Max amperage usage without damaging batteries

I wondered if anyone had some ideas about the max amperage usage on batteries without damaging them.

Currently I am running 4 x 120 ah AGM gel batteries to power the caravan. However in the evening this powers a 81cm LED TV and this with the DVD player is sucking 16amps. If I play the XBOX this will increase to 22 amps.

Not withstanding the wiring which can handle this, I wondered if batteries can be safely drained at this rate. I am careful about never letting them drop below 10.6 volts or 80% on the capacity on the xantrex battery cauge.
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Reply By: Maîneÿ . . .- Thursday, May 20, 2010 at 08:26

Thursday, May 20, 2010 at 08:26
carlsp,
10.6v is basically dead flat

Voltage State of Charge
12.7v 100%
12.5v 90%
12.4v 80%
10.5v 0%

I think the "xantrex battery cauge" is ***** if it states 10.6v is 80% charged.
(I am careful about never letting them drop below 10.6 volts or 80% on the capacity on the xantrex battery cauge)
AnswerID: 417336

Reply By: gbdid - Thursday, May 20, 2010 at 08:26

Thursday, May 20, 2010 at 08:26
Are you sure about 10.6V being 80%?
Most state of charge tables would have 11.6V being flat,12.7 being full and 80% being about 12.5V.
I think the general recommendation is not below 50%, which is 12.1V on the SoC tables I use.
AnswerID: 417337

Follow Up By: ChipPunk - Thursday, May 20, 2010 at 11:45

Thursday, May 20, 2010 at 11:45
That's the difference between open circuit (no load) and during discharge.

The 11.3-12.8V SOC is to test an unloaded rested battery.

Tables that talk about 10.5V, 10.8, 11.1V endpoints are referring to battery terminal voltages at the tabulated load (usually high discharge rates).


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Reply By: Ozhumvee - Thursday, May 20, 2010 at 08:28

Thursday, May 20, 2010 at 08:28
Ideally you should never go below 50% capacity which is approx 12.2 volts.
I would think that at 10 .6 volts you are doing serious harm to your batteries.
My experience is mainly on normal wet cells where you are seriously damaging the battery at that voltage. Others will have more knowledge on AGM's but I suspect that the 50% point is still ideal.
Peter
1996 Oka Motorhome

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Reply By: Member - Teege (NSW) - Thursday, May 20, 2010 at 08:38

Thursday, May 20, 2010 at 08:38
The things we have to worry about when we go camping!!! I guess you only use the dishwasher and the washing machine when you can access 240. But then again the 15 amps available in caravan parks probably wouldn't cope with that load either.

teege
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Follow Up By: carlsp - Thursday, May 20, 2010 at 08:53

Thursday, May 20, 2010 at 08:53
After 15 years in a army recon unit, I have had my fill of sitting on top of some desert hill eating cold goat like the natives.

Now I prefer a hot shower and sitting beside the campfire in a comfortable chair watching the outback sunset in Australia. At the same time watching foxtel's telecast of the football on my big screen tv mounted to the side of the caravan.

We used to have a saying "Any idiot can be uncomfortable". Camping for one person is different for others.
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Follow Up By: dbish - Thursday, May 20, 2010 at 10:52

Thursday, May 20, 2010 at 10:52
Well said Carlsp. Daryl
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Follow Up By: ob - Thursday, May 20, 2010 at 11:18

Thursday, May 20, 2010 at 11:18
Just a thought

Why not stay home where you can have all the hot showers and foxtel watching you like without worrying about things like batteries...........oh and get a nice big mural of a sunset painted on the wall behind the 1000" tv and you got it licked..............lol
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Follow Up By: TerraFirma - Thursday, May 20, 2010 at 11:25

Thursday, May 20, 2010 at 11:25
Very funny..! LOL yeah staying home means you don't have to worry about creating all the luxuries when your away camping.? Like Hot Water, TV, The Xbox, makes you wonder why you'd go camping at all..? LOL
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Follow Up By: Alloy c/t - Thursday, May 20, 2010 at 17:02

