Help with 110-555 alternator

[madlabs]

Hi All,

I'm having problems with a 110-555 alternator. At first, as I reported on these forums, I thought it was the motor powering it. Now however, I have gotten a tach working correctly for the motor and I am getting proper RPM. So now I need to rip into the alternator. The closest place I can get it tested is a 3 hour round trip, so I'm going to have to do it myself.

So, how to test the diodes? Can I test them in place and connected? I understand the diode leads are welded in. Any tricks/tips about taking it apart?

Bob G, you said something about aftermarket diodes for this alternator. Can you give me any details? If you (or anyone else familiar with this alt) could drop me an email that would be great, I'm not sure how interested the rest of the forum will be. My addy is jpeakall AT madlabs DOT info

I'm bummed it's the alt and really don't get why it would have blown. I never pulled more than 120 amps from it and never ran it without a load connected.

Thanks!

Jonathan

[Flux]

You can test for a shorted diode with the thing still connected. You won't have more than one shorted one and have it still sort of working.

A multimeter will reveal a dead short diode as a short in either direction if you reverse the leads.

Without a lot of confusion you will have to break the ac connections to the winding to test for open circuit. You need to remove at least 2 of the ac connections.

The diodes should then test as diodes with a high and low reading if you reverse the leads.

Quite likely the connections are spot welded or brazed. If you don't have proper facilities then the best you can do for your application is to clip the ac leads and solder leads to the alternator winding. You could then solder these to the diode pack or to an external diode bridge if you decide to replace the internal ones. Remember you are dealing with heavy current and you need sensible size wire and good solder connections.

From what I can remember of your symptoms you may have an open circuit diode or you may have something limiting the field supply, I can't remember if you are using the regulator or have bypassed it. You can always check that you have the full field volts on the slip rings.

I don't have any detailed knowledge of your alternator, they are not common here but basically they are all the same in general construction.

There are 3 small diodes as well as the 6 main ones and these form part of the internal regulator circuit. If you are using the internal regulator failure of these will cause trouble and you need to check them. If you are supplying the field direct then only the main 6 diode bridge are being used.

Flux

[bob g]

to add to Flux's comments

and i too have lost track of what all you have done with the alternator, but

first things first

i seem to remember you haveing a oscope

you might want to take a look at the output waveform on the scope

if you have a bad diode i would expect a bad blip periodically on the waveform?

if you feel you must open the bugger up

remove the front half of the housing leaving the stator in the back half

the remove the stator from the rear half, it is retained by 3/8" hex nuts, on 3/16 or #10 studs that pass thru to the outside that make the AC posts. remove the inside nuts and lift out the stator.

look over the stator well, i don't expect any problem with it, but look it over just the same.

the rectifier bridge has all the diodes welded in jumpers making seperation near impossible, so you can only check one side of the other, and not isolate a specific bad diode.

they are press in .500 diode, i use 570 and 572's which are 70amp and 200piv rated units standard high power silicone fast recovery,, the oem's are using avalanche diodes that clamp at about 30vdc.

usually if you test the AC posts, 1-2, 2-3, 1-3 and all the voltages are the same

the diodes are likely just fine.

too bad you don't live closer, hard to diagnose problems online

if after all this you find bad diodes, either limit the output current to no more than 100amps continuous or get the thing mounted so the fan turns the right way, or

get a reverse rotation fan... and then limit it to 120amps continuous.

and then only if you are spinning it upwards of 4krpm

lastly if the machine has been damaged due to overheating, forget the darned reostat control, you have no way of knowing what is happening with a reostat unless

you are sitting in front of the ampmeter with the dial in your fingers, walk away

and anything can happen. someone throws a load on the batterys, and your 100amp

setting of the reostat not becomes 140 or max output for the alternator,,, how long

that load stay's on is anyones guess, and certain overheat is the result.

far better to use the oem regulator until you get your controller working or buy a suitable controller that has an alternator stator/case temp sensor to protect the alternator.

bob g

[Flux]

If you have a scope and you are feeding the field via a rheostat there is a trick with large alternators that may work, I don't know if it is effective with a car alternator as I have never tried as there are infinitely easier methods for those familiar with the things.

