Weird alternator regulator problem

[cheesegas]

Thanks all. Replaced the diode pack and all works fine now. Voltage ramps up slowly to 14.4 as it did with the old Sterling, and I’m seeing 30-40a charge current when the bank is at 12.2 resting. When the engines running I no longer get the drop in current/voltage when a load is applied. 
 

I’m guessing the old Sterling may have killed or damaged the field diodes by forcing the field to full power immediately  at every startup, and as I run from solar until fairly late in the year, I didn’t notice the engine wasn’t properly charging while cruising. The solar controller took the voltage to 14.4 whenever I’ve been on the move, having been blessed with lots of sunny days and no shading on the Thames!

 

Now seeing between 1-1.5a field current which is more in line with expectations here. 

 

A side note is that the temp sensing isn’t very smart on the Sterling. Unlike other more expensive controllers, it doesn’t lower the field current slowly to find a happy medium, it simply goes 100% hands off until the temp drops. Found out by popping the sensor in a mug of hot water. 
 

[nicknorman]

Jolly good. Still a bit surprised at the low charge current (relative to max output). Maybe you should measure the voltage at the back of the alternator B+ to ground, and also the voltage across the batteries, when it’s charging at the 30-40A. My suspicion is that there is a fair bit of voltage drop in the wiring which is limiting the current.

[cheesegas]

7 minutes ago, nicknorman said:

Jolly good. Still a bit surprised at the low charge current (relative to max output). Maybe you should measure the voltage at the back of the alternator B+ to ground, and also the voltage across the batteries, when it’s charging at the 30-40A. My suspicion is that there is a fair bit of voltage drop in the wiring which is limiting the current.

I've checked that, when I installed the VSR a few months ago I replaced the alternator to starter cable and re-crimped the starter cable ends. It's a short run of chunky 50mm cable, less than 0.05v drop between B+ and starter battery positive when the alternator's working hard. The VSR has a 0.01v drop across it and its cabling to the furthest domestic battery, so that's all fine.

[nicknorman]

6 minutes ago, cheesegas said:

I've checked that, when I installed the VSR a few months ago I replaced the alternator to starter cable and re-crimped the starter cable ends. It's a short run of chunky 50mm cable, less than 0.05v drop between B+ and starter battery positive when the alternator's working hard. The VSR has a 0.01v drop across it and its cabling to the furthest domestic battery, so that's all fine.

How about the negative side of things? Any voltage drop between alternator case and battery negative?

 

My point is that with a 75A alternator connected to batteries starting at 12.2v, I’d expect 75A or so of initial charge current - presuming the rpm was enough.

[cheesegas]

Just now, nicknorman said:

How about the negative side of things? Any voltage drop between alternator case and battery negative?

 

My point is that with a 75A alternator connected to batteries starting at 12.2v, I’d expect 75A or so of initial charge current - presuming the rpm was enough.

Same, it's all nice new shiny cables on the negative side on clean studs, around 0.02v drop from alternator negative to furthest negative leisure battery. I'm thinking it may not be a 75a regulator.

[Tony Brooks]

As I think I said earlier, my Paris-Rhone 70 amp job would charge at 80 amps for a few minutes upon first starting. I think you must have volt drop somewhere or some other weird problem unless you are correct that it is not a 75 amp alternator. The regulator only deals with voltage, not currant. The current capacity is inherent in the alternator design.  If this is an A127 alternator then they were only 50 amp machines so if it has been rebuilt it could be almost anything. It would not surprise me if some were only 45 amps.

 

[frangar]

4 minutes ago, Tony Brooks said:

As I think I said earlier, my Paris-Rhone 70 amp job would charge at 80 amps for a few minutes upon first starting. I think you must have volt drop somewhere or some other weird problem unless you are correct that it is not a 75 amp alternator. The regulator only deals with voltage, not currant. The current capacity is inherent in the alternator design.  If this is an A127 alternator then they were only 50 amp machines so if it has been rebuilt it could be almost anything. It would not surprise me if some were only 45 amps.

 

I brought a A127 alternator from eBay that was sold as a 70A model but when fitted it rarely produced more than 50A….wasn’t worth sending it back..just got another one from a local recon place…although in fact it was a brand new unit. 

[Tracy D'arth]

7 minutes ago, Tony Brooks said:

As I think I said earlier, my Paris-Rhone 70 amp job would charge at 80 amps for a few minutes upon first starting. I think you must have volt drop somewhere or some other weird problem unless you are correct that it is not a 75 amp alternator. The regulator only deals with voltage, not currant. The current capacity is inherent in the alternator design.  If this is an A127 alternator then they were only 50 amp machines so if it has been rebuilt it could be almost anything. It would not surprise me if some were only 45 amps.

