Amp Hrs on 2nd Battery

Submitted: Thursday, Jan 13, 2005 at 11:44
ThreadID: 19322 Views:4190 Replies:11 FollowUps:3
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just got a new 2nd battery from a mate.. it has 55 Amp hour capacity..
can forumties please confirm that is has enough power to use for powering Engel 40L and Flouro Light for 2-3 day trips?
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Reply By: geocacher (djcache) - Thursday, Jan 13, 2005 at 12:04

Thursday, Jan 13, 2005 at 12:04
You have a PM.

Do you have a means of charging while you are away? More information is needed really.

Is it a small deep cycle battery or a 55Ah starting battery?
Do you have a dual battery system, solar setup or similar?
If it's not permanently mounted yet is it going to be? A wet cell that tips over on a rough track makes a hell of a mess, not to mention the damage it causes.

Dave
AnswerID: 92780

Reply By: MrBitchi - Thursday, Jan 13, 2005 at 12:06

Thursday, Jan 13, 2005 at 12:06
Depends how often you charge it. 55ah means it will supply 55 amps for one hour or 1 amp for 55 hours. Engel will draw about 3amps, fluoro about 1 amp. Therefore Engel and fluoro will draw ~4 amps and your battery will last about 13 hours straight running. Fridge on it's own will flatten the battery in around 18 hours.
Wont go into the niceties of not completely flattening a battery and shortening it's life. Suffice to say it will need a good charge each day or you'll end up with warm beer....:--(

Most forumites seem to use 100 or 150 ah batteries. Mines 100 and it works OK for me running my Waeco and flouro.
Cheers, John.
AnswerID: 92781

Follow Up By: Wok - Thursday, Jan 13, 2005 at 18:05

Thursday, Jan 13, 2005 at 18:05
Hello John,

Batteries don't discharge as you suggest..its not a 'straight' conversion.
Have a Google for ' Peukert's Law ' .

cheers
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FollowupID: 351790

Follow Up By: MrBitchi - Friday, Jan 14, 2005 at 08:38

Friday, Jan 14, 2005 at 08:38
Understand that, Wok. Was just applying the KISS principal...:-)
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FollowupID: 351902

Follow Up By: kiss'n'dirt - Friday, Jan 14, 2005 at 12:01

Friday, Jan 14, 2005 at 12:01
sorry to disappoint youb but all batteries only have a useful operating GAP of 80% of it's rating. so your 55amp/hr battery can only be drained of 44 amps. ideal is to only drain a battery to 50% of its capacity.

the battery is literally FUBAR at 80% and it'll take 6-8hrs to recharge to it's full capacity if it's a wet cell deep cycle. i hope you have another battery or buy a new one that's an AGM battery. your lifeline and optimas are the best but cheaper alternative are remco and fullriver. a Fullriver AGM battery at 120a/hr is rrp $380. i recharged 70 amps in 20 mins from a GU patrol. i ran a 60lt waeco as a freezer for meats and making my own ice. it used 65amps in 13hrs plus another 5 amps for a 12v light.

i drove everyday to keep the battery charged
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FollowupID: 352006

Reply By: Member - Mozza (NSW) - Thursday, Jan 13, 2005 at 12:07

Thursday, Jan 13, 2005 at 12:07
i have a dual battery system mounted in engine bay
it is a deep cycle
AnswerID: 92782

Reply By: Member - Ross P (NSW) - Thursday, Jan 13, 2005 at 12:16

Thursday, Jan 13, 2005 at 12:16
55 AH Rating if 100% charged!
If charging from motor vehicle alternator/voltage regulator experience suggest you wil be only able to achieve 80% (some say 70- to 75%).
Prudent use of the battery to achieve reasonable life suggests don't discharge below 50%.

Therefore, useable capacity is only 55 times 30% or 16.5AH.
If you charge to 100% before you leave home using a mains powered smart multistage charger this numbber increases to 27.5 AH.
Good quality fluros draws about 1 amp say. Assume when you say 2 to 3 days you mean 3 nights. Say light for 4 hours per night equals 12 AH.
If you are not recharging by driving or other means you're OK for lighting but not the fridge.
If you assume that the fridge will be running for say 48 hours without auxilliary charging ie driving to and from, and assume the Engel draws on average 1Amp (others will have a more accurate figure for a 60 Litre Engel) you need 48 AH
So my calculations say you need at least 60 AH of useable battery capacity for fridge anmd light if you can't recharge while your camped..