On large industrial alternator exciters which are feeding rectifiers a faulty diode kicks back a ripple into the exciter field. This can be used to monitor for diode failure.

If you have some rheo in circuit and you look at field current ( voltage across the rheo) you will probably see a small and symmetrical ripple in the current. A shorted diode will give a very large chunk of ripple at once per cycle of the main frequency. An open circuit diode will do similarly but the ripple will be much smaller.

The ripple that you see is normally at 6 times the alternator frequency, small and completely symmetrical. Any lumps or lack of symmetry is very suspicious and should make you suspect a diode fault.

As bob g said much of this comes down to practical experience and without that experience it will take a lot of questions backwards and forwards to get you thinking on the right lines.

I would have thought your simplest option would be to replace the internal bridge with a good reliable external one and one in which you can separate the connections for testing. The internal diodes are not really intended for user repairs and you can't really do simple tests without disconnecting them, there are too many feedback paths to do it with a meter unless you are familiar with the side effects.

Flux

[madlabs]

Thanks for all the info guys. Sorry it took me so long to get back to you, I did a 48 hour shift, came home, passed out, and am now heading out for another 24 hour shift.

I'm not as convinced that it's the alternator. I connected the old 60 amp alternator back up to the motor and now I have to rev the engine much higher to get my accustomed 50 amps out of it. I don't know what the heck is going on now.

I have another motor, so Sunday I'm going to set up the 110-555 on it and see what I get. I'll start with the oscope tests and see what I get and then go from there.

Thanks again for the help, I think with the info y'all just gave me I should be able to figger out what is going on.

Jonathan

[Flux]

I cant remember much of the details but to me this seems a classic case of belt slip.

Flux

[cyplesma]

the first thing I always suspect when it comes to alternators is the bearings. They don't always make noise when they go bad, but hopefully the motor has a half way decent muffler on it so you might be able to hear the bearings if they are making noise. I've killed a few alternators in non automotive setups due to the alternator not being as inline with the belt as it should be.

[bob g]

normally i would not suspect brgs as being a problem, this was a new unit

and has very low hours, the unit also uses very large ball brgs front and rear

but...

(always a but)

he does have it mounted vertically, i have no idea how the brgs hold up with vertical mounting,, i would expect them to last for several hundred hours though

i think Flux has it nailed down, most likely belt slip

i don't recall what drive he is using, for all i know he is using a fractional hp

belt and aluminum pulleys?  if so its a wonder it works at all.

hopefully this is not the case, one way to find out quick

run it up under a load for a minute of two, then shut down and touch the pulley with wet fingers (quickly)

if they are slipping they will be very hot and will blister your fingers, so maybe

this is not a good idea if you aren't used to moving fast.

use your laser temp gun

bob g

[madlabs]

Well, it doesn't seem to be belt slip. On the 50 amp alt, I use a single A belt. It wears out belts faster than I'd like, but we are talking at least a couple hundred hours per belt.

The 160 amp alt uses dual A belts. Don't really know about belt wear yet. All the pulleys are cast, purchased from Burden Sales and Surplus. Great place, BTW.

Since I have the 50 amp mounted, I'm working on another mount for my other identical motor. I'll see if it runs better with the other motor, and then I can look at the output of the big alt and see what I see.

Sorry again for the long delay in replying, I do really appreciate the help.

Jonathan

[dnix71]

Hey, Jon. Glad to hear you have work, even if the shifts are long. California is basically broke, it seems.

I have a 1 wire 12v alternator (supposed to be 100 amps or so) I've never used. If you want it to play with, send me an email. It has a regular v-belt pulley.

Your 110-555 is normally 24v, I don't have anything like that laying about.

[madlabs]

David,

You bet I'm glad to have work and California is broke. I was a science teacher and Vol. firefighter before the budget fiasco. Now I work on an ambulance and fill in at a paid fire dept. Glad I had some recession proof skils.

You have already been so generous I feel a little guilty taking you up on your offer, but I will anyway. As long as you let me pay the shipping this time. I'll drop you an email.

Thanks for your help and kindness once again!

Jonathan