DC-DC Charger with cross-over switch

DIY
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1

Greetings,

Looking for some advice on installing a DC-DC charger between my house and start battery. My current setup up has my alternator charging my AGM house battery directly. The AGM start battery must be manually connected to the alternator through a cross-over switch for charging or for added starting capacity from the house battery. I would like to install a DC-DC charger between the house and start batteries so I can maintain the start battery without manual intervention. The first picture shows my current setup. Note that I have removed grounds/fuses etc. in the picture for clarity.

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I would like to install the DC-DC charger as shown in the second picture:

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I would like to maintain the cross-over switch as shown for emergency situations, but I am wondering if there is any issue with the DC-DC charger having the input and output both tied to the house positive terminal when the cross-over switch is closed? Hope this makes sense and the pictures come through. First time posting here!

Thanks in advance for any input.

2

Use an automatic charge relay instead. These can also come with a manual switch input for emergency starting.

you really only need a dc/dc where there is a change of voltage required.