Hi again all!

I recently was given a small solar panel (about 5" X 12"), called a Battery saver *plus*. No number for the amp rating or anything else. I had to solder on the quick connect 12V jack, but then it works fine.

Now, for the questions. My VOM indicates around 22.5 V. I'd like to know the amps it puts out, but am not familiar with how to do this with the VOM. Do I just hook up the clips across a nail or something and set the VOM for DC amps?

Some of you may know the watts of this unit, but I'm just playing around, learning what I can about all things solar

I'd like to do some experiments to see how much of a float this thing will do on a 75 AMH battery, prior to ordering maybe a real panel or two to keep my batts topped off.

Any ideas for future play-time will be appreciated!!")

My Kyocera 130 Watt panels..

Open circuit without a load, my voltmeter meauses about 20-21 volts, for my 12 volt nominal rated panels.

Under load, under optimum conditions with direct full sunlight with cool panels, they are about 17 volts.

They are designed to be able to deliver about 14 volts minumum so that they can charge 12 volt batteries under the widest variety of conditions possible.

If you can find the model number and brand for that panel, try "Googling" it for a spec sheet.

I sounds like it is probably this unit.

The output of solar panels is proportionate to their surface area, and to a lesser extent, the materials they are made from. Assuming you have one of the units like above, the specs say 12" x 4" but I suspect that is the physical size including the frame. In any case, it is no more than one-third square foot, and probably less, of active area.

Your DC amp setting on you VOM should be fine. The specs say 125 milliamps peak. Your VOM will have a maximum current that it can read. This panel is small enough that the max won't be an issue. But the max rating definitely can be a problem. If you were to directly hook your meter to the plus and minus terminals of your battery - it would be quickly toasted.

Dan

Check the users manual for your multimeter. If you don't have the manual Google for the brand name and you'll probably find a manual online.

Use the highest range setting (Amps) available. Be sure the leads are plugged into the right jacks on the meter. Put the meter inline in the circuit. As mentioned before, be sure you don't touch both sides of a battery with the meter in the Amps mode. It must be in the circuit, in series with the solar panel on ONE leg, either positive or negative.

Mac

Ok, thanks Gambler. I used to know some of this stuff

I think my VOM is rated for 10 amps max, say for example.

IF I *knew* a device draws less than this, I should be able to measure any device this way?

And that's the purpose of a shunt for monitoring a batt bank?

Thanks!

quote:

device draws less

Not draws less -- provides less into a dead short.

If you measure a 12 volt battery it will dump a thousand amps or so into your meter, the fuse may blow fast enough to save it.

If you measure a solar panel that is smaller than your maximum amp rating you can use your VOM in Amp mode by connecting directly to the pos and neg terminals. Best to do it with the panel shaded and then remove the shade. That will give you your maximum amp rating from the panel. Don't leave it hooked up long, your meter will start to warm up fairly quickly at higher amp ratings.

You can't get to watts from there though because the panel won't produce maximum volts and maximum amps at the same time. Your panel has a rating curve somewhere that shows the power curve so you can figure out your amps at any specific voltage.

Hooking it to a slightly discharged battery like Mac suggested will get you close to the panel's actual ability to provide watts of power.

rvMikey, First, DO NOT PUT YOUR METER LEADS ACROSS THE PANEL OUTPUT IN THE AMPS MODE. You seem to have already measured the volts (unloaded). 22.5 seems typical, but DO NOT power any device directly from the output. For a panel of this small size, your maximum amps available will be less than 1/2 (one half) Amp. A panel this size (or any size) is used to CHARGE batteries only and not for any other purpose. As a practical matter, with such low amps output available, it's safe to say that you can hook it up to any large wet-cell or Gel-cell indefinitely without 'overcharging' your battery. BTW, this little panel will NOT charge a depleted battery. It may "maintain" a charge on a seldom used battery such as in storage or with limited use. If you want to recharge house batteries, and you do not use an inverter, you will need a minimum of a 50-100 Watt panel(s)(4 to 8 Amps in full sun). If you intend to use an inverter, the sky's the limit. When looking for panals, compare Watts rating. I hope this helps. Regards, Tom & Jan

This thread has been dead since Feb 19th so your advice might be a bit late but I have to ask why you don't think you can measure the output amps of a solar panel with an appropriately sized multimeter?

quote:

Originally posted by Stanley P. Miller:
This thread has been dead since Feb 19th so your advice might be a bit late but I have to ask why you don't think you can measure the output amps of a solar panel with an appropriately sized multimeter?

Yes, it has been dead, but still interesting to me

As I still research this forum for my solar education. Which brings me to some old stuff I read yesterday. I think it was Handy Bob that sorta of convinced me that an adjustable controller was the most important thing in a solar system. His reasoning was that most controllers won't charge a batt bank fully becasue it won't stay at a high enough voltage long enough to do so. I'm still trying to get my head around this.......