 

I have never seen a 75A A127 alternator in over 40 years boating, they were commonly only 45A. Bigger alternators on cars were in the beginning more often than not Bosch or Paris-Rhone.

[cheesegas]

6 minutes ago, Tony Brooks said:

As I think I said earlier, my Paris-Rhone 70 amp job would charge at 80 amps for a few minutes upon first starting. I think you must have volt drop somewhere or some other weird problem unless you are correct that it is not a 75 amp alternator. The regulator only deals with voltage, not currant. The current capacity is inherent in the alternator design.  If this is an A127 alternator then they were only 50 amp machines so if it has been rebuilt it could be almost anything. It would not surprise me if some were only 45 amps.

I bought it from a specialist alternator house in London, Unistart, who said it was a refurb unit built to 75a specification by themselves, albeit with a Chinese case. There's very little voltage drop (0.02-0.05v) across the system under load, even when measured from the furthest leisure battery (yep, I know, unequal lengths! Going lithium in the next few months hopefully) as a point of reference, this was the first thing I checked, and much of the wiring is new.

[Tony Brooks]

Just now, Tracy D'arth said:

I have never seen a 75A A127 alternator in over 40 years boating, they were commonly only 45A. Bigger alternators on cars were in the beginning more often than not Bosch or Paris-Rhone.

 

All I can say is that I have seen them advertised and not just on Ebay style scammer sites. Anyway, we don't know what alternator the OP has.

[frangar]

2 minutes ago, Tracy D'arth said:

I have never seen a 75A A127 alternator in over 40 years boating, they were commonly only 45A. Bigger alternators on cars were in the beginning more often than not Bosch or Paris-Rhone.

I have a 70A A127 unit….fitted with an adverc reg I often get 65A-75A when the batteries are down…with the adverc that is often for a while too. 

[Tracy D'arth]

Just now, frangar said:

I have a 70A A127 unit….fitted with an adverc reg I often get 65A-75A when the batteries are down…with the adverc that is often for a while too. 

I bow to your experience. 

[frangar]

Just now, Tracy D'arth said:

I bow to your experience. 

They were commonly fitted to diesel discovery’s with the TD5 & 300tdi engines amongst other vehicles. 

[cheesegas]

Also, I've checked alternator RPM with an no contact optical tacho on the pulley, it doesn't change whether it's on/off load which eliminates belt slip. Disconnected the exciter feed from the panel bulb to check. Can't remember the speed offhand but it's around 2500rpm with the engine idling at 1000rpm.

 

 

1 minute ago, frangar said:

I have a 70A A127 unit….fitted with an adverc reg I often get 65A-75A when the batteries are down…with the adverc that is often for a while too. 

Correct me if I'm wrong but the Adverc doesn't kick in until the batteries hit 14v, upon when it cycles between 14v and 14.4v every 15-20 min?

 

 

1 minute ago, frangar said:

They were commonly fitted to diesel discovery’s with the TD5 & 300tdi engines amongst other vehicles. 

Yep, my old 1980 Series III has a 45a A127. Pretty common amongst most BL vehicles I think.

[frangar]

2 minutes ago, cheesegas said:

 

 

Correct me if I'm wrong but the Adverc doesn't kick in until the batteries hit 14v, upon when it cycles between 14v and 14.4v every 15-20 min?

 

That’s right although I had mine built & set up from adverc with trojans in mind so it cycles between 14.4 & 14.8v.  A byproduct If you like of the higher voltage is a higher current too so the alternator runs harder for longer. Hence seeing the max current for a longer time. 

[Tony Brooks]

2 minutes ago, frangar said:

That’s right although I had mine built & set up from adverc with trojans in mind so it cycles between 14.4 & 14.8v.  A byproduct If you like of the higher voltage is a higher current too so the alternator runs harder for longer. Hence seeing the max current for a longer time. 

 

But only AFTER the inbuilt regulator starts working. Before that the inbuilt or external regulator can do nothing,

[frangar]

5 minutes ago, Tony Brooks said:

 

But only AFTER the inbuilt regulator starts working. Before that the inbuilt or external regulator can do nothing,

Yes. I should have said The adverc is in addition to the built in reg. 

[nicknorman]

19 minutes ago, cheesegas said:

Also, I've checked alternator RPM with an no contact optical tacho on the pulley, it doesn't change whether it's on/off load which eliminates belt slip. Disconnected the exciter feed from the panel bulb to check.

 

There is something wrong with this, if I understand correctly what you are saying. Disconnecting the "exciter feed from the panel bulb" will have absolutely no effect when the alternator is running. When running, all excitation current is provided by the field diodes. Both ends of the panel bulb are at the same voltage, so no current flows through it, hence it is not lit, and hence disconnecting it will do nothing!

