How do I test charging with only a Multimeter?

[Hud3]

Originally Posted by Vasco

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.

Ditto what Vasco said, Mark. He's absolutely right. The 12.3V reading after 45 minutes indicates to me that your batteries are closer to a 50% charge state.

[s/v Thea]

Mark,

I'm assuming that the 12.52 measurement was after shutting off the engine? If it was while charging after an hour with a 80 amp alternator into 110 AH batteries you have a problem with your charging system, if on the other hand the voltage is approaching 14V while charging then you could be alright.

I would monitor the voltage in the batteries using your meter and when they drop to 11.8 volts or so run the engine for an hour. Assuming a more or less constant load if the interval between charging cycles does not get shorter then your charging system in operating properly.

Doug

[Therapy]

Originally Posted by Vasco

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.

I strongly concur with this.

I think you are slowly killing your batteries.

You are on a budget I know, and going a long way........good luck.

And after thought of "no way she would be buying a dress" before the charging system (and the other boat systems) is up to snuff is a small part of why I am sitting at my desk and you are not!!

Fair Winds!!!!!!!!!!!!!!!1

[ssullivan]

Yeah... I'm sorry Mark. I was trying to back off from forcefully tell you to get the electrical system in order before relying on that autohelm for this trip... didn't seem you wanted to hear it.

BUT... I would feel bad if I didn't say it again: The 110AH will not likely work with your setup day in and day out. I agree with the others.

[hellosailor]

Mark-
What you want to do CAN be done.

Will it be lab grade precision? No. But it can be done and can give you reliable results if you bear a few things in mind.

First, a $20 or even $80 multimeter usually has a PRECISION of four digits, but an ACCURACY of only 2+. The rated accuracy on the DC voltage scales may be 1/2%, which on 12.00 volts mean it may be off by 00.12 volts. And, there is usually a "float" of 2 or 3 "LSD" least significant digits, so 12.00 may mean 12.03 or 11.97. Add in your 1/2% error, and 12.00 volts could be 12.45 or 11.85 volts on the display. You don't and won't know that for sure, although most cheap meters tend to display plus-or-minus 0.20V within reality.

Back to the practical side: Put the meter in 20VDC mode, stick the test probes on the battery. If the battery has been sitting isolated and out of circuit for 24 hours, the readings will be valid. If the battery has been given a charge, the readings will be INVALID, because of something called a "surface charge". This is, literally, the effect of the electrolyte acid not evenly transferring a charge in the battery, and it means that your battery will read deceptively HIGH after a charge.

To compensate for this, you put a reasonable load (like all the running lights and cabin lights) on the battery for 2-5 minutes. then shut it, and test the voltage. That short drain pulls off the surface charge from the plates, and the voltage you read now is pretty much valid. (And accurate, if the meter is.<G>)

Depending on what they are made from, lead acid batteries measure roughly 12.7 volts when fully charged and brand new, dropping about 1/10th of a voltt to 11.6 or 11.7 volts when they no longer hold a useful charge. You might get one engine start out of a lower battery--but you won't be able to run lights, etc. for more than a few minutes from it. Call it discharged and dead.

Now, when you fire up the alternator, that should put out about 14.4 volts, and you should see 14.4 volts at the battery. 13.8 volts from an older cheaper regulator, or if the batteries are fully charged and the system is just loafing. Shut the alternator, and you'll read 13.6 volts at the battery--that's the surface charge, and you can watch it go away over the next few hours.

If the alternator voltage is over 14.4 volts, you have a bad regulator. They can hit 16-17V and at that point, things start to burn out.

All of the above is 'good enough' most of the time. If you really want to measure amps and see what the battery is doing, you can use a SHUNT, which is just a very low caefully calibrated resistance wire, in line with the batteries. For instance, you can buy a 100A shunt (it will look like a metal bar with screw terminals at each end) and install it in series with a battery cable. Then, you take your cheap multimeter and put it on the 2000 MILLIVOLT scale, and connect it to each side of the shunt. You are now reading the voltage DROP in the resistance wire (the shunt) which increases as the amperage through the wire increases. If you use a foot a 4AWG cable as a shunt (or, tap into a 4AWG battery cable at two spots exactly 1 foot apart) you might measure a one millivolt (0.001 volt) drop per amp of current drawn. So your cheap multimeter, punched into a 4AWG battery cable, could measure 2000millivolts, or a two thousand amp draw. (Don't worry, the cable would be on fire by then.)

