BadDog

I upgraded my alternator to a 135 amp single wire due to the current draw of stereo, fuel pumps, exhaust solenoids, refrigerator etc. The alternator seems to be working but it still takes a long damm time to charge up a battery when it is close to dead. I am using 2, 225 minute batteries on a one two all switch. I have a ammeter that you lay parallel to the alternator output wire that reads the amps the alternator is putting out.

At 1800 rpm charging against one deep cycle battery that was drawn down to 11.75 volts it only shows putting out 20 amps. The voltage measured on the battery at 1800 rpm is 13.2. To verify that the ammeter is working correctly I left the lights on in the van for 10 minutes and battery voltage was 11.95. Started the van up and the ammeter jumped to 50 right off the bat at an idle. It would seem that my alternator is not putting out much current. I checked the output on battery 2 (it was fully charged) and it showed 8 amps, that is about what the normal draw of the fuel pump, clocks, Crane box etc, would be when running.

I know that the closer to fully charged that the alternator is the less output it will show but at 11.75 it should put out more than 20 amps? Can an alternator gradually fail or is there something wrong with the internal voltage regulator, it was showing 13.2 while charging. Does the alternator have problems with deep cycle batteries? Both batteries load check fine.

Tim T.

baja2700

Alternators were never designed to recharge dead batteries. when a battery is discharged it has a very small internal reistance. This generally causes the alternator to show a high charging voltage. When you upgraded your alternator did you upgrade the output wire? If you did not this could cause the wire to heat up, which increases resistance and slows does current flow.When batteries are discharged your best bet is to recharge them with a battery charger.Once you recharge both batteries, wait one hour then check them with a digital volt meter.Check one battery at a time and look at the resting voltage. Then check each battery with the engine running at idle and at 2000 rpms. resting voltage should be about 12.6 at idle about 13.2 at 2000 rpm about 13.8-14.0. Low reading can be caused by a bad regulator worn brushes,loose connections, internal shorts a loose or worn belt.

BadDog

The alternator output is directly to the ALL post on the battery switch with 4 gauge wire. Belt is new and tight. With a fully charge battery I am only seeing about 13.3 at 2000 rpm. I don't really run them down to dead but they do get low. It just seems strange that a crappy little Ford Freestar (yes it is a dam mini van but free from the company) will take a slightly discharge battery and throw 50 amps at it. In a matter of minutes the van battery was all the way back up and the ammeter showed like 5 amps.

It seems to me that a battery that is run down to 11.75 should really cause that alternator to send at least 50 amps to it. That is why I bought the big alternator. It is rated at 135 amps.

Tim T.

BadDog

TTT

Surely someone knows more about alternators than I do...

deboatmon

I totally concur with baja2700. Alternators are definitely not designed to charge "dead" batteries. If you are draining your batteries that much, you need more batteries. I too have 135 amp alternators and I am running six (6) deep cycle 210 amp hr Interstate batteries. Yes it's lot's of extra weight but it's definitely worth it. For extra heavy duty applications, the wiring between everything should be professionally made custom crimped heavy duty marine grade wire and all terminals should be regularly checked.

Running your batteries down as low as you are will lead to more trouble. Add more power.

As far as charging rate, check your regulator.

baja2700

I think at this point I would remove the alt and have it checked. While its out charge up the batteries and have them load tested. If the batteries are OK then the regulator has probably gone south. Now I'll get on my soap box...
The biggest problems we have with electrical systems is they were not designed to keep up with the load that we place on them. Many audio systems can draw 200+ amps and even though we have placed larger alternators in the system they cannot keep up with the demand. My advice (yes I am an engineer and design audio and video systems) is to buy woofers that are at least 90db effecient. If you have 2 woofers and one is 90db effecient and the other is 87db effecient it will take twice as many watts to run at the same volume with the 87db woofer. Or you can run the 90db woofer with half as much power as the 87db woofer and still have the same volume. When running woofers use class "D" amp. This type of architecture is 90% effecient and therfore makes more power and generates less heat. Use the standard class a/b design to run your mids and highs. The class a/b only is about 60% effecient but it does not take that much power to run mids and highs