path driven by a "voltage source" has no sharing issues and is the 1/1 rating.

A two parallel string battery bank would be 1/1 + 1/2 or 1.5x supported maximum current of wiring. And three would add another 1/3 or 1.83x more current... Using my personal rule of thumb (it is probably very conservative--but it does work).

There are other issues with parallel battery banks (more cells to check for electrolyte levels, more chance for for "hidden" failures like open/shorted cells and open wiring, variable battery temperatures causing positive feedback for unstable current sharing, etc.).

-Bill
I see, this whole "paralleling all these batteries thing" isn't going to work like I thought it would. Just curious, I know you are not supposed to parallel batteries of different AH capacity, but what would happen if I paralleled the 100AH's and the 180's together? I am looking into getting a forklift battery, seems they have a long lifespan and lots of amp hours, if you can move one.
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Re: batteries, series-parallel, balancing, help me understand

Depending on how much difference there is in capacity paralleling dissimilar size batteries will either shorten the life of one or the other by a little bit or by a lot. Your 180 & 100 Amp hour example is pretty far apart: 10% current on a 100 Amp hour battery is 10 Amps; 10 Amps on a 180 Amp hour battery is 5.5% So if you use that peak charge current the 180's will get barely charged, sulphate early, and die too soon. Reverse the situation and put 18 Amps to the 100's and they will get hotter than normal and suffer from plate stress and early death. The greater the difference, the greater the effect. If you try to pick a current "in the middle" each will suffer in its own way and lose years off the expected lifespan. That is if you could keep the charge current consistent. Since it varies, so will the effect. Nor will the absorb time or discharge rate be equal. Always one of the batteries will have "too much" of whatever and the other "too little". It is the worst of all possible worlds as far as the batteries are concerned because neither will ever be in a state where it gets the right conditions.

Forklift batteries are fine if you have a forklift to move them with.
Kind of expensive, though.
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Re: batteries, series-parallel, balancing, help me understand

well I got the inverter mounted, and both CC and inverter wiring, fuses and disconnects hooked and started charging, finally;), but as I have read many times, you never get any sun when you want it, it was pouring rain. The victron inverter works very nicely, I am very happy with it. I am temporarily using the 100ah AGM's for now, a new battery bank will come when the budget allows, as this is a sorta hobby/back-up power thing anyway, not an off grid set it and forget it system, I will be closely monitoring the batteries and shutting down the system when I am not home. I set aside two batts for a ride on toy project I building for the kids, so I am using the remaining 10 on the solar system. I used copper bus bar to make 5 24v strings using "method two" here http://www.smartgauge.co.uk/batt_con.html. Now some of these batts are definitely of different SOC and age, when I let the inverter crank 70 amps into the bank, a couple of the batteries shot up over 15v and started venting. I pulled these batteries down with a 12v load tester as they were absorbing and got the voltages pretty even, but I know this is not a long term solution. since a new battery bank is not in the budget yet, and I have other string applications I would like to use these batteries for in the future, I would like to build charging shunts to shunt an amp or two when a battery goes over about 14.2v, like the lithium batteries do. Any one know of a cheap and easy circuit I could build?
Re: batteries, series-parallel, balancing, help me understand
js35 wrote: »
I used copper bus bar to make 5 24v strings using "method two" here http://www.smartgauge.co.uk/batt_con.html. Now some of these batts are definitely of different SOC and age, when I let the inverter crank 70 amps into the bank, a couple of the batteries shot up over 15v and started venting. I pulled these batteries down with a 12v load tester as they were absorbing and got the voltages pretty even, but I know this is not a long term solution.

The problem here is that you have two batteries in series that are not evenly "matched". The reasons include:
• Different AH capacity batteries (180 and 100 AH). The 100 AH battery will become fully charged first (and eventually vent) while the larger battery still is charging
• The two batteries in series are of differing ages/capacities (due to age/wear and tear). Again, the smaller battery will reach 100% charge first, and eventually start equalizing and/or venting (if AGM/Sealed type).
• The two batteries are "identical" (usually within 20% of each others capacity, same chemisty--I.e., pair of AGMs, pair of XYZ flooded cell, etc.), but one battery was significantly less charged than the other (one near 100% one at 50% or similar). Here, you would fully charge each battery first, then put them in series and they should then "track" state of charge together.

