only just getting 12v on camper battery with car running ?

Submitted: Thursday, Jan 12, 2006 at 08:50
ThreadID: 29600 Views:2607 Replies:18 FollowUps:12
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with the 3 way fridge on in the jayco camper we can not seem to get the same volt reading as the main battery.
The set up is : main battery connected to second batt under bonnet via ARB smart seperator,6mm cable to rear of car to a 50amp anderson plug then 6mm cable from anderson plug to campers 80amp battery.
I have installed a digital volt gauge from jaycar to monitor the camper batt and on our last trip after 5 hours of driving the read out on the camper was 11.7V,all i can think is the 3 way fridge on 12v is using more power than can be supplied through the 6mm cable from the second batt to the camper. when i saw ths low read out i checked the batts under the bonnet and both around 14V.

any thoughts?
cheers.
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Reply By: Redback - Thursday, Jan 12, 2006 at 09:04

Thursday, Jan 12, 2006 at 09:04
3 ways suck alot of power 12 to 16 amp hour so it's probably for that reason that your reading is not the same, still it should be higher than 11.7 after a 5 hour drive, look at the cable it may not be a true 6mm it may only be 2 or 3 inside diameter and 6mm outside diameter, and your voltage drop is the cause, we got 6mm cable on ours but i made sure the inside diameter was 6mm the wire itself less the insulation.

Oh i'm no expert this is only a guess.

Baz.
AnswerID: 147961

Follow Up By: Mainey (WA) - Sunday, Jan 15, 2006 at 20:52

Sunday, Jan 15, 2006 at 20:52
6mm cable is way too skinny...

For sure it will give you voltage loss, because the 3way luv's to suk heaps of power off 12v, and you'l find it will heat up the 6mm cable, indicating voltage loss!!

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FollowupID: 401977

Reply By: Notso - Thursday, Jan 12, 2006 at 09:04

Thursday, Jan 12, 2006 at 09:04
Sounds like too much resistance in the power supply cable.

The three way will draw about 10 amps or so off the line on 12 volts

Check out this link. It is fairly long winded but eventually gets to the point.

http://www.fridge-and-solar.net/wire.html
AnswerID: 147962

Reply By: Vince NSW - Thursday, Jan 12, 2006 at 09:14

Thursday, Jan 12, 2006 at 09:14
I had the same problem about 2 years ago. Found that it was the earth return to the car. Put in bigger earth and fixed the problem.
Do you have 6mm neg via the anderson plug ?
Vince
AnswerID: 147964

Reply By: time waster - Thursday, Jan 12, 2006 at 09:18

Thursday, Jan 12, 2006 at 09:18
yes vince i used the narva two core heat shrunk 6mm positive and neg
AnswerID: 147965

Reply By: Penguin (NSW) - Thursday, Jan 12, 2006 at 09:48

Thursday, Jan 12, 2006 at 09:48
I have an almost identical setup to yours in the L/C and I'm getting about 12.2 V at the fridge. I guess it's a function if the length and gauge of cable run from the car battery to the fridge.

There are methods of calculating voltage drop over a given length of cable.
Try this one.

Mike
AnswerID: 147972

Follow Up By: time waster - Thursday, Jan 12, 2006 at 09:57

Thursday, Jan 12, 2006 at 09:57
Penguin, if we start off in the morning withe the camper on mains it reads 13.7v and when hitched and car running about 12.8v but during the drive the battery is slowly loosing charge as we drive and thought anything under 13v will not charge the battery. so i assume yours at 12.2v will not get a full charge either?

christian
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FollowupID: 401277

Follow Up By: Penguin (NSW) - Thursday, Jan 12, 2006 at 10:09

Thursday, Jan 12, 2006 at 10:09
Christian,

I should have explained my setup in more detail. I installed the separate 6mm cable purely to increase the voltage at the 3 way fridge. I have solar and a separate battery charger to maintain the battery.

I misunderstood your question. Jayco also puts a diode in the charge circuit to prevent the fridge from using the house battery. There's 0.6V drop for a start. I would suggest solar or something like an Arrid Twincharge in the trailer to properly charge your battery. Check out All About 12 Volt. They're a bit expensive but work really well.

