Inverter/Deep Cycle battery charging question

I had to replace one of my inverters due to a lightning surge (had surge protection but it failed...) - the one I had had a single rated 20amp charger built in and this seemed to work well with my setup of 2x 100ah deep cycle batteries (24v system - 2x 12v batteries in series). That was until the lightning fried the charger and it overcharged the batteries...

The new inverter however has a a selector switch for the built in charger, with 5/10/15/20/30 amps listed. The default setting is 5 amps.

What would be the best setting for the charger - 20amps?

From what I understand, the maximum constant current rate in amps should be approximately 20% of the amp hour rating of the battery, so for a single 100ah battery this would be 20 amps, however if there are 2x 100ah batteries in series, would 20 amps still be fine to charge both simultaneously?

If I were to add another 2 batteries in series, then parallel them to the existing setup, would I need to crank up the charger amps to 30 amps max, or would 20 amps still do the job (just taking longer to fully charge)?

I've also read that deep cycle batteries should be charged on a lower the amp setting to get more life from it (if you have the time), however others say use a higher amp rate then float charge...

It all depends on the amount of time you have to charge the batteries, and the load you have on the inverter.

The faster you want to charge the batteries the higher the amperage you need to set it to. I have seen people charge a 100ah battery with a 1ah charger. It just takes a really long time.
It also depends on how flat the batteries are, but your invertor should not draw the batteries below about 30% as a standard so even the 5ah setting would charge the two batteries just fine over 12 hours or so.

If you add another bank of two chargers I would set that up to 10ah but if you double the batteries and not the load then 5ah should still be sufficient for the same period.

Lower amperage is definitely better for a cycling battery, however if you have a really flat battery you will need a higher amperage to get it going. You should never be dealing with totally flat batteries on an inverter tho.

Put it on 5ah and see if you have diminishing capacity then up it to 10ah and so on. If this is primarily for load shedding then for stage 1 and 2 I would leave it on 5 ah and put it on 10ah for stage 3.

All of this depends of course on the KVa of the inverter and the total load you have running off it. Just remember that adding battery does not mean you can add load. If you compare an inverter to a car, the inverter is the engine and the batteries are the fuel tank.
By adding fuel tank does not mean the car can pull a heavier load. It means it can go further with the same load.

Also remember that the higher the amps the more electricity you use.

What are the specs on the batteries.
That should give you the best settings as each type of battery is different.

Many thanks Madman88.

The inverter is 2000w 24v and the load will range from 350w-800w max during loadshedding. I don't foresee the batteries draining below 50-60%, however it would depend on the power drawn during loadshedding.
I'll set it to 5amps and see how it goes - in the worst case scenario where we have 2x 4 hour cuts per day, I'd need the setup charged within 6-8 hours. Will crank it up to 10amps if the charging is slow.

I want to add the 2 extra batteries to give a longer run time if needed - the load will probably never go beyond 1000w

Fuzzbox said:

What are the specs on the batteries.
That should give you the best settings as each type of battery is different.

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Thanks Fuzzbox.
I'm picking up the new set of batteries on Monday (old ones boiled and are knackered...). Will check the specs when they arrive.
The specs I found online indicate a recommended charging ampere of 0.1C.
Therefore 0.1 x 100A/h = 10amps charging if my calculations are right.

What fuzzbox said. All you need to do is check the spec sheet and see what the maximum charge current is and make sure you don't go over that.

But also don't charge it too slow which is also not good for the battery. 10A is minimum imo

The_Traveller said:

What fuzzbox said. All you need to do is check the spec sheet and see what the maximum charge current is and make sure you don't go over that.

But also don't charge it too slow which is also not good for the battery. 10A is minimum imo

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Thanks The_Traveller, noted.

So by having more than one 100ah battery in series or parallel makes no great difference in the charger requirement, it would just take longer the more batteries added. If I add the extra set of 2x 100ah's for additional run time, I should still be able to leave the charger selection switch on the inverter set at 10amps - or should this be increased to 15 or 20?

My other 24v inverter setup already has 4 batteries (2x 12v in series and paralleled to 2x 24v) - the charger on this one is not selectable and has a static charge rate of 30amps - is there a "maximum" number of batteries that can then be connected to this 30amp charger output?