 

Well that is, unless it is a 6 diode machine which means it isn't an A127

 

Also, you mention 1 to 1.5A field current. This still seems low to me. According to Mr Google the resistance of an A127 rotor is around 3 to 4 ohms, therefore one would expect a max field current of around 3.5 to 4.5A. If 1 to 1.5A field current gives you 35A or so, no doubt 3.5-4.5A would give you the expected 75A. Something is not adding up.

Edited November 8, 2021 by nicknorman

[cheesegas]

Just now, nicknorman said:

 

There is something wrong with this, if I understand correctly what you are saying. Disconnecting the "exciter feed from the panel bulb" will have absolutely no effect when the alternator is running. When running, all excitation current is provided by the field diodes. Both ends of the panel bulb are at the same voltage, so no current flows through it, hence it is not lit, and hence disconnecting it will do nothing!

 

Well that is, unless it is a 6 diode machine which means it isn't an A127

Sorry, I should have clarified, yep I know the exciter feed only carries current when the ignition's on and the engine is not running. Started the engine, checked RPM/charge current with a clamp on the alternator cable. Stopped the engine, disconnected the exciter, started the engine. Zero charge current as the alternator's not self exciting, checked RPM.

[nicknorman]

2 minutes ago, cheesegas said:

Sorry, I should have clarified, yep I know the exciter feed only carries current when the ignition's on and the engine is not running. Started the engine, checked RPM/charge current with a clamp on the alternator cable. Stopped the engine, disconnected the exciter, started the engine. Zero charge current as the alternator's not self exciting, checked RPM.

OK fair enough, also see my edited addition to previous post. (you were too quick for me!)

[cheesegas]

7 minutes ago, nicknorman said:

Also, you mention 1 to 1.5A field current. This still seems low to me. According to Mr Google the resistance of an A127 rotor is around 3 to 4 ohms, therefore one would expect a max field current of around 3.5 to 4.5A. If 1 to 1.5A field current gives you 35A or so, no doubt 3.5-4.5A would give you the expected 75A. Something is not adding up.

 

Surely the field current controls stator output voltage, so if the Sterling is seeing 14.4v at the batteries it won't increase the field any more? Definitely an A127, and slip rings/brushes are in good order.

 

(not being difficult here, just what I'm thinking!)

[nicknorman]

5 minutes ago, cheesegas said:

 

Surely the field current controls stator output voltage, so if the Sterling is seeing 14.4v at the batteries it won't increase the field any more? Definitely an A127, and slip rings/brushes are in good order.

 

(not being difficult here, just what I'm thinking!)

Yes, but what voltage at the batteries are you seeing when you've started with them at 12.2v and are initially getting 35A? If 14.4v then I agree. But that rather points to batteries that are seriously knackered! If on the other hand you are getting the 35A with perhaps 13.6v or so, something is lacking in the field current department.

 

For comparison, when we had 450 Ah of LA batteries, 14.4v across the batteries starting from 12.2v would give me the full 175A or even 185A if the alternator was cool.

[cheesegas]

8 minutes ago, nicknorman said:

Yes, but what voltage at the batteries are you seeing when you've started with them at 12.2v and are initially getting 35A? If 14.4v then I agree. But that rather points to batteries that are seriously knackered! If on the other hand you are getting the 35A with perhaps 13.6v or so, something is lacking in the field current department.

 

For comparison, when we had 450 Ah of LA batteries, 14.4v across the batteries starting from 12.2v would give me the full 175A or even 185A if the alternator was cool.

I'm seeing 12.2v resting, 13.6v as soon as the engine starts which increases to 14.4v within 1 minute of the Sterling kicking in. It waits for a bit after the engine starts, presumably to avoid belt slippage. Charge current is then 35a.

 

Batteries are probably rather tired, been in the boat since March but they're 4 years old, taken from a project at work after I was done with them! I wouldn't expect them to accept a high current charge to be honest.

[MoominPapa]

1 hour ago, Tracy D'arth said:

I have never seen a 75A A127 alternator in over 40 years boating, they were commonly only 45A. Bigger alternators on cars were in the beginning more often than not Bosch or Paris-Rhone.

I've just fitted an A127 marked 75A that I bought as a spare/standby from Ebay about five years ago. It does indeed produce 75A (actually 80A when cold).

 

MP.

[nicknorman]

4 minutes ago, cheesegas said:

I'm seeing 12.2v resting, 13.6v as soon as the engine starts which increases to 14.4v within 1 minute of the Sterling kicking in. It waits for a bit after the engine starts, presumably to avoid belt slippage. Charge current is then 35a.

 

Batteries are probably rather tired, been in the boat since March but they're 4 years old, taken from a project at work after I was done with them! I wouldn't expect them to accept a high current charge to be honest.

 

OK well in that case it sounds as though the batteries are knackered. Of course you will have the opposite problem if you switch to Lithiums, the alternator will be running flat out and getting hot. Hopefully the Adverc will protect it!