Mike
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FollowupID: 401279

Reply By: Darian (formerly Banjo) - Thursday, Jan 12, 2006 at 09:57

Thursday, Jan 12, 2006 at 09:57
Not sure if you are testing while running - just a quick point from my recent learnings on that subject area - gotta have the whole lot running when checking voltage levels and drop in cables etc. Re batteries - I think the experts suggest that a group of healthy, charged batteries can all have different voltage levels at rest, for various technical reasons. The camper battery probably never gets the same boot as the front units - and it'd need to be the same type as the front ones, for the comparison to be valid.
AnswerID: 147974

Follow Up By: time waster - Thursday, Jan 12, 2006 at 09:59

Thursday, Jan 12, 2006 at 09:59
yes i tested all while running
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Reply By: Leroy - Thursday, Jan 12, 2006 at 10:00

Thursday, Jan 12, 2006 at 10:00
I'd be heading down to Jaycar and looking at some 4awg cable. It's think like your little finger. Run both + and - cables. Don't rely on the car body for the earth return and you should find there is minimum voltage drop. Also keep using anderson plugs.
what is the voltage measured with the fridge disconnected?

Leroy
AnswerID: 147975

Follow Up By: time waster - Thursday, Jan 12, 2006 at 10:11

Thursday, Jan 12, 2006 at 10:11
i will check with fridge disconnected i think i did do that and it was around the same as main,thats what makes me think theres not enough juice flowing down the cable when the load is on.
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FollowupID: 401281

Follow Up By: Leroy - Thursday, Jan 12, 2006 at 12:31

Thursday, Jan 12, 2006 at 12:31
I just read your reply to a post further up about the voltage decrreasing as the day goes by. It could be that the cabling is too small and as you a drawing current the cable heats up, increases resistance and hence the voltage drop.
Secondly. check the cables between the batteries and the isolators. Could be a bad connection or crimp on a connector. It's like the secondary battery is not being charged while it's under load.

Leroy
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FollowupID: 401295

Reply By: dags666 - Thursday, Jan 12, 2006 at 10:13

Thursday, Jan 12, 2006 at 10:13
just wondering how hot was it outside and was you fridge and contents chiiled down before you left hme on your 5 hour journey. i have learned over the yers before a trip chill all content down at least 2 days before or longer on 240 if possible or if you load up the frige with hot gear it wiil sux the guts out of your batteries no matter how good your set up is good luck dags
AnswerID: 147981

Follow Up By: time waster - Thursday, Jan 12, 2006 at 10:15

Thursday, Jan 12, 2006 at 10:15
outside was mid 20's and the fridge had been on for two weeks
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FollowupID: 401282

Follow Up By: Mike DiD - Thursday, Jan 12, 2006 at 10:28

Thursday, Jan 12, 2006 at 10:28
Most 3-way fridges have no Thermostat on 12 volts - whenever they are plugged in they are drawing 10 amps.

Mike
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FollowupID: 401285

Reply By: Keith_A (Qld) - Thursday, Jan 12, 2006 at 10:14

Thursday, Jan 12, 2006 at 10:14
Have you looked at Collyn Rivers Site - very thorough explanation of all things electrical, with a special section on auto wiring to fridges :

From the main page, select 'Fridges - making them work -Part 2'
http://www.caravanandmotorhomebooks.com/articles/index.htm
regards................Keith

AnswerID: 147983

Reply By: Mike DiD - Thursday, Jan 12, 2006 at 10:59

Thursday, Jan 12, 2006 at 10:59
Assume there is 8 metres from Main Battery to CT Fridge (or Battery) so you will have 16 metres of wire (supply and earth). If it is 8Ga (4mm diameter of copper) then you will have 16 x 0.0025 ohms = 0.04 ohms. Assume an additional 0.02 ohms across connectors and fuses. Total 0.06 ohms

So at 10 amps you will have a voltage drop of 0.6 volt between Main Battery and CT Fridge (or Battery). If your Alternator can maintain 14.2 volts at the Main Battery, then you will have 13.6 at the CT - enough to maintain charge or slowly charge any battery.

Mike
AnswerID: 147992

Reply By: desert - Thursday, Jan 12, 2006 at 11:57

Thursday, Jan 12, 2006 at 11:57
It's almost certainly a voltage drop problem over the distance. Easiest fix is to "twin" the supply cable to the van, ie run another cable the full circuit and solder both cables at each junction. 3-way are heavy power consumers and are only marginal units on 12v DC. However, they are best on LPG and after all that is what they were designed to do.
AnswerID: 148004

