Car fridge 240v reverse charging battery...

Submitted: Monday, Apr 21, 2014 at 23:24
ThreadID: 107393 Views:3215 Replies:7 FollowUps:1
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Hi all,

Getting ready for camping over the next couple of days thought I'd give my dual battery (deep cycle century N70t) a top up with the charger. After checking it noticed a fizzing noise coming from the battery. Checked Dr Google and this can be normal, but charge was finished so removed the charger. Checked again when closing the bonnet and still fizzing.

I have a Primus 60lt fridge which takes 240v, 12v or 24v. There are two plugs. During this my Primus fridge was plugged into both 240v and the battery. According to the instructions the fridge then selects the 240v rather than running off the battery. Got out the multimeter to check the second battery voltage, and noticed my redarc SB12 was flashing indicating reverse charging. Measured the voltage on the second battery and up to 15v (hence the fizzing sound).

Anyway, worked out that the 240v to 12v transformer inside the Primus must be sending charge through the 12v side and back into the battery. Disconnected the 12v lead from the Primus and noise stopped then battery voltage dropped down to 13.2v.

Assuming this is not normal - not sure how long this has been happening. Any suggestions to fix? Diode on the 12v inlet? Can install a switch on the 12v near where I plug the fridge in.

Any advice appreciated.

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Reply By: Michael ( Moss Vale NSW) - Tuesday, Apr 22, 2014 at 00:27

Tuesday, Apr 22, 2014 at 00:27
I would be asking the retailer you bought it from. Let them do the thinking. Is it still under warranty? It's obviously not as it should be. I suppose having only one power source connected will get you out of trouble but when it starts affecting your battery, It obviously can be dangerous. Michael
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AnswerID: 530994

Reply By: Ross M - Tuesday, Apr 22, 2014 at 08:08

Tuesday, Apr 22, 2014 at 08:08
Although the fridge will operate from various sources of electricity, there should be some feature which prevents two sources being operational at the one time.

Does the instructions for the fridge mention about disconnecting one source BEFORE connecting another?
I would think it does. Then as the operator, you have to make only the correct connections for the situation. Then there should be no problem.
AnswerID: 530997

Reply By: oldtrack123 - Tuesday, Apr 22, 2014 at 09:02

Tuesday, Apr 22, 2014 at 09:02
The instructions are not very clear
They apppear to say it is ok to have both sources connected & it will Auto select 240V when avaiable
'BUT elsewhere they say to monitor battery voltage to prevent over charge

. Which ever it is It is not very satisfactory !

There should be automatic seperation so ONLY one source can be in operation at any time
Best Contact Primus for direct confirmation on how it should be used!!

AnswerID: 530999

Reply By: pop2jocem - Tuesday, Apr 22, 2014 at 09:25

Tuesday, Apr 22, 2014 at 09:25
Not sure about the latest offerings but my Engels, one, 40 lt and about 16 years old and the other an inherited 1985 or thereabouts 29 lt obviously 240v/12v like the rest have different cables to select the power source. There is a little slide doodad that stops the connection of both at the same time. Because of where I have one of them mounted in the vehicle it was a bit of a chore to remove the 12v and connect the 240v.
Although I would only have one power source connected at a time I often wondered what if any dramas could happen if I removed said doodad (don't you love them technical terms) and left both plugged in to the fridge. I have never tried to do that because of the possibility of damage but it appears Mr Engel and maybe Mr Primus consider that connection of both as a big no no. I would have thought that this being the case, some provision would have been made to prevent such an occurrence.

AnswerID: 531001

Reply By: Member - John and Val - Tuesday, Apr 22, 2014 at 09:27

Tuesday, Apr 22, 2014 at 09:27

Doesn't sound healthy! I doubt that your fridge is intended to send charge to the battery. Also the flashing Redarc SB12 is a concern - suggest check just what message it's sending you here.

I'd avoid adding a diode to the 12V fridge line to prevent current flow from the fridge to the battery. It will cause voltage drop - if you do go up that path I'd recommend using only a schottky type to minimise voltage loss - I think Jaycar have a 10A one.

Good luck!

J and V
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AnswerID: 531002

Reply By: HKB Electronics - Tuesday, Apr 22, 2014 at 14:30

Tuesday, Apr 22, 2014 at 14:30
Take the fridge back, it is faulty, the 12V input should be isolated when running on 240V
to prevent the internal power supply being overloaded should the 12V plug be left connected to the car.

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AnswerID: 531013

Reply By: TomHo - Wednesday, Apr 23, 2014 at 06:46

Wednesday, Apr 23, 2014 at 06:46
Thanks for the advice. Both leads have separate inputs so have just disconnected the 12v when it is plugged in. It's still under warranty so will take it back once I have finished this weekend. I am sure this is a recent fault as had many trips where both were plugged in with no issue.

BTW noticed HKB had replied. Got an alternator booster delivered last Thursday to install on my Prado and works perfectly, so thanks!



AnswerID: 531045

Follow Up By: HKB Electronics - Wednesday, Apr 23, 2014 at 16:06

Wednesday, Apr 23, 2014 at 16:06
No problem, happy motoring:)


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