Max amperage usage without damaging batteries

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).

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.

Well said Carlsp. Daryl

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

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

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.

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 :-)

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.

Sounds like a good system that can handle the anticipated load. Though a week of rain may change the situation. :)

Andrew

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 !!!

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

Please don't be sarcastic....

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 ?

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.

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...)

C10

Ian

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).

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

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.