In any case, the charge controller he recommended was the C40 Xantrex. Not too expensive and adjustable to his recommended 14.8 V for the bulk charge I think.

He also said he likes to place the controller close to the batts to help prevent voltage loss. Will this thing mount outside? (never seen one)>

With panels getting so expensive, I think I need to get some soon!

Is Bob still posting here?

The C40's and C60's are good controllers if you do not want/need MPPT technology. Set the bulk at 14.8 if you have flooded cell batteries. Set the bulk at whatever your battery manuf. recommends if you have AGMs. They are inside mount. You can mount them close to your battery if you like. That is actually a good practice. Butthey can be mounted farther away as long as the cabling to the battery is heavy enough. I generally use #4 welding wire these days, unless it is really a short run with small amperage.

A solar charge controller with MPPT and a battery temp sensor is always maximizing the charge to best charge your batteries under always changing sun intensity variables from morning to night and/or hot and cold conditions of the panels and batteries.

quote:

Originally posted by rvMikey:
...I think it was Handy Bob that sorta of convinced me that an adjustable controller was the most important thing in a solar system. His reasoning was that most controllers won't charge a batt bank fully becasue it won't stay at a high enough voltage long enough to do so...

Is Bob still posting here?

Handy Bob does still post here, he drops by from time to time. Also, you can probably find his email address on his profile.

Handy Bob gives sound advice.

Two points:

1. Regardless of what method is used to charge batteries, they need to be HELD at the recommended voltage until the absorption or acceptance phase completes, indicated by the charge current dropping off as the voltage continues to remain at the correct level.

The mistake some people make is to assume their batteries are fully charged once they REACH the target voltage. They are not. They have only reached the end of the boost or bulk phase, and the acceptance phase has just begun.

2. The other point is that this voltage measurement needs to be checked at the battery, near the end of the acceptance phase after the current has dropped off. The reason to check voltage AT the battery with a Digital Volt Meter is that you may have voltage loss in the wire between the batteries and the controller/monitor inside the RV.

Some higher end controlers are mounted near the batteries, and only the monitor is inside the coach. These will give a more accurate measurement. But many of us have to set our voltage a little higher on the monitor/controller to get the batteries to see the correct charge voltage.

Mac

quote:

Originally posted by Stanley P. Miller:
This thread has been dead since Feb 19th so your advice might be a bit late but I have to ask why you don't think you can measure the output amps of a solar panel with an appropriately sized multimeter?

Stan, You may be adept at the method you advised, but most novice technicians may risk damaging their meter measuring what amounts to a short-circuit current across about 22 volts, which will produce a relatively high current, and possibly damage the panel too. I wonder what this information really reveals to us anyway considering we are only interested in the current flow through a battery when the panel is connected to it (real world). In this case, to satisfy our curiosity, we would (temporarily) connect an ammeter in SERIES between the panel and battery thus telling us the current at that moment (only). If the current flow is somewhat lower than the ammeter maximum, the meter can be left in circuit for a while and one should observe a decrease in current over time as the battery becomes "charged". This is merely a good "go/no go" test to let us know that the panel is producing a voltage higher than the battery terminal voltage, and the battery is accepting a charge. This is true for any combination of charging source and battery so long as there is no 'controller' in-line which may alter what we observe somewhat.
We should remember that the little panels ( < 15 watts) are "maintainers" and NOT really practical chargers. Another problem I have seen is when some folks add big inverters to a system that was adequate for 12 volt lighting, pump etc. without adding more panels and batteries. There's no free lunch. Regards, Tom

I had a C40 for a couple years and was happy with it. The problem came when I added more panels going from 200 watts to 400, the C40 started to make RF noise that wiped out the AM radio and under heavy sun and nearly full batteries it would interfere with other 12 volt stuff. It was so bad it messed up the truck radio when towing!

We could flip a switch and disconnect either bank of panels and drop back to 200 watts and the problem went away, or got so much less it wasn't noticeable.

Our dealer looked at it and couldn't figure out what was happening but he did have a sale on MPPT units and would take ours in trade. Problem solved and the MPPT did help charging in the Arizona winters, didn't do a lot in the Montana summers aside from the early morning though.

Well, I sure got the experts here. And thanks!

I'd like a little better explanation, though, if possible on why Bob didn't like the MMPT controllers?? (I know how they work)>

Maybe just a model # or something? I can really see that a controller that wouldn't hold the absoption charge (thanks Gambler), would be counter productive, but WHY and which ones do you think, Jack? (I've read all your stuff on your site, btw)>

So, I like the mmpt controllers, but I don't like the price of the high end ones. Are these the only ones that Bob thought suitable?

I'll be putting up 250 watts, max, so a model number from any of you would be helpful. Say $200 or less??