battery monitor

joe0508 wrote:
Would this be a good purchase?


Clicky

Yes this type of digital volt meter can give you accurate voltage measurements. However I would not leave it plugged in for a long time. Also where to plug it in at? If you plug it into the dash of a motorhome, it might read the engine battery, not the coach battery (but who knows how your model RV is wired).

You could install a 12 volt cigarette lighter socket in the back of the RV and make sure that it is wired to a coach battery fuse.

There is a chart at Trojan Battery.com that give a good estimate of the amp hours left in their batteries at a certain 'resting' battery voltage. Basically once you reach 12.2 volts, you would want to run the generator to recharge for at least 1 hour, perhaps 1 hour early in the morning and another hour later at night.

Your RV will use about 35 amp hours daily to run just the CO and propane leak detectors, and the refrigerator.

Most batteries are about 65 - 100 amp hours each. The 100 AH battery is about 65 pounds, while a group 24 battery is around 35 pounds and 65 AH rating.

Good luck, and have fun camping!

Fred.

Joe, "good purchase" for what? Buying random items judging only by their description - this isn't going to work. Too much junk out there. Or misleading advertising - can be a good item but not for what you need.

You've found a 10W solar "kit" with lengthy description of how it would power everything - bullchit.
Now you've found this "battery monitor" - this is a voltmeter, not any "monitor". Maybe you don't need a "monitor" - I don't. But I do have a voltmeter, and ammeter built-in in my solar charger, and a few other things.

What are you trying to assemble - a cheap portable solar for camping? Or something else?

A Voltmeter, is not a battery monitor.

reading 12.2 volts under a 5 amp load is much different than 12.2 volts rested, not having seen a load or charging source for several hours.

Ciggy plugs are horrible connectors. The ciggy receptacles are usually very underwired, and if there are other loads on this circuit, as there often are, then the voltage reading will be low.

If you want a Voltmeter, then voltage at the battery terminals itself will yield a more accurate reading than anywhere else.

As others have said, a voltmeter alone is not a battery monitoring system. IMHO, a voltmeter and ammeter would be the minimum. If you can find the space to have a monitoring panel, you can buy inexpensive meters on eBay and mount them in an easy to see location.

Here is my monitoring panel. There is a 12v voltmeter and ammeter and a 120vac volt/ammeter. You can find many other examples in older posts.

I think the voltmeter is the only easy, practical way to measure the state of charge. The thing to keep in mind is that the voltage reads too high for hours after any charging - solar, engine or generator. With solar charging you have to wake up early to get a good reading. Voltmeters are inexpensive - I bought some on eBay from China that were only about a dollar and had a calibration potentiometer so I could make it pretty accurate. Also got some of these handy ones that plug into a cigarette lighter. They were out an average of two tenths of a volt, which is quite a bit for battery charge indicating. I wrote the correction on each one and found them quite useful.

You can use a hygrometer (well under $10) but that involves opening the caps on the battery and drawing out some liquid. In my case I can't do that without taking the battery out of the compartment.

The battery monitor measures the amp hours drawn from a battery so you get a pretty good idea how many need to be put back to fully charge it. I use a cheap one from eBay and believe it is reasonably accurate for a couple of days after being reset when fully charged.

The item linked will work great to monitor battery voltage.
In most cases this will be all you need.