Be careful charging your starter battery if you have an auxiliary battery

[Numb Thumbs]

Something I had not thought of...


While I have been in lockdown, the car has sat in the garage, unused. I have charged the starter battery a couple of times now with a battery charger because it was getting down - the various computers in the car use a small amount of current and it eventually will flatten the starter battery.
I saw a YouTube video today that points out a potential problem with doing this if you have a permanent auxiliary battery in the car:


YouTube (https://www.youtube.com/watch?v=rDXixCzg6iw)

https://www.aulro.com/afvb/image/gif;base64,R0lGODlhAQABAPABAP/wAAACH5BAEKAAAALAAAAAABAAEAAAICRAEAOw==
If you connect a charger to your starter battery without disconnecting the auxiliary battery, you may inadvertently flatten the starter battery. If you have a DC-DC charger on the auxiliary battery, it will sense the jump in Voltage at your starter battery when you connect the charger. It will then start draining current from the starter battery to charge the auxiliary battery. If your DC-DC charger is rated at a higher Ampage than the 240 Volt charger you are using to charge the starter battery, you will actually be flattening the starter battery, not charging it because the DC-DC charger will be draining more Amps out of the starter battery than the 240 Volt charger can put into the starter battery.
Something to think about...


Cheers
Numb Thumbs ;)
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[PhilipA]

If you connect a charger to your starter battery without disconnecting the auxiliary battery, you may inadvertently flatten the starter battery.

Most if not all DC/DC chargers that I have investigated will go into float with a LA or AGM battery once the auxiliary battery is fully charged and turn of if a Lithium battery is fully charged.

So you would have to have either a flat auxiliary battery for this to happen or a very small charger.

BTW many DC/Dc chargers have an ignition feed .

I call Fake News.

[p38arover]

I find it hard to watch his videos. In fact, I usually give up after a few minutes. Too much hand waving for me - but he's nowhere near as bad as Scotty Kilmer whose hand waving and terrible videography makes him impossible to watch.

[Tombie]

There are other conversations going on about that idiot and his videos.

A few technical comments from me and a few others soon saw him turning off comments - as he is prone to do when proven to be technically in error.


Simply, use the ignition sense function to control your DCDC device and have no problems at all.

And as mentioned, if the Aux is full the DcDc unit will soon stop feeding it and the other battery will charge up.

[scarry]

Or if you use the Traxide system,with the older SC80,put a switch in the SC80 earth wire and charge each battery separately.
Very easy to do.For some reason the batteries seem to charge better if separated.
Thats my experience anyway.

[Hugh Jars]

I have my BCDC switched via the ignition, so it doesn't fire up unless the car's running.