alternator questions

[turf]

hey all,

i just replaced my waterpump and was checking for leaks. i started it up and the alt guage shows the voltage jumping all over the place.

i've had this problem for a year or so, intermittent wild gauges. i thought it was a loose ground wire somewhere, but it seems very basic to all electrical.

old school diesel, non electronic, cummins 5.9. last year, the last trip i took was fine during the day - i noticed the erratic gauges once in a while. and then constant at night if i turned on my headlights. at highway -wot, the lights were bright, if i took my foot off the pedal, the lights fade with the pedal.

so i just fixed a leaky water pump, and i think the alt is an issue. the belts boucne a bit, but i think this is my 3rd or 4th alternaotr with the bus. i bet i could look thru my forum post history, a new alternator will at least be my 3rd in 50k miles or so.

is there a home test for alternators? is there a specific bus alternator? the last one was a generic 5.9 dodge 350 alt.

thanks

[turf]

same problem - older thread- june of 2019
https://www.skoolie.net/forums/f39/3...why-25392.html

from that old thread, i replaced the batteries and it seemed to temporarily solve issue. the erratic gauges came back after about a month. my batteries will be going on 3 years next month. charged them last week, today the bus started on its own.

quickserve doesn't list a part number for the alt.

[PhilipE]

I would suspect a regulator problem. Your year model should be an external regulator. It should look like a Ford square body regulator. Most likely you have a Leese alt around a 150-amp rating.

To test a alt. Find the field wires. These are two small wires that should be close together coming out of the alt body. Apply 12 volts to one wire. Ground the second wire. Alt should charge full amperage and voltage. This is called a by pass test.

Here is a video of a by pass test on a GM.

https://www.youtube.com/watch?v=N1JKKUfgCtk

Your leese alt is a little different but not enough to worry about. The regulator on yours should look about like that GM regulator in the vid.

[magnakansas]

the three diodes....... these are the things that help to change the Alternating Current into Direct current. If these things go bad in such a way that they will let battery power flow into the alternator and to ground.... it is a slow leak most of the time and your batteries will drain much faster than usual when bus is parked. If a diode goes to ground in a really bad way.... the current rush is so great wires can melt and burn......

When just one diode takes a dump - the alternator can still charge but not charge very well.

How to kill a diode/alternator? while the engine is running and alternator doing its thing.... disconnect the output wire from the alternator....... not good for an alternator. another way to injure an alternator is by jump starting the bus. The kindest way - charge the batteries first then jump start if you need to.

anyways- I wonder if you have a problem with the pathway from the alternator back to the batteries... a broken wire or connector that checks good with a volt meter but is not very good under load. I have to wonder if this pathway has a problem, you replace the alternator but the root cause of failure is not being taken care of.

fusible links are often failed in such a way that the link wire is broken inside the insulation, will test okay with a volt meter when not moving gobs of current - in other words testing is done for current/voltage with engine not running..... a wiggle test often will show failure.... you have one person watching volt meter and one person yanking around on wires... I like to use older voltmeters with a needle --- you can watch the needle swing back and forth with fluctuations in voltage/current.

I am willing to lay fifty bucks that there is at least one wire, maybe more than one, that is heavily compromised. These wires are the pathway from the alternator to the batteries. It seems how many trucks are wired..

alternator to starter, there will be a fused link at the lug on the starter... then starter to batteries. often just a really big cable to the batteries... on my bus there is a lug on the frame rail. so it goes ... battery to lug, lug to starter, starter to fuse link, fuse link to alternator.

william

[turf]

i took off the alternator.

the main ground wire leaving the alternator looks suspect. the crimp on end is overly wiggly and i see some broken wires too.

there looks like a voltage regulator just down the frame rail by the turbo charger. maybe. i think it is. but idk. the part is marked with the name bosch and a partnumber 0332002155. google calls it a normally open power relay. there is another solenoid hidden next to it, but it does not appear to be wired to the alt.

i follow the alt charging wire as far back as i could. it appears to go straight back to the battery. except for the branch that comes out at the power relay above. it doesnt cross over the engine until almost past the transmission. the starter has its own big cable running to the battery box. i do not see an interconnection before the battery.

i'll take the alt to the store and have it tested. i'll get a new ground strap. and then put everything back together. if the meter goes crazy again, i'll order a new power relay.

thanks for the input!!