Thursday, May 20, 2010 at 17:02
Terra + Ob , makes you wonder , this is the same bloke who recently had the dummy spit over the fact that small outback communities are NOT just there to cater for tourists and have 24/7 sevices , truth be known all his info is from the TV.
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Follow Up By: Steve and Viv - Saturday, May 22, 2010 at 14:33

Saturday, May 22, 2010 at 14:33
As longs as I don't have to watch or HEAR your TV on the side of your van in MY camping spot aye !!! Had some one do that at Edith Falls - very annoying.

As far as your batteries go. Just use them and when they fail because they have been taken to low, get some more :-)
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Reply By: Member - Andrew (QLD) - Thursday, May 20, 2010 at 09:03

Thursday, May 20, 2010 at 09:03
Assumption in my answer: the 16A is total load across all 4 batteries, not just 1.

To answer the main part of your question, yes the batteries would be able to handle this nicely. If you check the manufacturers website, they will more than likely have the specs for the batteries including discharge characteristics.

For example, a fullriver DC120-12 rating is based on 20 hours at 6A (plus a couple of other conditions)....noting that 4 (batteries) x 6A =24A, being slightly more what you believe is being drawn from your system.

If you are to limit the discharge to less than 50% (a common recommendation) means that you should use them for no longer than around 10-12 hours before recharging fully.

All ballpark figures of course. Hope that helps.

Andrew
AnswerID: 417343

Follow Up By: carlsp - Thursday, May 20, 2010 at 09:23

Thursday, May 20, 2010 at 09:23
Thanks Andrew,

Got that. I have worked out that the fridge and cooling fans (computer fans x 3) are running 10amps all the time. During the day this is more than covered by the solar panels. So in the evening this 10 amps + another 15amps (for tv) will be OK for 4 hours. (sunet till 10pm).

Then the following morning I have them back to 100% by 1100 hrs.

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Follow Up By: Member - Andrew (QLD) - Thursday, May 20, 2010 at 09:45

Thursday, May 20, 2010 at 09:45
Sounds like a good system that can handle the anticipated load. Though a week of rain may change the situation. :)

Andrew
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Follow Up By: Gronk - Thursday, May 20, 2010 at 10:29

Thursday, May 20, 2010 at 10:29
A worthwhile addition to any camping setup is a cheap digital multimeter..

That way ( apart from any other uses it may get ) you can be pretty sure what the voltage is ( and also lets you see if the other gizmos are accurate )..

That way, you can watch all the telly you like ( or drink as much cold ale as you like ) until the batts get down to the magical 12V area before you need to recharge..

Don't forget, to get a reasonably accurate idea of "proper" voltage, you may need to experiment a bit and find out what the no load voltage is at any given point ??

With that sort of load, when you think its getting a bit low....turn off all your loads for 10-15mins and see what the voltage "bounces" back to ??

Doesn't take long to work out that for example at 11.5V under load may be in fact 12.1V no load ??.....so the 11.5V could be your reading that you decide is the lowest you want to go !!!
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Reply By: Spade Newsom - Thursday, May 20, 2010 at 10:17

Thursday, May 20, 2010 at 10:17
In carlsp's set up what might be too big a continuous amp draw before batteries won't function properly? I don't mean damage from drawing until flat and I assume large enough wires.

eg If he wanted to draw say 100, 150 or 200 amp for a continuous hour. How many amps can the inner workings of the battery literally keep up to the drain at the terminals? The amps required to start a car can only be sustained for a short period so that number is too high of course.

Hope the question is not too confusing (or too stupid).


AnswerID: 417348

Follow Up By: Member - Andrew (QLD) - Thursday, May 20, 2010 at 12:18

Thursday, May 20, 2010 at 12:18
It would depend somewhat on the particular battery and the manufacturers specifications. In the link i supplied above, the maximum discharge current for one battery at 25C is 1200A for 5 seconds!

