DMCH alternator

[Bitsyncmaster]

I installed a new DMCH alternater PN 110101.

When the engine is at idle with blower on #4, headlights on low beam and AC running the voltage is 14.2 volts but every 18 seconds there is a quick dip to 13.0 volts. It's like the alternator switches off every 18 seconds. I did not notice it with the accessorys turned off but the battery could be holding the voltage without the loads.

Is this normal for this alternator?

[DMC-81]

Hi Dave,

I have the same alternator that I just ran for the first time yesterday and today, as I just got my engine running again. As I was watching the instruments like a hawk, I noticed a similar dip in the voltage gauge. I had my heat on full speed (to help bleed the cooling system), the radio, and the high beam headlights. It was a momentary dip and I didn't notice the accessory performance suffer. I did not time the dip or the interval, but I will next time I run the car.

Also, I read that with this alternator, the battery light blinks on startup as it is doing some checks, and then goes out after the car starts. Is that your experience as well?

Dana

[refugeefromcalif]

Did DMCH stop selling the Motorola 140 A alternator? The part # that was posted specifies a 120 A alternator.
I ask because I had a Major charging issue start today.

George

[Bitsyncmaster]

Hi Dave,

I have the same alternator that I just ran for the first time yesterday and today, as I just got my engine running again. As I was watching the instruments like a hawk, I noticed a similar dip in the voltage gauge. I had my heat on full speed (to help bleed the cooling system), the radio, and the high beam headlights. It was a momentary dip and I didn't notice the accessory performance suffer. I did not time the dip or the interval, but I will next time I run the car.

Also, I read that with this alternator, the battery light blinks on startup as it is doing some checks, and then goes out after the car starts. Is that your experience as well?

Dana

Yes my battery light blinks with the key turned on and engine not running. I'm going to do some troubleshooting as I think of things to check. First thing I want to check is to feed the battery light wire with a bench supply and the light bulb just to verify that circuit is not glitching.

[DMCMW Dave]

Yes my battery light blinks with the key turned on and engine not running. I'm going to do some troubleshooting as I think of things to check. First thing I want to check is to feed the battery light wire with a bench supply and the light bulb just to verify that circuit is not glitching.

Normal operation for that unit.

[kings1527]

I installed a new DMCH alternater PN 110101.

When the engine is at idle with blower on #4, headlights on low beam and AC running the voltage is 14.2 volts but every 18 seconds there is a quick dip to 13.0 volts. It's like the alternator switches off every 18 seconds. I did not notice it with the accessorys turned off but the battery could be holding the voltage without the loads.

Is this normal for this alternator?

I have the same unit and it operates exactly the same way.

[mluder]

Me three...

The battery light blink is normal operation for this unit.
I also have dips in voltage when the AC is running full on. Hasn't been a problem for daily use. I think it's a function of us comparing this car to our more modern daily drivers. IN all honesty I'm not sure that the instruments on modern cars are not just idiot appeasers... In other words, they don't display accurate data but rather go to "normal" operating readings at start-up just to make us think everything is OK.

Cheers
Steven

[DMCMW Dave]

The most important thing you can do when installing this, or any, alternator is to clean the grounds. This includes taking the alternator mount off the engine and cleaning the sides that contact the alternator and the back that contacts the engine. New hardware is a good idea too.

[Bitsyncmaster]

Grounds would not cause this 18 second cycle.

Using a bench power supply for the “battery light” circuit makes no change to that 18 second voltage dip.

Measuring current through a shunt on the alternator output the current is 64 amps at idle speed 950 RPM, blower on #4, Lights on low beam and AC on normal. Every 18 seconds that current dips quickly (less than 50 ms.) to 48 amps. It then rises linearly back to 64 amps in 1.2 seconds.

Measuring voltage with the same loads I get 14.7 volts with a dip every 18 seconds to 13.4 volts. The dip is more of a sine wave also for 1.2 seconds since the battery is supplying some power when the alternator switches to lower current.

I wonder why that alternator voltage regulator is doing that every 18 seconds.

[David T]

Grounds would not cause this 18 second cycle.

Using a bench power supply for the “battery light” circuit makes no change to that 18 second voltage dip.

Measuring current through a shunt on the alternator output the current is 64 amps at idle speed 950 RPM, blower on #4, Lights on low beam and AC on normal. Every 18 seconds that current dips quickly (less than 50 ms.) to 48 amps. It then rises linearly back to 64 amps in 1.2 seconds.

Measuring voltage with the same loads I get 14.7 volts with a dip every 18 seconds to 13.4 volts. The dip is more of a sine wave also for 1.2 seconds since the battery is supplying some power when the alternator switches to lower current.

I wonder why that alternator voltage regulator is doing that every 18 seconds.

It is very hard for the alternator to put out a lot of amps when the motor is not going fast. No alternator can put out it's full rated output at idle. My guess is to prevent overloading (and overheating) the alternator, the voltage regulator cycles it like the duty cycle of the A/C so it can handle the power without overheating. A better test would be at or above 1200 RPM. The alternator is a little "undocumented" especially when it comes to the blinking.