Strange Alternator behaviour

[neil1967]

I have just fitted a prestolite 90A alternator to my Perkins 4018, with a sterling alternator controller and smart charge splitter. When I start the engine from cold, which involves setting full throttle until the engine starts, then rapidly throttling back, the alternator behaves normally, displaying revs, the ignition light going out, and charge delivered to the battery. When the engine is warm however, I tend to start it by just turning the ignition key. Engine starts fine, but the ignition light remains on, no revs are displayed, and my smart charge splitter gives a 'low charge' indication - clearly the alternator is not charging - and it remains like this whilst under low power - say 1500-2000 rpm. However, if I rev the engine to perhaps 2500 rpm (just blipping the throttle, not sustained), all goes back to normal. Is this likely to be a problem with the alternator it self, or possibly the installation? I suspect the energising circuit is not not working properly, but I can't work out why blipping the throttle would cure the problem. Any thoughts?

Neil

 

[coopec]

Could the points on the voltage regulator be sticking? (I used to have a car that used to do that)

 

[Heckler]

Could the points on the voltage regulator be sticking? (I used to have a car that used to do that)

Alternators dont have a voltage regulator that you describe, dynamos used to!
The symptoms are classic ones of the brushes either being worn or sticking?
Stu

 

[coopec]

Alternators dont have a voltage regulator that you describe, dynamos used to!
The symptoms are classic ones of the brushes either being worn or sticking?
Stu

Stu
Sure, I missed "I have just fitted a prestolite 90A alternator to my Perkins 4018"

(I just assumed the 4-108 had the original dynamo.)

 

[sailor211]

With my system i often have this problem, it is to do with the with the split charge diode. A quick short between the connections with a steel screwdriver works.

I have a fix with a relay off the ignition switch and circuit taken from the sterling website i think. This had an explanation of the problem


Mine was a "professional " installation and the man admitted it happened with his installation on his van and he just shorted it!!

 

[VicS]

I have just fitted a prestolite 90A alternator to my Perkins 4018, with a sterling alternator controller and smart charge splitter. When I start the engine from cold, which involves setting full throttle until the engine starts, then rapidly throttling back, the alternator behaves normally, displaying revs, the ignition light going out, and charge delivered to the battery. When the engine is warm however, I tend to start it by just turning the ignition key. Engine starts fine, but the ignition light remains on, no revs are displayed, and my smart charge splitter gives a 'low charge' indication - clearly the alternator is not charging - and it remains like this whilst under low power - say 1500-2000 rpm. However, if I rev the engine to perhaps 2500 rpm (just blipping the throttle, not sustained), all goes back to normal. Is this likely to be a problem with the alternator it self, or possibly the installation? I suspect the energising circuit is not not working properly, but I can't work out why blipping the throttle would cure the problem. Any thoughts?

Neil

What you describe is not all that uncommon.
Insufficient initial excitation to get it generating.
Fitting a higher wattage bulb as the warning light might help but would need to study the details of the Sterling controller, the charge (diode?) splitter and the Prestolite alternator to be really sure of the best course of action.

Certainly nothing to do with sticking contacts.

Unlikely to be a problem with brushes either if this is a new alternator.

 

[coopec]

With my system i often have this problem, it is to do with the with the split charge diode. A quick short between the connections with a steel screwdriver works.

I thought I was the only one that did things like that!! When my voltage regulator played up on the VW I used to whack it with a piece of timber which I always had in the car just for such purpose.

 

[RobBrown]

Yep- I agree with Vic S's explanation. Got a replacement 75A Prestolite in my set up (plus Battery-Mate & Sterling Alternator Regulator) & and same symptoms- need about mid range revs to get the tacho to read, thereafter read out @ tick-over 950 revs as normal whilst engine is running. I live with it as normally start from cold on mid throttle anyway.

 

[RichardS]

On many of the boats I have chartered over the years I have had to blip the throttle up to 1.5k - 2k revs to start battery charging. If you don't do this the ammeter doesn't move off zero.

I always believed this was standard practice until I bought my own boat which does not require blipping, although, out of habit, I still sometimes do it "just to be sure"!

Richard

 

[catmandoo]

What you describe is not all that uncommon.
Insufficient initial excitation to get it generating.
Fitting a higher wattage bulb as the warning light might help but would need to study the details of the Sterling controller, the charge (diode?) splitter and the Prestolite alternator to be really sure of the best course of action.

Certainly nothing to do with sticking contacts.

Unlikely to be a problem with brushes either if this is a new alternator.

Vic

would it not be case that alternator is not going fast enough at low revs to produce high enough voltage to over come that downstream of ignition light . Should he not check pulley ratios or belt tension. If he switches off Sterling at I think it is the white wire as suggested option by Sterling then it would narrow problem down to alternator output at tick over .

cant see that higher wattage bulb would solve problem as with 12 volts upstream delta V across bulb would be bigger with same result alternator not got enough output voltage at low revs

 

[Alex_Blackwood]

+1 for Vic's reply. Perfectly normal for the alternator field to require a "Kick" to get exitation. I have even known it happen on big alternators (1.5-2Mw)
Beware of people bearing screwdrivers!

