Maplin deep cycle solar batteries

[Nix]

RS - with all due respect, you've got little in the way of power concepts. I suspect the only way you are going to get an inkling is to go ahead and buy the 125ah battery, connect a 12v inverter to it and give it a full 1kW load. Then you can report back with how long it lasted, along with which fuses blew before it melted which cables & connections, ok?

I STRONGLY recommend you do NOT do this!

Why not come over to our next meet and I can demo a set up for you?

[River Song]

Thanks for that/ Sadly I can't make any RV as it would blow my personal OPSEC completely out of the water

I'll look at this further. and probably take piccys as I go along.
Watch this space

[LawAbidingCitizen]

(1 November 2013, 21:00)Nix Wrote:

Quote:It means it should put out a maximum of 125 amps for an hour. If you use all of the 1KW from the inverter this should be around 4 amps output if my calculations are correct (1000 watts / 240 volts = 4.16 amps). Which means your battery should last about 30 hours (125AH / 4 amps = 31.25). However this is seldom the case as there is a degree of redundancy involved so it's best to take off about 30%. Therefore your 125AH battery is really about 87.5AH (87.5AH / 4 amps = 21.875), so in reality it should last about 20 hours. One thing though is you shouldn't really completely discharge to battery and it should not be allowed to go down below about 30% before recharging, so taking taking that 30% off as well we have - 61.25AH / 4 amps = 15.31 hours, so you will need to recharge the battery after about 15 hours use at a maximum of 1 KW (4 amps).

LAC, your intentions are good but the calculation is way out. If you use 1kW power on a single 12v 125ah battery, you're looking at a very short time indeed.

Firstly, it's 1kW/12v = 83 amps! Not only will you have to use massive cables to carry the ampage (you could just get away with 16.0mm, depending, but I'd use 25.0mm personally).

Secondly, using 1kW, I reckon the battery would last you 3 mins max before you start endangering it's DOD life span.

Quite right, these batteries are designed for slow discharge and not an abrupt drain from huge loads.

I know I realised that after I sent it, forgot that it was inverted to 240 volts ac

[Nix]

(2 November 2013, 11:47)River Song Wrote: ...Sadly I can't make any RV as it would blow my personal OPSEC completely out of the water...

You could come as the Mysterious Masked Marauder and we'd never know your true identity but perhaps the hair dryer in one hand and Harveys Bristol Cream in the other might give it away...

[Skvez]

(1 November 2013, 21:47)River Song Wrote: I don't need a 1kW inverter to charge a USB phone. My 150W one will do that thanks..

If you're using USB it's limited to 5V at 1A (5W) and it's waseful to convert 12V d.c. to 230V a.c. just to convert it back to 5V d.c.

(1 November 2013, 21:47)River Song Wrote: What is the point in purchasing a 1KW inverter if you can't use it?

A 1kW inverter is useful for some loads (such as motors) that have a very large starting surge. It is also useful in cases where you have many batteries wired in parallel.

The "cigarette lighter" output on a car is usually limited to 10A @ 12V = 120W

Most batteries Ah rating is based on a discharge over 20 hours. So your 125Ah is implying 6.25A for 20 hours to totally discharge your battery (which will ruin it). Taking it down to 75% charged means you can draw 6.25A for 5 hours.
You should be thinking more along the lines of
6.25A @ 12V = 75W for 5 hours
or
10A @ 12V = 120W for ~3 hours
You can certainly run your hair dryer from this (I'd like to think you can dry your hair in a few minutes) but the cooling device for the Harveys Bristol Cream is more of a problem as it needs to run about 8 hours a day.

[Nix]

Personally I keep to a maximum discharge of around 25 - 30% to give the batteries a much longer life although I've read that the maximum efficiency for a working battery is 50% DOD. One day I'll experiment with the 50% figure. Even though my battery discharges are more shallow, it's good every now and then to go lower. Apparently extremely shallow discharges aren't good for the batteries and they must have the odd deeper discharge.

[Skvez]

(5 November 2013, 09:42)Nix Wrote: Personally I keep to a maximum discharge of around 25 - 30%

That was what I meant:
Discharge to 75% i.e. discharge by 25%