Ac current leak from alternator

[Mg451]

Hello all. I managed to have my main battery on off switch partially short on the open position while running my balmar 170xt alternator! So it happend 2 times opend then closed and ooend and closed by the time i was able to shut the engine down.. . Heres what i had.
Balmar xt 170 (170 amp alt) derated 40% so it maxed out at 120 ish amps. Externally regulated by a balmar mc614.
Also i have a small engine mode which takes that down another 50%( like 60amps ish) I have a sterling protecton device. To keep a load on the alternator in the event a battery dissconnect takes place.
This has worked great. I run it at 50% when im steaming or even turn ot iff via brown wie to regulate to get max h.
P. From yanmar 3gm30f.

So when the switch shorted open the sterling device tried to do its job and partially saved the alt. If i run it in out of small engine mode im getting 50amps. But in small engine mode nothing. If i put my meter in ac mode i get .34 volts ac . Ive been told this is an idication the diodes are shot or in my case some are shot and its letting some ac current past.

My question is will this destroy my electronics? Ive been running the motor woth the alt off bc im scared to destroy my electronics. And i cant really afgore another 1000alt right now. Or remove the alt to get rebuilt at the moment im living on the boat in at anchor with questonable holding i may need to motor.

[tkeithlu]

Welcome to the forum, Mg451.

Do you have any secondary means for charging your batteries? Solar, wind, genset? If you don't, consider purchase of a small generator, because you are living with no Plan B for just this sort of problem. The alternator and voltage regulator need analysis and repair, and that does involve removing them.

Alternatively, consider installation of a simple, single wire probably, alternator as a back up means of charging your batteries. That's cheap, if cumbersome.

There are people more expert than me on electrical systems here on the forum. They can speak to it. The question in my mind is that I doubt that 0.34v of AC ripple on your 13.4v DC charging circuit is going to present a problem for your electronics. Let's hear what they have to say.

[Mg451]

Yes im installing solar now and have been using the portable genny.

[BillKny]

AC ripple voltage is bad for your batteries. It causes excess heat and gassing.

How much is bad, and how bad is bad, depends on the type of battery you have:

https://www.cdtechno.com/pdf/ref/41_2131_0212.pdf

This source recommends no more than 1.5% of the float voltage during bulk charging, that would be about 0.2 volts rms.

[Jammer]

Based on the reduction in output I would conclude that the diode bridge inside the alternator has partially failed. These failures are fairly common and can certainly be triggered by shorts or opens in the output. So I concur with the local advice you have received.


Running the alternator with a partially failed diode bridge is unlikely to damage your electronics. While there will be more ripple in the alternator output, it will be mostly smoothed out by the battery. I have run alternators myself that have partially failed and have not run into problems with damage to electronics.


The bad news is that typically the rest of the diode bridge will also fail fairly quickly -- a few hours, a few dozen hours, who knows.


Your cheapest option is to find someone that will fix the alternator you already have or do it yourself. Good auto electric shops are becoming rare but if you can find one they should be able to do it. You can try to get a Balmar rectifier bridge or just put in a generic one. You could also remove the stator and bridge assembly and see if you can send it to Balmar for a new bridge. On high-amp alternators the bridges are swaged or welded to the stator which is hard to get right; solder will work but won't last as long.


If there's nothing else wrong with the alternator it would be wasteful to exchange it for a rebuilt one or to discard it for a lesser alternator. The diode bridge itself is a tiny fraction of the cost the complete assembly.

[Mg451]

Yes i see a rebuild kit is about 300 im not sure if that contains the part i need. I probably will send it out though. You say sodder will fail? Does he need to braze it or somthing?

[Jammer]

The rebuild kit contains the part you need among others, see here:

https://balmar.net/product/repair-kit-70-xt-170/

You may be able to call Balmar and just get the parts you need rather than buying a kit that contains things you don't need.

Elsewhere (in instructions for replacing the rectifier on a different model of alternator), I see Balmar recommends using high-temperature solder for the stator connections. Yes, ordinary solder melts around 365 F and weakens considerably before it reaches its melting point. The stator wires get hot enough that this is a problem, the solder softens and the wires can come loose. The auto electrical places apparently use 97% tin 3% copper solders (see here) that start to melt around 440 F.


The Balmar XT is based on the Delco AD244 and while there are important differences you may be able to find some instructions or videos showing replacement steps for the rectifier on the AD244. You do need the right kind of soldering iron and solder, and experience soldering larger wires, to do this, but otherwise it isn't a difficult job.

[Stu Jackson]

Sorry to hear about your difficulties.


Here's what I would do:


Turn off the regulator. That means the signal to the "excite" that tells the alternator to produce power is off, so it is not "trying" to provide power, it's just spinning on the belt, keeping the water pump(s) going, which is all you need until you get somewhere to fix it, or do it yourself.


With your MC-614 there are any number of different ways to do this: fuse removal, pull the power to it off the connector, etc. Simple and won't break anything.


Good luck.

[Mg451]

Thanks and yes im just gonna have it turned of via regulator until i can pull it off and rebuild. And the ac ripple is enough for me to not risk frying the rest of the electronics

[GordMay]

Greetings and welcome aboard the CF, Mg451.

A couple of excellent articles, from AMETEK ECP:

What Are The Best Materials For High-Temperature Soldering
➥ https://www.ametek-ecp.com/resources...ture-soldering

Solder Melting Temperature – What is it, and Why is it important?
➥ https://www.ametek-ecp.com/resources...-melting-point

‘KESTER’s Alloy Temperature Chart:
➥ https://www.kester.com/Portals/0/Doc...re%20Chart.pdf

[team karst]

Dont expect zero ripple from an alternator. They are 3 phase ac devices that get rectified by diodes. Although 3 phase sources are “smoother” than your fathers 60Hz selenium rectified auto battery charger, its still present.

At work, I test various industrial dc electronic devices at 10% ripple at 50/60Hz. Have not yet seen a failure.

[EngineerRetired]

I think Chris from Balmer is the go to guy. Rebuilding that alternator is not Oh My Gawd expensive and will be your best solution.