AnswerID: 92784

Reply By: Wok - Thursday, Jan 13, 2005 at 18:40

Thursday, Jan 13, 2005 at 18:40
Mozza,

If your 55Ah is the C20 discharge rate you won't have a 55Ah battery if you use the Engel [if its current draw is higher then 2.75 amps per hour] It needs to be derated with Peukert's Law. The situation isn't so bad if the battery is a Gel or AGM [lower losses]

cheers
AnswerID: 92859

Reply By: Crackles - Thursday, Jan 13, 2005 at 18:49

Thursday, Jan 13, 2005 at 18:49
Simply........No. Not with out additional charging. With days around 30 degrees & not starting your car for 2 nights you would need at least a 115 amp hour battery to even get close.
The 55 AH portable batteries I have seen will run a fridge for about 1 full day. (Note:There are many variables in how long they will go)
Cheers Craig............
AnswerID: 92861

Reply By: Brew69(SA) - Friday, Jan 14, 2005 at 07:38

Friday, Jan 14, 2005 at 07:38
I have a 55amp deep cycle aux battery which runs a waeco FF-70. Whilst in cooler weather i have had no troubles with 2 day stays, when it heats up........forget it. Less than 24 hours! I am going to take my genny on any long stop trips. As far as driving and one night stops,you would be fine.Why do u only have a 55a/h? Only reason i do is there is no room with all the lpg crap under the bonnett for anything bigger.
AnswerID: 92934

Reply By: Member - Sand Man (SA) - Friday, Jan 14, 2005 at 08:26

Friday, Jan 14, 2005 at 08:26
Mozza,

I'm going to throw something else into the debate which is somewhat different to other's input.

First of all, the fridge once cold, will not run all the time, but cycle. Therefore current draw is reduced. Remember the more recent Engel 40 litre fridge draws 2.7 amps MAXIMUM.

Secondly, you could turn the fridge off altogether at night, as there is very little heat load and the fridge is not being opened.

So I'd say you should be all right.

I had a 77 ah wet deep cycle auxilliary battery and could safely run the fridge for 3 full days without recharging. (I have a volt meter connected which gives me an idea of remaining battery voltage)

I have recently changed over to a 55 ah Gel deep cycle battery and still don't envisage any problems, but I guess time will tell.
Bill


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AnswerID: 92941

Reply By: Member - Toonfish - Friday, Jan 14, 2005 at 21:23

Friday, Jan 14, 2005 at 21:23
dont forget that most compressor fridges run on a %30 duty cycle so obviously the fridge isnt running all the time (compressor only fan may ).
so put this in to the equation.
having said that my 40 ah gel cell deep cycle was fine for 4 days last x-mas running a cf 50 compresssor a 1ah fluoro and a el cheapo shower and we simply plugged the frudge back in to the car rear socket (blue apple switched ) and was still fine in moderately hot weather and as i did you can set the gelcell up on a regulated charging system on the cheap if room is an issue in the engine bay i just purchased a marine box and two 10 amp cig lighters fused and fitted with a regulator. done me for 12 months till i got the dual bat finally fitted.
or just charge the battery before leaving and run of this only when car isnt running .
SIMPLE
doesnt have to cost the earth or look shmick!
AnswerID: 93134

Reply By: Mainey... - Saturday, Jan 15, 2005 at 10:41

Saturday, Jan 15, 2005 at 10:41
(Quote) just got a new 2nd battery.... 55 Amp hour capacity..
can forumties please confirm that is has enough power to use for powering Engel 40L and Flouro Light for 2-3 day trips (end quote)

Yes, .. IF the battery is connected to the vechicle alternator for recharging.

No, .. if you expect it to last 3 days as a stand alone system.

AnswerID: 93211

Reply By: Member - Mozza (NSW) - Monday, Jan 17, 2005 at 08:20

Monday, Jan 17, 2005 at 08:20
just a follow-up on the 2nd battery issue.
swapped the 55amp hr for a 80 amp hour.. setup under bonnet which charges via an isolator whilst driving. will be checking out how long it lasts in a couple of weekends on trip Myall Lakes (if anyone is interested?!)
problem solved!
AnswerID: 93518

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