Jump to content

Isuzu Domestic Alternator


Featured Posts

Hi All,

 

I'm after a little advise about my replacement alternator, Pestolite 66021590M, which  I have fitted. It is replacing the original 900021-als with is a Lucas a127 70amp which was teamed up with Sterling Advanced Regulator ( the blue one).

 

This is a photo of the old alternator in situ.

1945476000_WhatsAppImage2020-05-05at08_30_15.jpeg.2aaba074cac228c0d12e7894af73f18a.jpeg

 

Looking at the HMI diagram (attached) the old alternator doesn't have a negative connection, so assuming the case was the negative.

 

On installing the new alternator I connected the Black & Yellow cable (D+) which connects to the Aux Light on the control panel and the battery plus (B+). 373399279_WhatsAppImage2020-05-05at08_28_26.jpeg.5a5faf624a97ce073929ac275a50069d.jpegprestolite_66021590m.jpg.8050065cc8aeaf62f232eb08753fb8d7.jpg

 

Turning the ignition to the on position the the 'Aux Alternator Charge Light' on the control panel did not illuminate as it normally would so I touched a cable between the battery negative (B-) and the engine casing, instantly the light illuminated indicating to me that i need the negative connection.

 

The next test was to briefly turn the engine over and jump between the B- and the engine casing. No output from the alternator until the jump was made which shot up to 88 Amps and the engine tone changed to indicate a load. Using a bit of 6mm cable I connected the B- to the negative on my batteries using ring connections, I turned the engine over, keeping an eye on the cable temperature, the charge rate was significantly lower about and Amp (forgot to write it down) and with the inverter running the batteries we discharging. 

 

The batteries were almost fully charged (~98%) but I would have expected with the inverter & TV one the the charge would have been positive. What am I missing or doing wrong?

Also, I am unsure what the negative cable should be, is it just completing the circuit or is it taking a heavy load therefore needing a heavy duty cable?

 

Any views / suggestions / ideas / pointing out my mistakes would be great,

 

Thank you,

 

Scott 

 

 

image.png

66021590M_wiring.jpg

Link to comment
Share on other sites

Clearly by the size of the connection (B-) it is not designed to take the full alternator current or it would be the same size as B+. Maybe it should be connected to the -ve of the battery as part of the sense circuit. Normally the hull, engine and the negative terminal should be at the same potential so connecting to either one shouldn't make any difference. Some of these Isuzu connections are poor so check the negative connections from the battery to the engine and the black wire from the harness to the engine. The multipin plug can also cause problems. Hope this helps.

Link to comment
Share on other sites

Thanks guys, that’s my view on the B- too. It is only a yellow ring connector so not able to take a massive cable anyway. I’ll check negatives all the way through the circuits (domestic & starter) and I did clean up the pin connector as that has been a pig in the past. 
 

I have been draining the domestic batteries down a little just to see what happens in the bulk charge. 
 

Scott

Link to comment
Share on other sites

Not disputing this but the diagram states the B+ and B- are both M5 studs yet the photo appears to show a much thinner stud for B-. Compare the nut size in the photo between B+ and B-. Its a bit of a mystery. If it were a Lucas built machine I could understand it having suffered those 9mm main output blades but surely no other manufacturer would reduce connection sizes like that.

Link to comment
Share on other sites

As I read the diagram it says B+ positive output stud is M6 x 1.0 and B-  -ve terminal stud is M5. That looks pretty close to what is in the second picture. Not sure why the two should differ, as I would expect both to be handling the same current.

The OP problem appears twofold:

there is no connection between B- and the battery negative. 

When one is inserted the charge rate is low.

First one: Has a negative side isolator been turned off in the fitting, and not turned on?  Where does the wire from B- go?

Second one: What is the regulated output voltage now the Sterling has been disconnected. If is has a low outout voltage setting the new alternator won't put much into the full batteries, even with the inverter on (at what load?).

 

N

Link to comment
Share on other sites

Could you possibly have connected the B- jump cable to the battery + in error?

The B studs are different sizes to try to avoid them being reversed when connected I think.

The Prestolite alternator does require a B- connection, short and straight to the engine block will suffice usually with a substantial cable, 10mm minimum, 16mm better with solid ring crimps not the thin yellow crimps.

Link to comment
Share on other sites

I have a similar looking alternator and B1 has a fat cable to battery negative, it is fatter than 25mm but not sure what size. As it is carrying the full output current, any voltage across it will affect the alternator regulation, so the 6mm cable would drop a fair bit of voltage at even half the alternator output, (at full output it would melt) so fooling the regulator into thinking the batteries were full.

Link to comment
Share on other sites

I just can't get parts for these alternators. Regulator I use an A127 part which just needs fixing holes drilled out to take insulators. Rectifier, again A127 but with considerably more modification, including removing insulators from the W terminal which then becomes B-. Positive terminals being slightly larger is an old convention which used to be common on things like dynamos but the only place I can think of where it still applies as a standard is batteries though Bosch still use it for insulated return alternators.