 

[boatmike]

+1 for Vic's reply. Perfectly normal for the alternator field to require a "Kick" to get exitation. I have even known it happen on big alternators (1.5-2Mw)
Beware of people bearing screwdrivers!

Agreed on both counts I have posted on here before regarding Prestolite alternators. I have had 2 on previous boats and have one on each of my TAMD41a engines on my current boat. All have been very reliable but need considerable RPM to energise when first started. This is NOT a fault and is common to all of them. Just get used to it. It's not a problem and only requires a momentary blip of the throttle. Once energised it will remain so even at a tickover.

 

[catmandoo]

Agreed on both counts I have posted on here before regarding Prestolite alternators. I have had 2 on previous boats and have one on each of my TAMD41a engines on my current boat. All have been very reliable but need considerable RPM to energise when first started. This is NOT a fault and is common to all of them. Just get used to it. It's not a problem and only requires a momentary blip of the throttle. Once energised it will remain so even at a tickover.

if its A 90 amp Prestolite 20150113 the max speed is 10000 rpm, full rated out put speed is 6000 so with max engine speed 2300 this give pulley ratio 2.6:1 say 2.5:1 for a 6 inch engine pulley and with cut in speed quoted at which a voltage will be generated is 1100 rpm engine should be running over 440 rpm .Not sure what your pulley ratio is or whether you were upgrading . Pulley dia supplied with my 90 amp alternator is 2.5 inches which then would require engine pulley at 6 inches . All now depends on belt size . In my case belt was too small for load so I changed to an 80 amp alternator

 

[Heckler]

Stu
Sure, I missed "I have just fitted a prestolite 90A alternator to my Perkins 4018"

(I just assumed the 4-108 had the original dynamo.)

Being a smartie pants now, the 4-108 engines in the lincoln welding sets that I messed with in the late 70s had alternators fitted and I have suddenly remembered, they had a crude "ignition" set up that used the oil pressure switch to do something? Is that the same system on the OPs setup?
Stu

 

[pampas]

Being a smartie pants now, the 4-108 engines in the lincoln welding sets that I messed with in the late 70s had alternators fitted and I have suddenly remembered, they had a crude "ignition" set up that used the oil pressure switch to do something? Is that the same system on the OPs setup?

Stu

Oil switch interrupted the w/l circuit to allow the engine to run up without the alt. firing, thus reducing start-up loads. quite a common practice especially with single cylinder engines.

 

[neil1967]

Many thanks for all the input - i am reassured that nothing is fundamentally wrong. I will look at the pulley sizes/ratios to check they are appropriate, but by sight the replacement alternator looked to have a similar size pulley to the one I removed.

Thanks again

Neil

 

[boatmike]

Many thanks for all the input - i am reassured that nothing is fundamentally wrong. I will look at the pulley sizes/ratios to check they are appropriate, but by sight the replacement alternator looked to have a similar size pulley to the one I removed.

Thanks again

Neil

Actually Neil it needs to be exactly the same diameter for the rev counter to give you a correct reading. Very often the Prestolite is supplied with an undersized pulley. As I said before I have replaced 4 old alternators with Prestolites and in every case I have swapped the pulleys over and used the one off the old alt. to get the same revs.

 

[VicS]

good point about the pulley sizes and tacho calibration although I'd expect some adjustment to be possible.

 

[coopec]

Being a smartie pants now, the 4-108 engines in the lincoln welding sets that I messed with in the late 70s had alternators fitted and I have suddenly remembered, they had a crude "ignition" set up that used the oil pressure switch to do something? Is that the same system on the OPs setup?
Stu

Skipper

From memory there were 4 types of alternator installed on 4-108 engines They were ACS and 11AC, 15ACR and 17CR. Also some models had (I think) a Lucas (my old memory is failing me) dynamo and used to cut in around 1450rpm. Maximum output was around 22 amp at around 2250 rpm. How's that for memory!!:triumphant:

Actually I am quoting from the workshop manual I have in front of me.

"they had a crude "ignition" set up that used the oil pressure switch to do something? Is that the same system on the OPs setup" I'll check that out when I get a chance later today.

 

[William_H]

If it were my boat I would wan tthe alternator to start charging at low revs of the engine. I think 2 possibilities have been discussed. The pulley size is critical as the alternator needs to be at a suitable speed for proper charging if for instance you are topping up the batteries by leaving the engine at idle revs more alternator speed would be better. But as also said watch out for tacho calibration.
The perhaps much easier thing to check is the current provided for initial excitation. This current is often provided through the alternator light. The larger wattage the bulb the more current so the more likely you will get the alternator up and running at low RPM. I would suggest a resistor mounted across the alternator light. Typically the lamp will be 3 watt ie 1/4 amp at 12v which equates to 48 ohms so a ressistor around that amount 47 ohms will double the initial excitation current to .5 amp so possibly help things along.
good luck olewill