Sorry for all the questions, but the more I search online, the more the answers differ and seem inconclusive... just looking to optimally configure the setups in order to prolong the batteries and inverter/charger life.

howardb said:

Thanks The_Traveller, noted.

So by having more than one 100ah battery in series or parallel makes no great difference in the charger requirement, it would just take longer the more batteries added. If I add the extra set of 2x 100ah's for additional run time, I should still be able to leave the charger selection switch on the inverter set at 10amps - or should this be increased to 15 or 20?

My other 24v inverter setup already has 4 batteries (2x 12v in series and paralleled to 2x 24v) - the charger on this one is not selectable and has a static charge rate of 30amps - is there a "maximum" number of batteries that can then be connected to this 30amp charger output?

Sorry for all the questions, but the more I search online, the more the answers differ and seem inconclusive... just looking to optimally configure the setups in order to prolong the batteries and inverter/charger life.

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Ideally it is not really suitable to connect more than 2 strings of batteries. It is not harm trying 3 and see if you get any voltage drop. If you are adding more batteries in parallel then surely increase the charge current, but again, don't go over the batteries limit.

I tested it myself but with 4 in series so total 12 . I had some problems and had to remove 4. But it could have been a few other factors causing this problem. Had no time investigating because it is not my personal system.

I am buying another system for my cousin. its a 3kw 24vdc with a 30A charger built in. Supplier gave me go ahead to connect 6 x 12v200ah . He said that the batteries must get enough charge with this kind of a setup so if loadshed happens every day for only a few hours then we safe. but if it goes on for 12 hours + and the very next day again power cut, then obviously the batteries didn't get its full charge and that's not good for batteries.

Spec sheet? Ive sold tons of these batteries, been in the industry for 15 years and I have never seen anywhere that it states the minimum charge rate for a 102ah battery. If the battery is used in an automotive application and has been drained due to a faulty alternator or some other drainage on the vehicle then the absolute minimum is 10ah but then imo 10ah is not nearly enough to put current into the battery again. We start the charge on something like that much, much higher for the first little bit. You are not (and never should be) dealing with drained batteries.

I have the specifications of the batteries and 99% of them apply to the automotive industry. For the backup industry where the battery is not working as hard since the current drawn is constant and there is no cold cranking needed 5ah should be sufficient given enough time.
The actual charge required to charge a battery is determined by the remaining capacity in the battery. The flatter the battery, the more current it needs to charge (at a constant speed). When we charge flat batteries we estimate that the first 80% of the charge process only charges 40% of the battery. The final 20% of the process puts 60% of the charge into the battery since the more the battery is charged the easier it charges. So if you where to say "minimum 10ah" I would have to ask : At what point?

For example:

System a.
You have 800w load on two batteries and they run down to 40% capacity over 4 hours of use and

system b.
you have 800w load on four batteries and they run down to 70% capacity over 4 hours of use (it would actually be a little less than that, probably around 75% but for the sake of keeping it simple say 70%).

Because you have a higher capacity remaining in system b in the 4 batteries it would actually charge with less ah than system a since the lower the available capacity the higher the current required to charge. Also, the more available capacity the faster it charges, so system b would charge faster then system a.

There is no "minimum". To be honest tho, when it comes to lifespan and electricity usage there is no great difference between 5ah and 10ah, and since the chargers in these inverters will shut off when the battery is charged you should not be able to damage the battery by putting it on the higher ah.

Like I said before, you can put as many battery banks as you want on a system. The battery is the fuel tank of the system. As long as you don't add load or increase the voltage you wont have a problem. 204a/h should be giving you about 8 hours of uptime at about 400w.

/\ the reason why people have so many problems with battery backup systems ...

Yea cos spreading misinformation totally helps people

Thanks for the info guys.
I'll set it to charge at 10amps on the 2-battery setup and will see how it goes after the next power cut. Batteries only coming Monday now, so can't do much more this weekend.

howardb said:

Thanks for the info guys.
I'll set it to charge at 10amps on the 2-battery setup and will see how it goes after the next power cut. Batteries only coming Monday now, so can't do much more this weekend.

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What did you buy ....?