Link to comment
Share on other sites

The B- was directly connected to the battery negative terminal. 
 

I’m yet to turn the engine over since the drain over night without wanting your advise.  
 

The thing that confuses me (not difficult when it comes to boat electrics) the most is the old alternator didn’t have the B negative so just used the mounts as the negative connection and thus the fat cable off the engine?

Link to comment
Share on other sites

You can always measure the resistance between B- and the case. Maybe it is an insulated return machine in which case B- will take the full current so you will need a cable similar to B+. I dont see why you can't just ground it to the case if you don't need an insulated return alternator.

Link to comment
Share on other sites

The old alternator was an uninsulated return with negative connectd to the case, so the cable from the engine to the battery took care of the negative.  The new one has the negative terminal insulated from the case as is good salt water marine practice. ( avoids problems  with nav electronics among other things).   That means you must provide a full output current path from B- to the engine, or to the battery negative terminal, or to the  high side of any ammeter shunt.

 

N

Link to comment
Share on other sites

4 minutes ago, swmenzies said:

The B- was directly connected to the battery negative terminal. 
 

I’m yet to turn the engine over since the drain over night without wanting your advise.  
 

The thing that confuses me (not difficult when it comes to boat electrics) the most is the old alternator didn’t have the B negative so just used the mounts as the negative connection and thus the fat cable off the engine?

I think this can be summarised as the difference between automotive and marine alternators. As a general point, marine alternators don’t have their case connected to the B-, they need a separate -ve cable. This is to be able to control exactly where the -ve current is going, to avoid any possible issues with hull corrosion. Automotive alternators tend to use the case as the -ve, via the engine etc.

 

In you case you probably have a starter motor that has its -ve terminal connected to case, so you already have the engine connected to battery negative. Having an insulated -ve alternator therefore isn’t doing much good, but no harm either. You just need a fat wire either to battery -ve or even just to a convenient point on the engine.

  • Greenie 1
Link to comment
Share on other sites

1 minute ago, Mike Adams said:

You can always measure the resistance between B- and the case. Maybe it is an insulated return machine in which case B- will take the full current so you will need a cable similar to B+. I dont see why you can't just ground it to the case if you don't need an insulated return alternator.

You coild just take the nut off the B-, remove the insulator, clean up the case, put a washer on instead of the insulator and do the nut up again.

  • Greenie 3
Link to comment
Share on other sites

Great, that explains it to me in simplistic terms!

 

I do have ‘spare’ battery connection cables but unsure if I have enough length. Might be tricky to get a cable at the present time in London. 


and I like your solution Sir Nibble. 
 

thank you all! 

Link to comment
Share on other sites

Hopefully last question before the many thanks and documentation reply. 
 

The B+ & B- has a 2.2μF capacitor between the connections. Do I leave this in place if I remove the insulator on the B-?

 

thanks, 

 

Scott

 

DD4D2C86-4C4E-4ABC-A98A-14765CC7C57D.jpeg

Link to comment
Share on other sites

13 minutes ago, swmenzies said:

Hopefully last question before the many thanks and documentation reply. 
 

The B+ & B- has a 2.2μF capacitor between the connections. Do I leave this in place if I remove the insulator on the B-?

Yes :)


Although I’m not sure what purpose it has on a Diesel engine. 
 

 

Edited by WotEver
Added the last bit
Link to comment
Share on other sites

12 minutes ago, Tony Brooks said:

Radio suppressor but not so sure how a slip ring device in good condition creates interference unless its from regulator switching.

This is how people must feel when I explain IT technical issues to them!!

Link to comment
Share on other sites

1 hour ago, swmenzies said:

Hopefully last question before the many thanks and documentation reply. 
 

The B+ & B- has a 2.2μF capacitor between the connections. Do I leave this in place if I remove the insulator on the B-?

 

thanks, 

 

Scott

 

DD4D2C86-4C4E-4ABC-A98A-14765CC7C57D.jpeg

If you leave the capacitor in it's doing nothing either harm nor good.

Ok, belay that, I was thinking of the usual practice of a cap from each terminal to earth. Yes, leave it in ?

59 minutes ago, Tony Brooks said:

Radio suppressor but not so sure how a slip ring device in good condition creates interference unless its from regulator switching.

Output ripple can effect vhf, radar or depth sounder.

Edited by Sir Nibble
Link to comment
Share on other sites

1 hour ago, Sir Nibble said:

Output ripple can effect vhf, radar or depth sounder.

True, however I can't imagine that a 2.2uF would have any impact on such a low impedance circuit if the aim is to remove the low frequency (ie rpm x poles) ripple.

2 hours ago, Tony Brooks said:

Radio suppressor but not so sure how a slip ring device in good condition creates interference unless its from regulator switching.

Even regulator switching isn't really "hard" because when the regulator switches off, the field current doesn't stop, it continues to circulate via a diode.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.