Using and understanding Multimeter

[BillN]

I am doing a lot of checking and testing to build my understanding of how my small solar system is working and I am a little lost on a couple of things.

Last night I ran my 12volt battery bank down to 12.5volts (80cpercent discharge). This morning before much sun was coming over the mountains I tested my battery bank and output from my solar panels, results follow:

Out put from the solar panels while disconnected from the batteries was:

21.05v
.22mA

Output from the Controller while connected to the batteries was:

12.39v
.12ma

Battery bank was:

13.02 volts

I am confused

[Steve]

Out put from the solar panels while disconnected from the batteries was:
21.05v
.22mA

Something is wrong with the amperage in your quote.

Either:
1. You are reading your meter wrong
2. You are reading panel output at night in the moonlight
3. Your panels are broken

I suspect the decimal point in your figure is wrong. Your measurement was probably 2.2a.

I'm not sure about the charge controller questions, others here are far more educated in this than I am.

Measure volts across the batteries and panels if you wish. You can read amps across the panels (Shorted) as long as they are not connected to the charge controller or batteries. Never read amps across the batteries or at the charge controller. If you do you'll get quite a bang and blow out your VOM and possibly your charge controller.

Your formula is correct, volts x amps = watts.

18v x 2.2a = 39.6w

[BillN]

Thanks Steve, I appreciate your reply.

Where you say (Shorted) are you referring to disconnecting the panels from the controller and simply test the amperage by placing the meters black lead to panels neg(black) and the meters red lead to the panels Pos(red)???

My meter has 3 settings for measuring DC amperage and I am not sure which one I should use, the book I have is of no help.

Three setting are as follows:

A = Amp

[Sunking]

[QUOTE=BillN;14440]

I am confused

[BillN]

Thanks Sunking!

Excellent information on the charging algorithms, I have a much better understanding and confidence in what I have been reading.

I have been taking amp readings from the solar panel while they are disconnected from the batteries but I am not sure of the correct setting on my meter.

My meter has 3 settings for measuring DC amperage and I am not sure which one I should use, the book I have is of no help.

Three setting are as follows:

1)A = Amp

[RifRaf]

sir you are reading mere microamps on the uA scale. My bet is that you have burnt out the fuses in your multimeter, open it and see, hopefully the meter has fuse protection.

You should measure current in series, never across the positive and negative like you test voltage, (apart from testing the short circuit current of a cell, in which case you do not want any other load). Never put your meter on the mA or uA settings for testing a decent size solar cell, you must only use the A setting and normally for a maximum of 10 seconds. a standard multimeter is not really the thing to be testing such high currents with.

[dubyoo]

Hmm... I had unusual readings like Bill and after the suggestion I checked my multimeter fuse - there's nothing there; no wire, no scorch mark, nothing! That's not right, is it?
Also I'm wondering how to check the current if it should be in series but not connected to battery or controller.
Can I just connect multimeter to +ve & -ve terminals of panel like Steve suggested?

Sorry for the thread hijacking Bill

[RifRaf]

dubyoo, take the time to read this link and you will understand, includes simple current measurements, how to avoid killing your fuse, and how to check the fuse
http://www.faqs.org/docs/electric/Ex...0Ammeter usage the entire page is a good lesson on how various features of different meters work

[windstar]

dubyoo, take the time to read this link and you will understand, includes simple current measurements, how to avoid killing your fuse, and how to check the fuse
http://www.faqs.org/docs/electric/Ex...0Ammeter usage the entire page is a good lesson on how various features of different meters work

Thanks for the link. Nice info.

[BillN]

dubyoo, take the time to read this link and you will understand, includes simple current measurements, how to avoid killing your fuse, and how to check the fuse
http://www.faqs.org/docs/electric/Ex...0Ammeter usage the entire page is a good lesson on how various features of different meters work

RifRaf thanks for the link!

I read through the document and I now have a much better understanding, the information within the document was exactly what I was looking for.

Bill

[Steve]

I'm also new to solar panel stuff but as an antique radio restorer, I am a very experienced VOM (Meter) user.

Keeping my novice solar in mind - the more seasoned people here please correct me if I'm wrong.

1. You don't want or need to regularly check current from anything. Certainly not a daily or weekly thing. (That's using the Amps function on your meter.)

I use the Amperage function of my meter once a month, right at the solar panel with the battery disconnected so I can properly align my solar panel on a clear day at solar noon for maximum output. That's all.