Whatever battery cables you have--you can look up their resistance online in charts, and use them as shunts the same way. Again, this is not LAB ACCURACY, but it gives you a relatively good guideline. I'd stick to the voltmeter, by the way, and not punch holes in the battery cables as a matter of course.

If your batteries read "12.5" when fully charged and allowed to set for a few hours this week, and "12.3" next week...you know you've lost 20% of the battery capacity or drawn a bigger load or just not recharged them as much, along the way. And that's the primary value of using a multimeter, you CAN reliably get an indication of those 10% CHANGES in battery state. The meter may not be accurate--but it will usually show THE SAME numbers each time, giving you something repeatable to base decisions on.

If you want a quick check on the meter's numbers, buy a fresh silver-oxide watch or calculator battery, a physically big one. They have a shelf life of years, so the voltage they display on your meter should be unchanged from one month to the next. Is that lab-grade meter calibration? Hell no, but again, it gives you a reasonably good way to tell if your meter is staying constant (in its display) from one day to the next.


How's that for a not-too-technical nuts and bolts way to get you started?<G>

[bill good]

Mark,
It sounds like you need to have the alternator checked. 6 dresses $1.50. I bet $2.00 should cover an alternator check!!. Any auto electrician will be able to "bench test" the alternator after you check for faulty wiring. The panel lights are the same as the voltmeter but are only able to show if something has changed & need your attention while other instructments will give trends & indicate more about your systems. You could disconnect the positive lead to the panel & test the top light is reading by putting a 1.5v torch battery in series to lift the voltage to test if the panel is OK. (if you do'nt under electrickly do'nt try) I would start with the alternator check!!

Regards Bill Goodward

[Ex-Calif]

We have the 3-idiot light gage that we bought in West Marine - It plugs into a cigarette lighter. I am not sure where you are now but you could get one at an auto store, I bet.

When our sustem is working properly the bottom and middle lights are illuminated once we start discharging. Anytime the engine is running the 3rd light is on. If we motor more than an hour the thrird light stays on a day or two.

Our alternator died and our 2 house batteries ran the boat for about 2 weeks. We draw zip for current usually. The bottom and middle lights were on until finally the middle light went out and we did not have enough juice to crank. When you are down to one light it's game over.

Another idea is that while you are at the auto store, buy an aftermarket ammeter. rad how to install it and plug it into teh system temporarily.

With 3 idiot lights and an auto ammeter you should be able to tell what's going on.

[Joli]

Yep, we bulk charge at 14.2 V then absorb around 13.2 V.

It sounds like you are slowly killing the batteries Mark. What regulator do you have? Gotta look into this or as Vasco said you will be hand steering a bit, actually a good bit. You may be getting close to the point where the batteries do not have enough oomph to excite the field so you can not charge.

Joli

Originally Posted by Vasco

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.

[Tom Spohn]

Have you checked the specific gravity of the battery? How long have the batteries been aboard?

[MarkJ]

Thanks for the advice everyone I'm working on it


Mark

[Lancerbye]

I would have to ditto Hellosailor's procedure. It doesn't sound like your charger is putting out enough. Make sure your fan belt is tight.

[hellosailor]

The fan belt is a good point. If you have the conventional "V" belt, it is getting damned difficult to replace those from automotive sources as new cars have mainly gone to ribbed belts (less slippage, better transfer) in the past 20 years. V-belts easily slip and glaze, and the tension must be set manually. Too little and they slip, too much and they burn out alternator and water pump bearings. There's a simple tension gauge that can be used to make sure they are set right (if you don't have a calibrated thumb to measure deflection<G>) but those are getting hard to find too!

Any glossy appearance on the V-belt, or rubber dust under it, indicates a problem. And "belt dressing" should neer be used. It hides problems, doesn't fix them. Belts are consumables, after five years even the best are due for replacement with a good brand name. (Gates, Goodyear, Firestone, etc.)

[camaraderie]

Just a quick note on removing surface charge...you need a much larger load or a significantly longer time to remove the charge. Initial removal should be at 25% of rated CCA amperage (not 20 hour amps)...which in this case should be on the order of 50amps. Alternatively...you can use a lower amp draw for a few minutes instead of a few seconds.

[S/V The Goonies]

Originally Posted by Vasco

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.

Hi Mark, Can you give me an example of a 3 stage external regulator. I want to make sure I do it right when I build my charging system.

[Therapy]

In-Charge 3-Stage Alternator Regulator - Buy at Wholesale Prices from Online Marine