Charging your battery? Want more power? Watch out for this...


Gotta get outta here...
Sep 20, 2003
So, I'm doing some tests with a solar system and my fridge. Temporary installation. Checking numbers and the like. What can I say, it's quarantine time...

I just noticed that the battery voltage given by my charge controller app and the voltage at my fridge were significantly different. Like 0.5V. That's a lot for a 12V system and more than the expected uncertainty. Not surprising that there'd be a difference normally cuz it's a long run of wire, but here the fridge was off, no current, so something was not right. I'm thinking "damn, one of those voltmeters is bad", unlikely as it is. So I go to the battery, and check the posts voltage. Same as fridge voltmeter. Good. Then I check the voltage at the controller vs the app value. Same. Good. So both voltage readings are fine. But shoot, that means there is a big drop between the controller and the battery. Yet, I put the controller next to the battery to limit voltage drops and have better temp compensation. Now I'm thinking the wires are too small. And sure enough, part of the way is my standard 10Ga but there is the end where I go from my beloved Anderson PP to the battery clamps and that is a smaller gauge. Maybe 16 or even 18Ga. Normally, I mark my cables but that one isn't, so I don't know exactly. I just grabbed it quickly off the rack. I am thinking the voltage drop should be small, though, cuz that bit is only like a foot long but it's running 6A so that's quite a lot for a skinny wire. So I look up the voltage drop but it should be only 0.1V for 16Ga. And sure enough I measure it at about that. That's not it. So it finally dawns on me. The spring CLAMPS! Sure enough, checking those directly, I see about 1/2V drop just over the clamps to posts connections. Likely cuz they are roundish and without thinking I put them on hex nuts cuz the lead posts are not usable as is. Evidently, the contact was poor which is not surprising in retrospect given the odd geometries. I should have known better. So I put in ring connectors and brought it down to 0.1V or so loss. Gotta clean those contacts a bit still apparently, but better.

Sooo, wanna charge your battery? Want an extra 1/2 Volt? Don't be like me. Watch those clamp connections. Easy to forget about those and just clamp them on haphazardly and waste some precious solar power... And more generally, watch out for those wire sizes and connections.

(Yes, it's obvious and you know better. For me, only too easy to forget, sadly...)

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