caravan wireing soleniod spyke

Submitted: Tuesday, Feb 12, 2008 at 00:03
ThreadID: 54492 Views:1684 Replies:2 FollowUps:4
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hi all i need some advice . i plan on running power from my batterie to my caravan fridge. this will involve a solenoid that will turn on during traveling and when parked turn off. the question is when the solenoid turns of will it spike my batterie? i have heard during dual batterie setup a spike device is needed . will i need one for this setup ?
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Reply By: jeepthing - Tuesday, Feb 12, 2008 at 08:40

Tuesday, Feb 12, 2008 at 08:40
I don't believe there will be any spike. I bought a solenoid charging kit for my camper from Derek of Affordable Batteries and there was no spike protection included. The solenoid activates when the charging system reaches 14 v I think it it and turns off when the primary vehicle battery drops below a certain voltage.

Pretty sure he advsertises on this site his web address is The kit is simple to connect and reasonably priced if you haven't already got one.

I also bought his dual battery set up kit again I don't believe there was any spike protection as I don't believe one is needed due to the way the system works. I'm sure Derek wil advise you anyway I've always found him to be very obliging and happy to give advice.

AnswerID: 287012

Reply By: Member - Mike DID - Tuesday, Feb 12, 2008 at 16:50

Tuesday, Feb 12, 2008 at 16:50
Your starter motor draws 200 amps and is a very inductive load. When this current is interrupted there will be a massive back-emf surge.

I have no idea why people think that connecting/disconnecting two 12 volt batteries will cause a surge anywhere near that big.

Just another example of Battery Isolator marketers trying to come with "you must buy this one" features.
AnswerID: 287076

Follow Up By: BMKal - Wednesday, Feb 13, 2008 at 03:36

Wednesday, Feb 13, 2008 at 03:36
Yes and it is exactly this back-emf surge that will cause damage to a fridge if not connected via a solenoid or some similar protection.

You might get away with it for a while - I did - for a while. But in the longer term, the cost of a correctly set up solenoid in the wiring sytem is cheap compared to replacing the compressor in your fridge.
FollowupID: 552359

Follow Up By: Member - Mike DID - Wednesday, Feb 13, 2008 at 07:33

Wednesday, Feb 13, 2008 at 07:33
I don't understand - you're saying all the electronics in a car survive the surges, but the back emf from the starter motor will eventually kill the fridge ?
FollowupID: 552364

Follow Up By: Mike Harding - Wednesday, Feb 13, 2008 at 08:13

Wednesday, Feb 13, 2008 at 08:13
Best of luck Mike.
FollowupID: 552367

Follow Up By: Member - Olcoolone (S.A) - Wednesday, Feb 13, 2008 at 18:20

Wednesday, Feb 13, 2008 at 18:20
EMF happens when a solenoid or relay disengages causing a backward voltage rush from the coil.

FollowupID: 552487

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