alternator reads 10.5 volts?

kmarccoco · #1 (**permalink**) 06-11-2005, 10:09 PM

i just replaced my battery thinking it was from sitting. i think my new one is loosing power. i hooked up a volt meter to positive post and it reads 10.5 volts. wierd thing, when i disconnect wire from positive post, and then check volts it reads 14.2 at 800 rpm. why does the volts weaken when the positive wire is connected? it also reads 10.5 volts at the battery posts. is it a bad alternator, or some ground problem???

strictlypersonl · #2 (**permalink**) 06-12-2005, 04:19 AM

That battery is currently very dead! A flat battery will naturally reduce the net system voltage when it's connected to the alternator but I suspect that your alternator is also bad.

I would first charge the battery fully so that it's not part of the equation. Once it's charged, check its voltage under load - turn the radiator fan and lights on. You should still see 12-12.5 volts. Less than that indicates a bad battery.

Next, check the voltage regulator. Make sure that the case is grounded through the black wire. Use this guide (page 8) to bypass the regulator.

I suspect that the alternator is cooked.

kmarccoco · #3 (**permalink**) 06-12-2005, 04:24 AM

the alternator has a bigger pulley too. there was black dust on the front of the alternator near the fins.... thanks for the info...if i put a new alternator on, will it rechargs battery. i just bought the battery last weekend. its a optima gel...

strictlypersonl · #4 (**permalink**) 06-12-2005, 05:46 AM

I would still try to charge the battery before I replaced the alternator. Otherwise, you'll have to jump the car from another source to get it started. I don't like the idea of putting the new alternator at full load immediately with a dead battery - just a superstition of mine though.

Ron61 · #5 (**permalink**) 06-12-2005, 05:48 AM

If the battery has no bad cell or cells and is not to far down, yes, a good alternator will recharge it but you may have to drive a while depending on how far down it is. If it sets a lot get one of the $39.95 Battery Tenders fromNAPA or any other parts store and connect them when it is setting. I have used them for many years and have never had a dead or low battery as they will kick on and keep it at peak charge and also just to move the electrolite from time to time.

Ron

chopper · #6 (**permalink**) 06-12-2005, 06:13 AM

Second what Mr. Widener said. Optima gel-cell batteries will not take well to a standard charger, even one of the low-amperage types. You need something like a Battery Tender to charge them without frying the battery. As he further points out, the Battery Tender also has a set of terminals which you can permanently mount to the battery terminals and then plug the charger into while the car sits. It will keep the battery at full charge during those periods when it just sits.

kmarccoco · #7 (**permalink**) 06-12-2005, 12:06 PM

right on , thanks for the info.. bettery tender it is... and alternator.

kmarccoco · #8 (**permalink**) 06-12-2005, 12:28 PM

when i checked the voltage at the regulator switch(mentioned above) it read 10 volts or so. is it supposed to read 11.5. could that be the problem? what fuse is the regulator fuse?

strictlypersonl · #9 (**permalink**) 06-12-2005, 03:51 PM

The voltage at the regulator will never read above the battery voltage (unless there's been some kind of divine intervention...).

The voltage regulator's power comes from the top fuse on the driver's side.