So I've been using a friends Toyota Hiace Campervan (1989, high roof)
I've just upgraded to a 105Ah battery from a 65Ah

Solar charging works as expected, but the charging from the main or alternator isn't doing enough to keep it topped up.

When the ignition is on (before the engine has started, but the accessory signal is active), it closes a solenoid which connects the main battery to the auxilliary through this little device, which I think is supposed to be a current limiting resistor.

As I said the vehicle is super old, and I would like to improve the charging system when the vehicle is running. I've attached some photos of this small device, but if I short that device and bypass it, the second battery charges up nicely.

The amp and head unit run from the aux battery so the vehicle can be off and solar panels can keep the tunes going, but even when I am driving now the aux battery is getting down to 12.0V, I am drawing about 4 amps from it using the audio system so that's a bit but the alternator should be able to supplement that. Can someone explain what this device is?

Resitance across terminals is about 0.2 - 0.5 ohm, but with a multimeter probe, which has less of a good connection than the ring terminals from the battery, so I would expect it to be even less and was is the point in it? But shorting it works!
 
TL;DR
What is this little device from the 1980s that is between my main and aux battery in a campervan?

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Last edited:
It looks like it might be a thermal overload, a bimetal strip that lifts if it gets to hot.
can you lift one side off the contact or is it welded both ends?
 

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Thread Information

Title
Old Campervan Aux Battery Charging components, what is this thing!?
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Auto Electrician Forum
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Created
tombola123,
Last reply from
westward10,
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