If you use the amperage setting on your meter the wrong way on the wrong thing you can cause a dangerous short, a loud bang, bright flash, burnt wires and blown fuses or cause your lead acid batteries to explode.

Don't buy an el-cheap-o meter that can only read a few amps. I've seen some which only read 1 amp max! My panels put out about 6.5 amps so I use a meter with a maximum amperage reading capability of 10 amps.

Keep in mind when you are reading amperage, your meter leads are as if a dead short one to another. 10 amps is a very large amount of energy and can do a lot of damage or even kill under the "wrong" conditions.

If you must read amperage first set the meter to read the maximum amount. That's amps, not uA or mA. Most meters will require you to place the meter leads in a different socket or hole in the meter to read maximum amperage.

For example the meter I use can cycle through different ranges of amperage, and I set the dial to maximum. 10 amps.

Then my black (negative) test lead remains in the Common socket hole in the meter and the red (Positive) test lead goes in it's special socet hole labled 10A.

Then to be double-tripple sure I am not going to short the battery with my test leads, I disconnect the battery from everything. Once the battery is disconnected then I disconnect my solar panel leads and make my reading there.

I hope that will help someone.

Battery testing-

I've been using my solar power system for a few months now without a charge controller. Because of that I must monitor my state of charge (SOC) carefully every day and make sure I am not deficit charging (Chronic undercharging) or over charging.

I've been doing a pretty good job using the VOLTS function of my VOM, but as others have said you simply must let the battery rest for a few hours with no load and no charging taking place for any remotely accurate reading.

I've tried 3 different types of battery testing hydro meters purchased at auto parts stores and all fail to read anything. I won't shell out the $$$$ for the expensive professional ones (At least not yet) and my meter seems to suffice.

In a nutshell:

Making a "minor" mistake reading Amps can do a lot of expensive damage to a lot of things. It does not need to be done often.

Reading volts is a different matter. You would need to really do some major idiotic blunder reading volts for anything bad to happen.

Unless you mean to read volts and your meter is still set up to read amps.

Bang!

[Sunking]

I use the Amperage function of my meter once a month, right at the solar panel with the battery disconnected so I can properly align my solar panel on a clear day at solar noon for maximum output.

Steve how does that work? Solar panels are current sources, and the output current is directly proportional to the amount of sunlight falling on it. If anything you want the batteries discharged and loads turned on so the system is demanding maximum power from the panels. In this case maximum current. So at solar noon with the system demanding maximum power, then you can adjust the panels for maximum smoke (current)

If you use the amperage setting on your meter the wrong way on the wrong thing you can cause a dangerous short, a loud bang, bright flash, burnt wires and blown fuses or cause your lead acid batteries to explode.

Agree and is the reason I rarely ever answer such questions of how to use a volt meter. If you do not know exactly what you are doing and the consequences of a mistake, you have no business using a multimeter unless I am one of your beneficiary .

I've tried 3 different types of battery testing hydro meters purchased at auto parts stores and all fail to read anything. I won't shell out the $$$$ for the expensive professional ones (At least not yet) and my meter seems to suffice.

A lab quality hydrometer with built in thermometer run around $20. Less than your DVM.[/QUOTE]

[Steve]

Steve how does that work?

Hi Sunking.
Actually I am reading current directly off the panel(s). The panel is disconnected from anything else other than my meter which is set to read amps.

My meter is shorting out the panel and reading 6.5-6.8 amps. I'm able to tilt the panel a few degrees for maximum output. In my case the panels are about shoulder height so adjusting them is easy.

Hydrometer-

After trying a few of the useless cheapie auto parts store hydros, I looked online but couldn't find any which were obviously different than those I already tried. It seemed the only ones I could count on to be accurate were ones like this example:

prohibitively expensive hydrometer

Do you happen to have any links handy to an affordable one?

[Sunking]

Actually I am reading current directly off the panel(s). The panel is disconnected from anything else other than my meter which is set to read amps.

My meter is shorting out the panel and reading 6.5-6.8 amps. I'm able to tilt the panel a few degrees for maximum output. In my case the panels are about shoulder height so adjusting them is easy.

OK I understand now, that will work great.

[Sunking]

Do you happen to have any links handy to an affordable one?

Here are a few I like.
HB Instruments
Chase Labs
Central Tools