Solar battery maintainer?

My MG garage is not near electric service, and I don't want to have a long extension cord running out there 24/7.

I wondered if anyone has used a solar battery maintainer?

There are *many* on the market these days - but I'm wondering if they have the "oomph" to keep a fully charged car battery fully charged, as well as the proper circuitry to check the voltage and not overcharge the battery. South facing exterior wall, not shaded, six to eight hours sun a day.

Thanks.
Tom M.

One panel could easily do it. Think of the panel as putting out 1 or 2 amps of 12 Volts. Here are some choices from Northern Tool.
https://www.northerntool.com/shop/tools/product_200660262_200660262

I used one like this in my old tent trailer to keep the battery up.

Jerry

Harbour freight has them starting at $13.99

Thanks gents. They're certainly affordable, but I'd feel better hearing from someone who can tell me the unit they're actually using, and how it's working for them.

I had a solar car battery charger unit about ten years ago - failed after two days. Replacement was DOA. Third (same model) would output only about 1/10th of the advertised output on a bright sunny day.

Tom M.

I have about 30 watts of solar power on my boat. It provides all the electrical power I need but my needs are very simple. I do not have a "battery maintainer" but I have repaired several of them for friends. The only failures I've seen are in the connections to the power cord. A bit of solder and they are going again. I've not paid attention to brands but I don't see and substantial differences.
I do not use one with my cars. If stored for more that a few weeks, I disconnect the battery. I'm gone for 5 or 6 months in the winter and most of the cars have enough voltage to stat when I return in the Spring but I usually charge them first.
The lack of power for a charger at your shop might make the maintainer worthwhile. I don't think you need to worry about oomph either, most are 1.5 to 2 watts which is more than adequate unless you have an electrical draw on the system. I'd disconnect it anyway.
As for output, that's a bit tricky to measure. If you have it connected to the battery, the output will vary according to the state of the battery. You'll need to disconnect the battery and measure with no load and of course use Ohm's formula to compute watts. The latest chargers are quite reliable, in my opinion.
Hope this is of some help.
Tom

Tom - thanks very much for the detailed comments.

I learned the hard way not to just disconnect a battery for the winter - battery went dead as a doornail. Removing the battery from an MGTD isn't the easiest thing in the world, so I'm compromising between no extension cord, and not moving the battery.

Here's what I decided on:

https://www.amazon.com/gp/product/B00B7GC50Y/

It's 2.5 watt, 12 volt. I'll connect via the accessory plug on the fascia, which is always hot. Positive ground.

View attachment 49518

HMM. Positive ground. I hadn't considered that. There is a polarity sensitive diode in the charger that prevents discharge at night. This is over my pay grade but I guess if you hook it up pos to pos and neg to neg you will be OK. Still might be wise to disconnect the ground on the car. Maybe one of our better informed members will chime in.
Tom

I'm no electrical engineer for sure. I've been using my regular battery maintainer via 120v extension cord, pos to pos, neg to neg, and it's working fine, charging right up and shutting off when charged. Seems the same hookup should work with the solar charger.

Interesting point however. Basil has an EE degree, so maybe he'll share the wisdom on this.

Edit: unless I'm completely overlooking something obvious ... On these simple cars of the 1950s-60s, the charger is charging the battery, not the charging system. It's connected directly to the battery terminals (or to wires connected to the terminals, like my unswitched accessory socket) - so I don't see a problem going pos to pos, and neg to neg.

(If I'm wrong, I figure I'll be covered in spattered molten lead soon ...)

T.

TomMull said:

HMM. Positive ground. I hadn't considered that. There is a polarity sensitive diode in the charger that prevents discharge at night. This is over my pay grade but I guess if you hook it up pos to pos and neg to neg you will be OK. Still might be wise to disconnect the ground on the car. Maybe one of our better informed members will chime in.
Tom

Click to expand...

Yes, just hook it up as you suggest, and it should be fine. Positive or negative ground should not matter. It's only an issue when you have a piece of equipment that is negative ground and your car is positive (or vice-versa). For something that does not have a chassis that must be grounded to the car, that's not an issue.

Check with your local RV dealer, they use them on the RVs to do their batteries while in storage.