SSD relay - or how to charge 2 batteries at one time

It seems that could depelete the engine battery if left connected while the house battery is depeleted.

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  When I tried casting out nines I made a hash of it.
Reply to
Jasen Betts
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It could...

I did not mention that, in addition to that, I designed a low-volt cutout device (741 and relay) for our caravan. It also had a changeover switch for choosing between car and local aux battery. I forget if the low volt cutout was only active on the car circuit or whether it protected both.

You can buy such devices ready made...

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Reply to
Tim Watts

A little update

I have my test now, using a 7660 to pump the gate voltage and a IFT3205 MOSFET. This works well. I have a analog volt meter attached to the axial battery, so I can see what it happening. When the engine is running, the original relay is on, the voltage is jumping, it is not stable, but still charging. Trying a diode, short circuit and my FET are all much more stable solutions - the voltage becomes stable. I should add that my FET solution is controlled by the power to drive the relay (I wonder whether that could be the problem) Simply measuring the charge is 2.7A, using the relay or my FET it is 2.4A It would be higher in case the battery would be more empty.

In a change in design I could add a schottky diode to avoid flow from leisure to main, or a double FET, 2 FET's in opposite direction. The second is not needed for this but could come in handy some day. I will try this for some time, just the FET, and see how it works.

Reply to
Sonnich Jensen

Fully charge the main battery. Fully deplete the leisure battery. Close the switch between them. What's the peak current? Can the FET handle that?

This makes interesting reading for automotive electronics.

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Reply to
Mike

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