[flattracker]

One suggestion: If the voltage gets unstable again, test the output voltage at the alternator with a voltmeter. I the meter in the dash is changing but not at the alternator then look at wiring.

[magnakansas]

wire in a volt meter that reads positive and negative at the batteries...

there is likely a voltage regulator on the dashboard... if the dash volt meter is going crazy and the battery volt meter is stable... I think you problem is gage related.....

that bosch relay is a 75 amp relay.... dont buy a new one until you know you need to. no point in spending money that might not help your cause.

what does that 75 amp relay send power to? does is get power from the out put of the alternator?

even new parts dont work correctly sometimes.

think of these problems as sheets of paper all stacked up. until you fix the problem at the top of the stack, you dont know what is underneath for the next problem.

william

[Booyah45828]

Originally Posted by turf

is there a home test for alternators? is there a specific bus alternator? the last one was a generic 5.9 dodge 350 alt.

thanks

You can test for certain things at home.

Like magna suggested, the diodes in the rectifier could have failed, causing low output and a "surging" voltage reading. This check can be done at home with no more then an ac/dc voltmeter. Switch it to ac volt mode, and with the engine running, check for AC voltage between your alternator output and a clean spot on the alternator chassis. Anything more then half a volt of AC shows that one(or more) diodes have failed.

FYI, the number of diodes used in a rectifier depends on how the alternator is wound. Wye wound alternators will use 3, as the stator coils all share a common ground. Delta wound alternators will use 6 diodes, as there is no common ground and each stator lead is comprised of 2 coil ends. You'll find wye systems in older alternators. Most modern alternators are predominately delta wound, as they are better at producing current at lower RPM.

I believe dodge used a denso style alternator with the cummins engine, which would be delta wound. Give a link to the specific alternator you installed and I can tell you what it uses. Some alternators, like those from delco and leece, have servicable components. But some others don't. I've often found that cheap reman alternators have horrible quality. Better to rebuild your oe unit if you can.

[Booyah45828]

FWIW the headlight scenario and erratic gauges coincide with one another. Which indicates to me the dash gauge is likely fine.

As always with any electrical issue, make sure the power and ground connections are all good, clean, and tight. Resistance on the ground or power circuit can lead to a short alternator life. So when replacing the alternator, be 100% sure those circuits are fault free, or you'll be replacing the alternator again soon.

Test the batteries too. As a dead cell in one of those will also overwork an alternator.

[turf]

i have a dash voltmeter and a wired battery monitor running on a shunt attached to the battery. both gauges go wacko. the dash board needle runs back and forth, and the digital readout from the battery triggers its alarm (around 10v) and runs up to 14 in the same rapid fashion as the dash needle. numbers change faster than it can display them. i think both are fine and accurite.

the sketchy ground connection at the alt may explain the erratic reading.

the big hot wire from the alt is wrapped up in a harness. the first exit from the harness is a smaller wire going to that power relay. i assumed it was the trigger wire for the alt, but......idk. after thinking about it, it makes sense for that wire to power something else, the other direstion. maybe the power relay is a power on, for a keyed on circuit.

there is also a wire harness that comes off the alt, but i havent traced those wires yet.

we got snow this morning, slowing down my repair, the internet, and everything i do. not sure on the brand of alt. i'd have to go out in the snow and look. but here is a pic from yesterday. you can see wire exposed from the crimp connection. while the end dosent pull off, the crimp is real loosey goosey.

i'm sure its the cheapest rebuilt alt i could find. i recall paying about 130, back when i got it.