Reply By: tonysmc - Thursday, Jan 12, 2006 at 15:56

Thursday, Jan 12, 2006 at 15:56
Time waster, not really solving your problem, however can I suggest not having the fridge on 12 volt when driving. I reason I say this is that for a 3way to work it has to be level and you will find that as the car is moving it will not be level long enough for the evaporation process to work, thus drawing power for nothing. I would just make sure it is a cold as you can get it overnight and when you hit the road turn it off and it will be like an esky. I am sure if you do a search on 3ways you will find this elsewhere.
As for the battery, years ago I had a similar problem with the deep cycle as the Aux and was told it was because they only accept a charge at a slower rate they need a long time (more than 5 hours driving) to get full once they have gone right down. I now only use starter batteries with a low voltage cut out and have never had a problem.
Cheers Tony.
AnswerID: 148065

Follow Up By: Crackles - Thursday, Jan 12, 2006 at 17:54

Thursday, Jan 12, 2006 at 17:54
Tony the 3 way will work fine on 12 volt when driving. It's only when left stationary on an angle where they stop working.
Cheers Craig........
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FollowupID: 401365

Reply By: Noosa Fox - Thursday, Jan 12, 2006 at 17:41

Thursday, Jan 12, 2006 at 17:41
When most people quote 6mm cable they are meaning that the cable is 6 square mm of area across it, and the actual diameterof the cable is only about 2mm./

In my vehicle we have 6mm diameter wire for both positive and negative and if the vehicle batteries are showing 14 volts the voltage in the van will be 13.8 or 13.9 volts. Our terminals are soldered.

I think most likely cause is undersized cable or poor connections at one or more of the joints.

Brian
Brian
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AnswerID: 148092

Reply By: Member - Charlie M (SA) - Thursday, Jan 12, 2006 at 18:03

Thursday, Jan 12, 2006 at 18:03
Run 8mm cable. This is the size I run on my trailer and caravan for charging batteries though anderson plug. No Problems with running 3way electrolux caravan fridge on 12volt.
Cheers
Charlie
AnswerID: 148099

Reply By: ACDC - Thursday, Jan 12, 2006 at 18:47

Thursday, Jan 12, 2006 at 18:47
You must use at least 8mm wire to charge a battery in a van.
Jayco now use 2/ 6mm wires one for fridge one for battery.
AnswerID: 148114

Reply By: Rocky_QLD - Thursday, Jan 12, 2006 at 18:47

Thursday, Jan 12, 2006 at 18:47
Hi TW

We have our 50l chestcold mounted in a custom made box on the draw bar, fridge runs on gas even when travelling heat is removed by one of those whirly thingos mounted directly over the chimney. Fridge sits on a slide for access and removal and yes it is all legal checked and approved by a gas guy
AnswerID: 148115

Follow Up By: ACDC - Thursday, Jan 12, 2006 at 19:58

Thursday, Jan 12, 2006 at 19:58
Anyone who runs there fridge on gas while travelling is crazy,not to mention illegal!!
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FollowupID: 401390

Follow Up By: Noosa Fox - Thursday, Jan 12, 2006 at 22:00

Thursday, Jan 12, 2006 at 22:00
I agree with ACDC.

It may well be legal to have the fridge there and set up properly by a gas man, in the same way as that fridges are set up in caravans are legal. But it is Not legal to operate them on gas when moving.

When you go into a servo and there are petrol vapours coming from the car next to your draw bar and the hole thing goes up with a big bang, try telling that your your insurance company, and the police and fire brigade who attend.

Sounds like a good way to donate everything you own to the people you have to compensate for your actions, if you have survived the explosion that is.

Brian
Brian
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FollowupID: 401422

Reply By: eerfree - Thursday, Jan 12, 2006 at 21:55

Thursday, Jan 12, 2006 at 21:55
TW
Just a thought,the cable has been Soldered into the Anderson plugs hasn't it crimping has its problems!!!

eerfree
AnswerID: 148172

Follow Up By: time waster - Friday, Jan 13, 2006 at 07:59

Friday, Jan 13, 2006 at 07:59
Thankyou all for your helpfull replies,yes i have soldered all connections.When i was in getting some more so called narva 6mm cable if you look on the drun in small print it actually says 4.65mm2 .
I also run another wire + - from c/t batt to 3 way,3.5m length,the fridge end went from 12.00v to 12.27v. Will now run another length the whole way from second batt to c/t so in real terms it should be 9.3mm2 in cable size then.
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FollowupID: 401470

Reply By: Member - Collyn R (WA) - Friday, Jan 13, 2006 at 13:50

Friday, Jan 13, 2006 at 13:50
Three-way fridges draw 10-12 amps. The existing 6 mm cable is hopelessly inadequate. To do this job properly you breally need to use two twin 8 mm cables. Parallel each cable to give you twon by 16 mm. Overkill? Not if yoiu want that fridge to really perform as intended.
Trust this helps
Collyn Rivers
AnswerID: 148298

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