Royal Delkor DC31 deep cycle marines
They were the only ones I could get within a few days, everyone else is pretty much sold out with stock only arriving end March.
Will grab some additional OmniPower or Deltec ones late March for my main inverter setup.

howardb said:

Royal Delkor DC31 deep cycle marines
They were the only ones I could get within a few days, everyone else is pretty much sold out with stock only arriving end March.
Will grab some additional OmniPower or Deltec ones late March for my main inverter setup.

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I suppose it depends on which Deltecs but I'm really not impressed by their pricing versus the actual "performance" (albeit claimed).

Zenbaas said:

I suppose it depends on which Deltecs but I'm really not impressed by their pricing versus the actual "performance" (albeit claimed).

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True, pricing has increased since I last bought. My previous 1251's (I think) lasted a good while - got them in 2010, so not too bad; performance also seemed good. Based on current pricing I'm in two minds though - got slightly better performance from the Royals which were way less to purchase.

howardb said:

True, pricing has increased since I last bought. My previous 1251's (I think) lasted a good while - got them in 2010, so not too bad; performance also seemed good. Based on current pricing I'm in two minds though - got slightly better performance from the Royals which were way less to purchase.

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What did the Royals set you back and from where...?

Zenbaas said:

What did the Royals set you back and from where...?

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R1595 each incl scrap battery swop (R185 extra if no scrap battery).
NRG Tech in Centurion.

I am new here. Hello Guys

The whole battery charging thing with SLA and depth of discharge and stuff can really be confusing. I played with Cyclons years back in 2005 when ESKOM first started their crap. Experimented with the 8Ah setup of 2X 6V packs in series. Amazing very expensive batteries that the Military and Medical use. They require no current limiting when charging provided they are told to stop charging with a charger that cuts off power @ 13.8V terminal Voltage (basic).

You can literally throw the kitchen sink at these things....set your terminal voltage and they will take all the Amps they need to get there.

I stuffed these batteries up as small as their Ah capacity is....I built my own charger for them. A normal Linear charger with a Toroidal transformer and lot's of heatsinking and delivering around 4 to 5ADC to charge the little 8Ah set up. Was not good enough and could not handle cycling with a *** charger.

Roll on to late 2014 when ESKOM started their crap again. I started re learning and seriously investigating stuff on the Net.

So much more out there now. Check out this link about battery charging: http://www.otherpower.com/off-grid-battery-guide
(Their whole site is very interesting to read).

Like it says, undercharging is a slow killer of SLA batteries.

Anyway, to not make the same mistake again, I bought and did not build.

I stay in a room in deep territory and have no use for anything except Internet, Modem, Cell charger, TV (SABC ),my little LED light, front of shop Card Machine, Till and Security gate.

Total Watts maybe 200 to 250 on a 360W rated Stepped Sine Wave inverter dating back to around 2001 (PowerMan).

Purchased the Battery just before Xmas last year: http://www.mantech.co.za/ProductInfo.aspx?Item=370M0014
I let it just sit there through Xmas while I was deciding how the hell I am going to charge it if and when I use it...my charger consisting of all the bits and pieces and it's few Amps from the Cyclon experience in 2005....would end in tears and money wasted.

I just need to briefly add this: I know the Ritar is not a Cyclon...but you get the drift....plus the Ritar is approximately 8X bigger in capacity than the Cyclon.

So me being a SMPS hater and all (I fix cheap Chinese SMPS every day here)...decide that Linear to charge this 65Ah will not cut it. So I start investigating on the Net. Looking for a quality SMPS SLA Battery charger. Find this company: http://www.meanwell.com/

Impressed I see Mantech here stocks them. Yay

I bought this one: http://www.mantech.co.za/Stock.aspx?Query=372M0529and

The 65Ah Ritec Maximum suggested charging current is 19.5A. The MeanWell charger puts out 20.85A Maximum. The charger has no cooling fan and thermally throttles and hugs the battery and keeps it safe.

A few facts and figures:

2 Hour blackout with this little setup swings the battery around within 2 Hours of ESKOM coming back.

Charger hot but only while getting all up to speed again for the next bout.

My first and looong and boring post. Shoot me down or come and see for yourself.

Thanks for the info amongstthevotingfodder, interesting reading and links