Still on Batteries, but New question

Submitted: Tuesday, Jan 25, 2011 at 22:24
ThreadID: 83896 Views:2583 Replies:4 FollowUps:6
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Normally I am good at maths, but help me out please. I have just bought a 120a/h deep cycle battery and have a 12 volt fridge that allegedly drags max of 2.7 amps, and there are 3 x21 watt 12v lights. I f i used all at once, how long could i expect to get out of the battery time wise if start off fully charged. Likelihood of running 3 lights at once is higly unlikely, is more likely to be running a 300w inverter off the battery along with 1 light and the fridge. I have come up withperfect scenario of 21 - 23 hrs, but realise battery will wind down to an unuseable voltage before time runs out( at least unuseable for the fridge............................................. by the way i joined as a member because of the excellent help you people have already given me.....Thx in anticipation of more help
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Reply By: oldtrack123 - Tuesday, Jan 25, 2011 at 22:44

Tuesday, Jan 25, 2011 at 22:44
Hi Kevin
your 120a/h battery has about 60a/h useful capacity IF YOU WANT IT TO HAVE A LONG LIFE

Your fridge draws far in excess of 2.7ampswhen it actually running [pumping
That 2.7A is a figure under test ,As an average continous current over 24hrs
That means depending on factors such as ambient temp,thermostat setting ,amount of time opened,amount of warm l oads.
It can draw anywhere from 40<90amphrs per 24 hrsIE from1.6 to3.75amphrs per hr
Your 3x21 watt lamps will draw alittle over 5a/hrs per hr runtime
So if you had both the lamps & fridge running you would be using from6.6<8.75 amphr per hr your battery would last from 9 down to 6.8hrs before requiring some means of fully recharging before you could start the cycle again

AnswerID: 443038

Follow Up By: kevmac....(WA) - Tuesday, Jan 25, 2011 at 23:23

Tuesday, Jan 25, 2011 at 23:23
OK then thx for that oldtrack............

So if I floated the battery across a 3 stage charger, I should be better off would I?..............led to believe the charger would be protected, once running on battery only, seeing as they tell u connect battery to charger ( normally) before powering up........ and keep lights to max of 1 x 21w globe ??
FollowupID: 715094

Follow Up By: kevmac....(WA) - Tuesday, Jan 25, 2011 at 23:32

Tuesday, Jan 25, 2011 at 23:32
sorry oldtrack but at that usage rate how long would u classify a good life for the battery, and is there steady rate of decline for increased drain? when purchased i waqs hoping on max coverage without generator of 10 - 12 hrs......... depends where u camp as to how long ya leave generator runningand apart from that we asre usually quite considerate of all other campers anyway.
FollowupID: 715097

Follow Up By: oldtrack123 - Tuesday, Jan 25, 2011 at 23:39

Tuesday, Jan 25, 2011 at 23:39
Hi Kev
If you have mains power available, then yes best leave the charger on ,
What Size is it???

Battery life is anyone,s guess but maker of battery may be able to give you some indication
They should be able to supply tables showing average life for varying depths of discharge
BUT THE SHORTENING OF LIFE IS NOT LINEAR!!!especially below discharge of 50%

FollowupID: 715098

Follow Up By: kevmac....(WA) - Tuesday, Jan 25, 2011 at 23:52

Tuesday, Jan 25, 2011 at 23:52
about to purchase a 1kva inverter generator............. using an el cheapo GMC 750w 2 stroke right now.....which floated an old battery across 3 stage charger ok for a 5 day trip just came back from....luckily were allowed to keep gens. going til 10 at night and were allowed to start at 7.30 in morning
FollowupID: 715100

Reply By: glids - Wednesday, Jan 26, 2011 at 11:20

Wednesday, Jan 26, 2011 at 11:20
You can significantly reduce the load on the battery by changing the 21W lights over to LED. I posted some details here:

I did find some of the individual LED's died in some of my lights - they do get fairly hot, and that may have contributed to this problem. To help overcome this, I have put a 3.9 ohm 1 watt resistor in the 12V feed to the two LED panels, to drop the voltage slightly - still plenty of light. If you do this, make sure you use a 1 watt resistor or it will burn out.

Hope this helps.

AnswerID: 443086

Follow Up By: kevmac....(WA) - Wednesday, Jan 26, 2011 at 13:20

Wednesday, Jan 26, 2011 at 13:20
thanks for info glids,

ex communications tech here....... so i should be able to follow ya hint re the resistor in feed ok.........sounds like good idea.......... thanks for the link
FollowupID: 715147

Follow Up By: kevmac....(WA) - Wednesday, Jan 26, 2011 at 23:43

Wednesday, Jan 26, 2011 at 23:43
heya again glids,

went and had a look at that site and a look at the ebay store as well...........ya right about the variance in pricing/ postage for the same products.........going to check out locally( in australia) first for comparisons before commiting....once again appreciate your help.
FollowupID: 715239

Reply By: kevmac....(WA) - Wednesday, Jan 26, 2011 at 15:49

Wednesday, Jan 26, 2011 at 15:49
Does anyone have any idea of the current drain of some of the basic off the shelf 12v led lights???
AnswerID: 443117

Reply By: kevmac....(WA) - Friday, Feb 11, 2011 at 17:10

Friday, Feb 11, 2011 at 17:10
Paid a visit to local caravan sales yard yesterday after finding out they were about to stock a quantity of led lamps and kits.I had made enquiries for about a week or so.Going off for short weekend away at Cosy Corner(just 35kms out of town) I am in a unit complex , so these trips are used for improvements and maintenance.I digress tho. Tried one pre set lamp of 18 LED's and is as bright as for a current drain of only 0.23 amps.Is much brighter than the standard 21w incandescantlamp. Will try to remember to take a foto to try and sho difference in brightness. Be interested to see how bright it shines in outside unit. Cost for the globe replacement locally was $24.95 so hopefully will get money's worth out of them in less drain on battery.
AnswerID: 445087

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