There are ways of "balancing" batteries. I have, in years past, seen smaller cell/battery by-pass charge controllers for lead acid--but nothing lately.

And you can buy and wire up DC to DC charge controllers which will balance significant loads across batteries:

Look at the last example in this Application Note about Battery equalizers:

www.solarconverters.com DC to DC Converter Application Notes

This product is really interesting--It is bi-directional--so it can balance loads and charging currents. However, it is not cheap enough to justify buying one for each parallel battery string unless you tie the mid-12 volt point together in series too (I usually recommend against doing this--makes current path through the batteries much more complex and makes it more difficult to find wiring/battery/cell problems). But it would work.

Also gives you the ability to draw 12 volts from a "24 volt" battery bank without damaging (recommend to stay near or below the maximum current rating of the "balancer" DC to DC Converter.

-Bill

I will add my standard note on paralleling/complex battery wiring setups--Get yourself an inexpensive (or expensive) DC Current Clamp Meter. This one from Sears is "good enough" and also has standard DMM and AC current clamp capabilities. This allows you to measure the current in each battery and quickly find batteries and connections that are not properly sharing the loads/charging currents.
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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Re: batteries, series-parallel, balancing, help me understand

I am not using the 180's, I gave those as well as one of my old 12v inverters to my father to use as back up power. I have seen those devices but they are all more money than what I want to spend at the time, might as well buy new batteries for that kind of money. All I am looking for is a simple electronic circuit I can buy the components inexpensively, solder them together and mount one on each battery to help avoid venting.
Re: batteries, series-parallel, balancing, help me understand

The problem is that you could build (or buy) a smaller "linear" device to balance current. Linear devices waste lots of energy as heat (for example bypassing 2 amps at 12 volts around a battery would dissipate 24 watts--large heat sink required and lots of wasted energy). Set up a pair of comparators (or voltage controlled switches)--that monitor the voltage across each 12 volt "battery block"... Which ever one is "higher", turn on the dump load. If the batteries are within 0.2 volts of each other, then leave the dump loads off).

A DC to DC converter will only waste about +/-5% of the power as heat (24 watts * 0.05 = 1.2 watts or a bit more)--But cost you money. A "typical" DC to DC switching power supply is gong to cost around \$1 per watt in volume production (really high voltage/cost reduced power supplies can be near \$0.50 per watt)... And specialized units, in small volume, could cost upwards of 2x that amount.

There are also PWM solar charge controllers that have "dump" load control mode. Just set them to 14.2 volts--put one on each 12 volt battery block and attach your load(s) to the controller (Xantrex Cxx series, and MorningStar I think, has some controller with that mode, etc.)... But you are still looking at something like ~\$100 per PWM/Dump controller.

In the end--Either you have an initial charge imbalance--which just needs each battery charge individually to 100% SOC... Or you have unmatched batteries (probably because one of them is near failure--sulfation, shorted cell, etc.) and it not long for this world anyway.

I know nothing about this product--But it is listed as a charge controller per battery type application (\$75 each).

If you are going to try and keep this bank working--I would tie the 12 volt intermediate posts together in parallel and build a dual 12 volt isolated comparator+dump loads+dump controller, get a pair of something like the \$75 unit above, or the DC to DC 12/24 volt converter in the previous post. And get a DC Current Clamp meter (if you don't have one).

