charging problem

[hamondale]

This post is generic to all engines, but I didn't know where to park it. It is maintenance related (or lack thereof).
I have a 3.4 crate motor in a small hot rod. I just dicked around for three days on and off trying to diagnose a charging problem. On Tuesday I first noticed that I had no amps and low (~12) volts instead of the usual 30 amps and 13.8 volts. Once in a while when I was checking and testing, all of a sudden I'd get charging volts/amps. Then it would quit charging again.
After thrashing through all sorts of wiring checks and trying a new alternator, tonight I was leaning toward thinking the battery (Die Hard Gold) was bad, although it cranks great, and a battery charger will juice it. Then I realized (duh) that in the five years I've had this car on the road, I had never added any water to it. (It's in the trunk - hard to get to and easy to forget about.)
Each cell took about 4 oz. of water, and as soon as I started it up, it was charging again. Don't know if it will last, but it looks like progress.

Question - does it make sense that not having enough electrolyte in the battery would cause a charging problem like this, and topping it off has brought it back? I stink at electrical problem solving and I'd appreciate any insight.
Thanks

[grassulo]

yes, a battery with low water is a capacitor with the air between the plates as its dielectric, soaks up charging current like a sponge and turns it into heat, like when a radio transmitter operator uses a dummy load so they wont broadcast their test signal. It should be fine now, but replace the battery anway if it's still under its warranty.

-Garret

[hamondale]

Thanks Garret, good explanation. System is charging, but still just a bit different. After I put the water in and it seemed to work, I put the battery on the charger. After charging overnight, the charger levelled off at about 1 amp. Usual full charge is about 2 amps. Might that suggest that the internal resistance of the battery has dropped, i.e. something is a little cooked?
Also, now when I start up, it doesn't show any charge, and then when I idle up to about 1600RPM, it kicks in and is fine. 20 - 30 amps, 14 volts. I haven't dug up the warrenty on the battery yet, but is it likely to be bad or damaged? Cranks the starter with no problem at all.
Thanks much -

[grassulo]

being that the battery is old and abused, I would replace it, plates could have corroded from sitting with low water. About that odd charge condition, you mean the dashboard ammeter (you said 30 amps so I'm going to assume its an ammeter) shows 0 amps of current and then jumps back to 20~30 when you rev the car for a bit? What kind of chassis/body is this hot rod built on, and are you using the old stock wiring harness? This is starting to sound like a case of ancient wiring if its an over 40 year old car, we'll need to dig out the handheld volt/ohm meter and start looking. One, test the current and voltage coming off the alternator's charging wire when you start it up, don't rev it, ground the negative terminal of your handheld volt/ohm meter (if you dont have one of these, go out to radio shack and buy a digital one, youll need it again trust me!) and the positive on the charging wire of the alternator, if current off it shows up fine then pull the volt and amp gauges and check them with the volt meter, if its intermittent and the alternator isn't the culprit, you may have a loose connection to the gauges themselves.

-Garret

p.s. It may be a good idea to pull the ammeter out of the dash anyway and check its connectors. Ammeters draw a LOT more current than voltmeters, and thus aren't used much on modern cars because of that. check where the old ammeter meets the new motor's harness and look for cooked plugs or burned wiring and upgrade with heavier gauge wire as needed.

[hamondale]

Thanks, Garrett, the car is an Austin Healey Sprite - see http://tinyurl.com/5a92d
All of the wiring is new. Painless Wiring fuses/circuit breaker. The ammeter is only two years old, since the original one did fail, and go to high resistance.
I have been through most if not all of the tests that you describe. I even bought the Radio Shack digital multimeter. Nice tool.
The whole charging circuit from the alternator to the battery post has been checked section by section. I did disconnect and bypass the ammeter. I have also checked my ground connections. I even made up a temporary wire and grounded the alternator casing directly to the battery post.
After adding the water, now the charging shows on the ammeter and voltmeter when I rev to ~1600 RPM. If I start it up just at idle, I get no charge. Rev to 1600, it kicks on and stays on, even when it idles back down.
I can tolerate this short term, as long as there's no chance I'll get stranded somewhere, but I will probably go ahead and replace the battery in the next week or so. Thanks for the info.

[grassulo]

take your alternator apart and test all its diodes, since i noticed you have the older style GM alternator, which can be disassembled, it sounds like the regulator is not supplying current untill the feild coil strength triggers it, this sounds to me like possibly a bad transistor or diode in the alternator, it should charge at idle right from the start. If the car has a seperate voltage regulator, or rectifier, replace it, Ive seen old honda and triumph motorcycles do the same thing, and their regulators or rectifiers were going, I would replace both, or if their contained in the alternator, see about disassembly of it and testing.

-Garret

[hamondale]

Thanks, Garret, I will have a look at the alternator and see if anything's up. Probably will replace the batttery as well.

[Juglenaut]

Idle RPM power of the alt is important, if it to high for idle then that might explain that. Is this car load managed?? If so, the alt start charging if the battery falls below a certain level.

The regulator is a voltage device not a current follower. Most ammeters made today use a comparator set-up that uses very little current.

Have you tried load testing each cell??? Well if your full charge amp rate is 1 amp now ove 2 amps before this can mean that the electrolyte is still active in the battery, the acid has turned over to salt, or there is just more surface area for lead ions to atract to.

Load testing entire battery to find internal impedance. Find 2-500ohm resistors as closly matched as possible and as close to 1kohm total, now the point of this is to create a light load situation becasue you are tring to measure impedance. Hook the up in series to the poles to create a voltage divider (current should be no more that 12mA), take measurements unloaded and not installed in the car though all this, then load up the battery, measure voltage at the poles, move the ground clip to the divided bank and measure voltage drops over both resistors.

Measurement to get. You can load test the battery at 30amps with a 500watt .5 ohm resistor (expensive) to get heavy load delta.
Unloaded source Voltage
Loaded source Voltage
With to top to you can get Delta change in percentage.
Measured positive resistor V drop, and Negative resistor V drop add these together subract from loaded this will give you Voltage drop over the battery (ex. 5.7+5.6=11.3{12-11.3=0.7} 12mA current>0.7VDC/12mA=58.3ohms
Delta % unloaded divided by loaded subtract 1.0 times loaded resistance this should give a number close to above.

Now if load testing at .5 ohm expect a huge difference if delta, I'd say around 15% and impedance will drop according the the load being applied if it doesn't then that is bad.

[hamondale]

This is a small hot rod with a basic Painless Wiring setup. The ammeter is in the main line and is carrying whatever the alt puts out.
Your advice sounds good, makes sense, but I have to say - the battery is in the trunk, and in this car, you get into the trunk from behind the seats. I have to be a contortionist to get there. To see what I mean, see

http://tinyurl.com/5a92d

If I'm going back in there again, it's going to be to replace the battery. Plus I work a job where I'm paid by the hour, so I'd be better off working the extra time and just buying a new battery.
What I want to know is, if the charging comes on and stays on once the RPM have been up to 1600, is it ok to drive for now. This isn't a daily driver, and if I can just get through until around October or so, I'll change the battery in the off-season.
Thanks very much for the explanation and advice.