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Old 17-06-2008, 08:19   #1
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How do I test charging with only a Multimeter?

Hi Folks

Please don't help me with links to tutorials or 'go search' comments. I have already done so

Caveat: This section is not my most favorite on CF

Problem: My battery voltage lights have stopped working. The batteries are still charging. This occurred for a day or 2 when I was negotiating buying the boat but it fixed itself. Now it hasn’t been working for a week or so.
Its what some idiots call idiot lights, I believe.




When its charging and nearly full charged the top yellow light is bright.
When discharged the bottom red light flashes.

As its not working, and is not getting replaced till I get a budget again, I decided to buy a multimeter to test the battery charging.
(Both house batteries and the engine battery are new - thanks vendor!)

I bought the multimeter yesterday and studied last night.
This morning the house batteries needed a charge - I hadn't charged yesterday at all.
Using the Multimeter on the DC Volts on the battery terminals I got 11.83 volts which means the batteries are pretty low.

Batteries 2 x 55 AH

I ran the engine for exactly 1 hour and both batteries are now 12.52 volts which is
quite high. (45 mins after charging batts were 12.30 without much stuff being on)

So I can guess the battery charging system is working and that my panel idiot lights are malfunctioning.

Questions:
1) Is my above summation sounding correct?

2) Can I connect the Multimeter direct to the battery and see if there is the correct amount of Amps going into the batteries when charging? Its an 80 amp alternator.

3) What should I / Could I do with my idiot lights to try and fix them (be simple as the only idiot here is me!)

4) Is there any other method I can use with a multimeter to feel safe that my electrics (OK autopilot) will keep going for 8,000 miles before it can be fixed properly?



Thanks for your help


Mark
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Old 17-06-2008, 08:25   #2
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Mark,

Are you sure you've only got 2x55 AH batteries? And I take it these are your house batteries?
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Old 17-06-2008, 08:37   #3
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Quote:
Originally Posted by Vasco View Post
Mark,

Are you sure you've only got 2x55 AH batteries? And I take it these are your house batteries?
Mark,

Do you have any other means of charging aside from your engine?

If not, 110AH is pretty low to power your autopilot on an 8000 mile trip (assuming you will be doing long stretches in the Pacific).

See... aside from the refrigeration and lights and nav instruments and such, your autohelm (if you use it on this trip) will be a huge consumer of power. If you have to run the diesel often to charge the batteries back up, you may not have enough diesel capacity to make a safe trip.

You (we on the board) will need to go through your electrical consumption in detail to know if the batteries will be appropriate for the autopilot on an 8000 mile sailing trip. (My hunch, unfortunately, is that they won't)
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Old 17-06-2008, 08:55   #4
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It is probably just a loose wire or a bad connection in the back of the panel. Easy enough to check.

All that stuff about battery capacity is different stuff.
I suspect you meant 550. If you only have 110............well............ummm..........I don't know what to say.
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Old 17-06-2008, 09:02   #5
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Quote:
Originally Posted by ssullivan View Post
Mark,

You (we on the board) will need to go through your electrical consumption in detail to know if the batteries will be appropriate for the autopilot on an 8000 mile sailing trip. (My hunch, unfortunately, is that they won't)
Its fine, I've tested it and trialed it over 11 days at sea. It works. No refrigeration, 300 litres of fuel, 3 refueling stops, consumption 8 litres per day (less actually) and I actually bloody sail not motor sail!

The only problem is only as specified


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Old 17-06-2008, 09:20   #6
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You cannot test the amperage being put into the batteries with a common multimeter. Most of them are only rated for 10 amps and these need to be placed in line on the positive side to read the amperage. If you get one of the fancy (read expensive) meters that can be clipped over a single wire it is possible to tell how many amps are being sent into your battery.

Have you tested the yellow light itself to see if it is working or not. If it is something as simple as a bulb well that can be an easy (meaning cheap) fix or jerry rig.
Edit: Are the other lights working? The picture shows the green light working?


Hopefully someone with more knowledge of electrical will chime in.
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Old 17-06-2008, 09:22   #7
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Quote:
Originally Posted by MarkJ;172982[FONT=Times New Roman
Questions:
1) Is my above summation sounding correct?

2) Can I connect the Multimeter direct to the battery and see if there is the correct amount of Amps going into the batteries when charging? Its an 80 amp alternator.

3) What should I / Could I do with my idiot lights to try and fix them (be simple as the only idiot here is me!)

4) Is there any other method I can use with a multimeter to feel safe that my electrics (OK autopilot) will keep going for 8,000 miles before it can be fixed properly?
[/font]

Ok,

1) Your summation does sound correct.

2) It sounds as if your alternator (80 Amp) is working properly and delivering a charge to the batteries. If your multimeter allows (read the instruction manual), you can measure current going into the batteries. Be aware the current will *not* be 80 amps, or even half that most of the time. It puts out 80 amps when the batteries are dead. When they are at half charge or so, it will put out much less current. As they approach a fully charged state, the alternator will put out only a few amps. This is why you will never be able to fully charge your batteries using your motor as a charging source, unless you are motoring all day. It could also be the root of your 13V light not lighting up. Your batteries are not getting above 13V, so maybe all you will ever see is 12V (unless you motor for a day straight). This is a possibility.