[Booyah45828]

That's a denso alternator, which is delta wound. You might be able to get a rectifier for that, just make sure it's rated high enough amperage.

Since it's already off and unhooked, I would run that to a parts store and have it bench tested. They should be able to do a diode check on the bench, and I'd guess it would show fail pretty quickly. That style alternator should have an external voltage regulator on it, either in the ecm or a self contained unit remotely mounted, but I feel the regulator isn't the problem, at least not the primary one.

[turf]

external regulator?

its an all mechanical 5.9 - no ecm and i havent found a remote voltage regulator yet.
.

taking it in for bench testing, but.... where is that volt regulator? i assumed the volt regulator was internal to the alt.

[Booyah45828]

External means theres a box somewhere that controls the alternator's power output.

Some units are internally regulated, meaning the box is a part of the alternator.

I mentioned ecm, as in electronic control module. Dodge, when they weren't equipped with an engine or powertrain control module, had a voltage regulator box mounted on the firewall that controlled the alternator. In dodges, even if it was a 6bt, it still could have had a powertrain control module, and if it did, the alternator would have been controlled by that.

You can see the plug in your picture, follow where the wire goes and it should lead you to the regulator.

[PhilipE]

Look on your radiator support. That is a common area that is used for regulator mounting point.

Look around the fluid fill points. A regulator is normally put into an easy access place. It usually isn't mounted down low on a frame. They are kept out of the weather as much as possible without putting them in the cabin.

If you see any type of small electrical box with a square cover on it. If you don't know what it is. Post a pic.

[cadillackid]

isnt that a standard SI style? with jus tthe 'S' wire used?

im used to there being more wires on an external regulator setup..

[turf]

first off, i want thank you guys for being so helpful! i appreciate it!


second, i just got back from the worst napa trip in my life.

according to my napa, the closest alternator for a 5.9 cummins is across the country in kentucky.
they couldn't figure out how to test it. they could not figure out how to hook it to the machine. after an hour of dicking around, they told me it failed and i can order another to arrive in about a week.

i ordered their suggested alt ($120), but i have little faith its correct.

[Booyah45828]

Originally Posted by cadillackid

isnt that a standard SI style? with jus tthe 'S' wire used?

im used to there being more wires on an external regulator setup..

Yeah, that actually looks like a delco 24si, which would be internally regulated.

But I don't think I've ever seen one of those used on a dodge truck. The dodge trucks I know were externally regulated, as we had to replace a pcm in one once because of a no-charge.

Dave, what number did napa order for you?

[cadillackid]

Originally Posted by Booyah45828

Yeah, that actually looks like a delco 24si, which would be internally regulated.

But I don't think I've ever seen one of those used on a dodge truck. The dodge trucks I know were externally regulated, as we had to replace a pcm in one once because of a no-charge.

Dave, what number did napa order for you?

for some reason I see Si on a lot of school busses.. not sure why but iove seen them on everything from Bluebirds to Internationals, and of course GMC..



my alternator of choosing to replace a standard mount unit with is a Bosch SB200 (School-Bus 200 amp) for any alternator that is rated less than 200 amps.. ive had great luck with them.. they can be operated with S or i wires, or as a single wire.. the part number ive used is AL9963SB.
you re-use your old pulley.. they are pretty good about producing great output even at lower RPMs..


just a thought...

[turf]

i did not see the number or alternator that they ordered. they just told me they'd call when it came in.

i tried a truck parts place in Denver afterwards and am hopeful they will find the right one. they just called back with no luck today but sending my vin and esn to their main parts warehouse and i should have the original part number tomorrow.

i havent looked to close, but that alt i have has the pulley, most of these replacement numbers do not have the pully. do i order a pulley too, or use the one off the old alt?

[PhilipE]

You would reuse your old drive pulley.

I just looked up a pic of a denso internal regulated alt. The alt you posted a pic of has the terminals in a different position. I still think you have a regulator mounted somewhere.