My understanding is that the internal resistance will limit the demand at a higher load (A) as the voltdrop will be significant. For example at 900A for 30 sec at 0C the reading willl be 7.2V......in many cases a low enough number to be useless to run many applications.

The discharge curves of the battery mentioned seems to limit it to around 200-300A, though it will be only give 6-7 minutes. Real life values may vary due to age etc.

Happy to be corrected if wrong. :)

Andrew
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Reply By: TerraFirma - Thursday, May 20, 2010 at 11:22

Thursday, May 20, 2010 at 11:22
It's not a good idea to go below 50% on a regular basis. Will also depend on your battery type, heavy duty deep cycle or a hybrid type battery, the heavier duty batteries have thicker plates to deal with regular discharge rates. With 480AH what sort of charger are you using, I would have thought something with a 50A capacity would help keep things charged.?
AnswerID: 417363

Reply By: Member -Signman - Thursday, May 20, 2010 at 11:32

Thursday, May 20, 2010 at 11:32
State of Charge (%) OCV per cell OCV per 12V battery
100 2.17 or greater 13.0 or greater
75 2.10 12.6
50 2.03 12.2
25 1.97 11.8
0 1.90 or less 11.4 or less




AnswerID: 417367

Reply By: ChipPunk - Thursday, May 20, 2010 at 11:58

Thursday, May 20, 2010 at 11:58
As I just posted above, do not confuse open circuit (no load) and discharge voltages.

The 11.3-12.8V SOC is for an unloaded rested battery.

Tables with 10.5V, 10.8, 11.1V etc endpoints are referring to battery terminal voltages at the tabulated load (higher discharge rates having lower voltage endpoints).


The higher the current discharged from a battery, the lower its life.
Staying with the manufacturers recommended ranges should provide the stated life. Some 10-year batteries are 5-year batteries with lower discharge curves etc. Same as some deep-cylce batteries are "de-rated" cranking batteries.

But your load seems to be well within battery ratings.


Usually the most important consideration is recharging ASAP after a discharge and fully recharging the battery(s), not overcharging, and keeping the discharge amount as low as possible.
There are a plethora of solutions to make up for the above - eg - burning off sulphated plates etc, not that all will recover a damaged battery - ie, a collapsed cell.
AnswerID: 417369

Reply By: Crackles - Thursday, May 20, 2010 at 15:31

Thursday, May 20, 2010 at 15:31
"....max amperage usage on batteries without damaging them"
An electric winch pulls between 100 to 450 amps under load so I doubt 22 amps shared between 4 batteries will cause any issues.
I reckon you'll have more than enough capacity in reserve to run your XBox together with the electric balnket, coffee machine & popcorn maker. Enjoy :-)
Cheers Craig.........
AnswerID: 417390

Reply By: Member -Dodger - Thursday, May 20, 2010 at 16:39

Thursday, May 20, 2010 at 16:39
Enlighten me I have never heard of AGM Gel batteries. I always thought that Gel batteries and AGM batteries were two different types????????????
I used to have a handle on life, but it broke.

Cheers Dodg.

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Follow Up By: Member - Andrew (QLD) - Thursday, May 20, 2010 at 16:58

Thursday, May 20, 2010 at 16:58
Please don't be sarcastic....
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Follow Up By: Alloy c/t - Thursday, May 20, 2010 at 17:09

Thursday, May 20, 2010 at 17:09
Andrew , what sarcasm ? AGM= Absorbed Glass Mat , Gel = A jelly like substance instead of liquid between the plates , 2 Totally different battery types that require different charging voltages , sarcastic ?
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Follow Up By: ChipPunk - Thursday, May 20, 2010 at 21:08

Thursday, May 20, 2010 at 21:08
Correct.
Gel & AGM are both lead-acid batteries.
Both are "sealed", but only the AGM is an "SLA" (apparently).