3) If it's in your plans, you can motor for a day straight and see if the 13V light comes on or not. Otherwise, maybe you can find a 13.5V DC source to hook up the the idiot light sensor and see if the top light lights. Failing those ideas, you can borrow a battery charger and get a dock for a night and see if you can get the batts up above 13V and see if the light comes on. My suspicion is that since you are below 13V (as measured by the multimeter), that 13V light isn't going to come on.

4) Honestly, you have to look at your autopilot's consumption per hour in amps and see if it will exceed 55amps per day. It's the only way to understand if your batteries and charging system are up to task for your planned trip using the autopilot. A multimeter will not help you understand this. Only looking at the manual/label for the autopilot and knowing the battery capacity can safely say if your autopilot will be up to the task.

After you see how much power the autopilot needs, you will then need to determine how many hours of engine running it will take to bring your batteries back up to 80-90% capacity after each time period you drain them.

This #4 question cannot be answered without doing this correctly.
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Old 17-06-2008, 09:32   #8
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Mark,

A multimeter will only tell you the voltage at the terminals before you start the engine, during charging, and after charging. Same as the idiot lights. Unfortunately it will not tell you a lot about the state of your batteries. You require an amp meter to see how much is going into the batteries. I assume you have the standard alternator without an external regulator. This is a very poor charging system which will not charge your batteries fully even running two hours a day. Your usage may not be much without a fridge but running lights, propane solenoid and occasional use of the instruments and vhf will probably give you a draw down of nearly 40 amps per 24 hours. This is close to half your capacity. Your problem is not really one of capacity but one of charging. Without cold beer you could get by on 110 AH but you will need a better charging system as the batteries will get more and more discharged as the days go on. By the way, how do you get along without cold beer?
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Old 17-06-2008, 09:34   #9
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Quote:
Originally Posted by Charlie View Post
Have you tested the yellow light itself to see if it is working or not.
Yes all the LED's are working as the yellow flashes momentarily when some things on the panel are turned on.

Quote:
Originally Posted by ssullivan View Post

2) If your multimeter allows (read the instruction manual), you can measure current going into the batteries.
As Charlies post the multimeter only does 10amps so I guess that is out

3) If it's in your plans, you can motor for a day straight and see if the 13V light comes on or not.

I did motor for a day coming through the Panama Canal and it did not come on.

4) Honestly, you have to look at your autopilot's consumption per hour in amps and see if it will exceed 55amps per day.
After you see how much power the autopilot needs, you will then need to determine how many hours of engine running it will take to bring your batteries back up to 80-90% capacity after each time period you drain them.

I did this with an 11 day non-stop sail from St Martin to the Panama Canal. It was only after that when sitting in Colon that this problem appear. An 11 day test is fine for a 60 day 'real' sail
Thanks for your help, guys I really appreciate it


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Old 17-06-2008, 09:35   #10
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Oh, and "duh...."... I nearly forgot. Have you checked the idiot lights with the engine revved up and the alternator spinning well? Does the top one come on at that time?

(saves the need to get a dock/charger or motor for a day straight as a test)


It should be above 13V with the engine on and revving up. If the top light doesn't come on during that time, then you may have to remove panel and see what's back there (unless you want to just use the multimeter)

Here is a rough guide to using a multimeter to determine a "very rough" state of charge:

http://www.arttec.net/Solar_Mower/4_...20Charging.pdf
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Old 17-06-2008, 09:37   #11
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. By the way, how do you get along without cold beer?
You want to see the Before and After photos of my beer gut!!!!!!!!!!!!!

Quote:
You require an amp meter to see how much is going into the batteries.
I thought thats what I friggin bought! The multi meter has an Amp thingy on it. Can't I just conect it to the battery terminals during charging?
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Old 17-06-2008, 09:40   #12
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Here is a rough guide to using a multimeter to determine a "very rough" state of charge:
Thanks, I'll read it later. We are off shopping. Read: Nicolle is buying dresses. But thats fine because she bought 6 dresses yesterday at US$1.49 each!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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Old 17-06-2008, 09:40   #13
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Ok, so it doesn't come on when motoring all day. This can only be 1 of 2 things:

Bad alternator (not likely since you are getting a charge)

or

Bad idiot lights (most likely)

I'd say just live without the top light then until you get home. Use your multimeter and print out the graphs I put in the link above. You can get a rough measurement and make your way home. There are enough other challenges you probably are working with at this time preparing for the trip. A quick check with that meter will let you know all is well, and you still have lower part of the idiot lights to let you know when all is *not* well.
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Old 17-06-2008, 09:44   #14
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Mark,

Your electrical system might seem ok after 11 days at sea but it is slowly (and later more rapidly) deteriorating. Without a hi-output alternator and a 3 stage external regulator it is nearly impossible to bring a battery bank up to snuff using the engine only. Your batteries should be up to nearly 14v when charging so the 12.52v after an hour's charging is not "quite high" as stated earlier. Unless you are going to hand steer a lot you really should re-think your energy system while you have the chance.
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Old 17-06-2008, 09:47   #15
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Mark,

Here's the amp meter you need for testing.
Amp Meter - More Categories - Compare Prices, Reviews and Buy at NexTag - Price - Review
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