If nothing else, it will keep you off the streets at night monitoring your battery bank/charging systems. :-)

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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Re: batteries, series-parallel, balancing, help me understand

funny, but they are all now balanced enough where I can leave them on without fear of cooking one. There are two strings that do each have one battery that seems to sit higher than the other on the string when charging, and while I got others to even out they seem to be stubborn, they are both the newest looking batteries too, so I may re-arrange the good ones together on the same string. Other than that they all seem to stay within .05 volts of each other. Individual PMW controllers would be way overkill for what I want to do. A little bit of wasted heat in the absorption stage isn't going to hurt anything, I think I'm going to just use a couple a couple zener's with a automotive fog lightlight bulb or something like that to bleed off a little current whenever one starts to get a little higher than 14.2v. This is just until I find a good set of some sort of traction battery. I have several amp clamps ranging from 4-400 amp range. Interesting read here on mixing battery banks of different capacity: http://neuralfibre.com/paul/wp-content/uploads/2007/05/can-we-now-sin.pdf
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Re: batteries, series-parallel, balancing, help me understand
Forklift batteries are fine if you have a forklift to move them with.
Kind of expensive, though.

Big and heavy, but cost per AmpHour was comparable, for me, to Trojan's cheapest L-16 for the capacity. L-16's were @\$250 x8 + exchange of \$12 per + interconnects for 740 Amp hour capacity, I pick up 100miles, 805 Amp Hour(20 hour) forklift was \$2327 + \$175 for a lift gate truck = 2512 delivered moving 10-12 feet took a day of thinking and a few hours with a heavy 4x4's,and a big lever with a big funny looking guy on one end...

I'll let you know in 10-12 years if it was a good investment.
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
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Re: batteries, series-parallel, balancing, help me understand
Photowhit wrote: »
Big and heavy, but cost per AmpHour was comparable, for me, to Trojan's cheapest L-16 for the capacity. L-16's were @\$250 x8 + exchange of \$12 per + interconnects for 740 Amp hour capacity, I pick up 100miles, 805 Amp Hour(20 hour) forklift was \$2327 + \$175 for a lift gate truck = 2512 delivered moving 10-12 feet took a day of thinking and a few hours with a heavy 4x4's,and a big lever with a big funny looking guy on one end...

I'll let you know in 10-12 years if it was a good investment.
how are they performing for you? I am hoping to get a good used pack locally, there are tons of industrial warehouses around here that use them.
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Re: batteries, series-parallel, balancing, help me understand

I'm happy so far, I actually bought a new place shortly after the battery purchase, another point of buying a large battery, I would have gone 48v if I knew I was going to buy the new place and put in solar. So I have used the battery mostly on weekends 24V, everything has checked out well, actually used less water than I had anticipated (I was warned they really go through the water, but hasn't been much at all, likely if I had battery miser's on them I might have only watered once.

I've ran an A/C off the system over night 2 nights every weekend but one this summer, have my system setup to do monthly equalizing, the system is minimal for this size battery, @1700watt array, I have the panels to take it to 2000 watts, but didn't bother since i was only using on the weekends. I know it has reached float even with my over night A/C the couple times I was there with out having to work the following day.

I'll move it to the new place (more issues with a large battery) I have a couple farmers around who will help me out, but I'll likely give them \$100 if it takes a couple hours more if longer, and have too large an array and somewhat load. I'll likely use 11 KWH's a day over the summer, though our heat normally comes with sun and with too large an array, I'll run the A/C regularly during the day over the summers. I'll use less than 2KWH's a day during the winter.

I'd do grid connect, but we have a goofy coop electric who really doesn't want net metering, Electric here costs \$25 'line fee' before you buy electric, so at 2KWH a day 30x.09 = \$2.70 + \$25 = 27.70/60 = almost 50 cents a KWh and they had planned on an increase in the line fee before the economy took a dump, so that's coming...
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
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Re: batteries, series-parallel, balancing, help me understand

How is that forklift battery configured? Is is one series string? and if not, how many parallel strings?
• Posts: 4,668Solar Expert ✭✭✭✭
Re: batteries, series-parallel, balancing, help me understand

Small by forklift standards, one 'string' looks like one battery, but is 12 cells(or jars) in a steel case with solid interconnects, I had them build mine with flags since they were having problems understanding and quoting me a price for 3' appliance side wiring to match their connectors. It's a 12(Cells)-85(Ah for 2 plates, 8hr)-13 (number of plates)
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.