And Gel & AGM are quite different in terms of behaviour and treatment.
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Reply By: Ianw - Thursday, May 20, 2010 at 20:08

Thursday, May 20, 2010 at 20:08
Vision brand batteries (one of the best from China) states that 12.4v equates to 50 % SOC. Under load you can discharge until the volts = about 11.8v and it will then recover to the 12.4v when rested. To recharge to 100% will require at least 24 hours on a charger. Most of us cannot provide this time on charge. So because we are starting at say 80% to 90% max, we really only have access to 40% of our batteries' rated capacity, and only then if it is new. At 35 deg C your battery's life is reduced to half that stated in the specs !!

Ian
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Follow Up By: ChipPunk - Thursday, May 20, 2010 at 21:15

Thursday, May 20, 2010 at 21:15
Crikey - my discharges to 10.5V would recover to ~12.4 if 50% discharged!
What discharge rate are they quoting?

(The point of this reply is that there is point quoting an end-voltage of the discharge current/rate is not disclosed. 50% is 50%. The end voltage depends on the discharge current or power...)
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Follow Up By: Ianw - Thursday, May 20, 2010 at 21:20

Thursday, May 20, 2010 at 21:20
C10

Ian
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Follow Up By: ChipPunk - Friday, May 21, 2010 at 10:29

Friday, May 21, 2010 at 10:29
Oops - my bad.

I meant Amperage rate.... LOL
(UPS batteries - typically list current and minutes to a voltage endpoint 1.7, 1.75, 1.80 etc Volts/cell).
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Follow Up By: Ianw - Friday, May 21, 2010 at 22:39

Friday, May 21, 2010 at 22:39
As I said, C10 rate. C10 is the amps used to flatten the battery in 10 hours. i.e a 120 Ahr battery rated at the C10 rate will supply (when new) 12 amps for 10 hours and will then be at the rated voltage of 1.8v per cell (or 10.8v for a 12v battery.) i.e, dead flat !! But as most AGM batteries are rated at the C20 rate (i.e. for a 120 Ahr battery, C20 is 6 amps), if you discharge at the C10 rate you will only get maybe 110 Ahrs from it b4 it is flat. So the more amps you draw, the less Ahrs your battery can supply. So if you have 1 x 120 Ahr battery and are pulling 24 amps from it (C5) , you will probably only get 100 Ahrs out of it. But as you have 4 x 120 ahr and are discharging at say 24 amps, this is only 6 amps from each battery. (C20) This is the current they are rated at so if you (as recommended) only discharge to 50% SOC, then you have 60 x 4 Ahrs available (240Ahrs) So you can confidently draw 22 amps for 10 hours without stressing your batteries. However, these figures relate to Deep Cycle batteries. Yours are UPS type so it is a different story. Basically you will still get your 22 amps for 10 hours but your batteries will not last for very long. UPS batteries are designed to sit there for years (on float charge) waiting for an emergency situation and then provide power. They are not designed to be continually charged and discharged. As long as you understand the limitations of UPS batteries, they will still serve you well.

Ian
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Follow Up By: ChipPunk - Saturday, May 22, 2010 at 11:25

Saturday, May 22, 2010 at 11:25
Thanks Ian,
yes - I know too well....
And your description is good - if only batteries were linear!
And if only people could understand the significance (ie, lower loads, lower depth, longer life).

I am merely testing my UPS battery. It's 10 years old, only 38AH but is rated for my (reduction) starter's 140A draw for 1 minute to 1.60V/cell.
A recent alternator-less return home at night confirmed it still has its ~rated capacity (about 50% capacity after ~1 hour).

Normally I run dual batteries that are paralleled during charging.
Normally for similar AGMs I also have a bypass that parallels during cranking.
In this case though I want to see how long this AGM lasts....
(I must check its cycle specs - I know some UPS batteries are only rated for 6-10 cycles; others can do hundreds.)

Thanks again.
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