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Alternator BBQ.


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Something strange going on. Our 120amp bosch alternator runs OK at first then the voltage drops, so does the current and it starts heating up...lots. It's controlled by one of Graemes ZM4s so been in touch with him but would love to get some ideas from the experts in here? We did have the battery sense wire 250ma fuse pop a few weeks ago so Graeme said put a 1amp in which we did and also crimp soldered the battery sense wire direct to a main battery cable. I am pretty sure the bosch is toast. Maybe one of the diodes has popped but it seems strange that over night voltage drops to 12.2 (with all this bloody cloud and no wind!) so start the engine and using the regulator set the voltage on 13.6 for a while charging 4 x 65ah SLAs at about 20 amps. Then bring it up to about 13.8 then 14.1 then to 14.4v. All goes swimmingly charging at about 30 amps. After about 5 minutes down the voltage goes all by itself to 13.6v and 18amps and the alternator is now a bbq.

Going to have a play with it this morning, see if there is any reverse leaking through the rectifier and AC between the battery terminals. I run the engine at 1200rpm when charging incase you were wondering.

Thanks for any ideas and enjoy the turkey and cake!

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Sounds like alt is working hard. Put a clamp meter on the alt output and check it. Most of those bosh units had internal temp sensors, but that should be bypassed with external regulation.

I have seen the fans installed backwards! they need quite a bit of air to cool.

Batts should be accepting way more than 30a at those voltages.

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Thanks for looking at this Matt. Below is what I sent to Graeme this morning:

 

Before starting the engine I put the clamp meter over the +'ve and discovered a residual current of 0.3amps so I think a diode has gone faulty current shouldn't flow back through it? Started the engine with batteries floating voltage at 12.3.

 

I put a clamp meter over the output and charging at 34amps, 13.7v. Left it there and alternator just warm. Wound potentiometer up to 14.0v and charge rose to 39amps. Freezer switched on and alternator immediately began over heating and voltage dropped to 13.8. I quickly turned the freezer off and alternator cooled down and voltage at 14.1 23amps. Left about 10 minutes then turned freezer back on and voltage stayed at 14 no over heating.

 

It would appear the alternator can only do a max of 40amps then heats up. Checked AC output, only a small residual current of about 0.03amps which is what I would expect with no capacitive filtering.  What confirms my suspicions is the freezer pulls just over 4 amps and the alternator is able to slow a 18hp diesel at 1200rpm when it switches on! You can hear the engine load up. 

 

We used to be able to charge the batteries and run both fridge and freezer that pull 8amps combined plus charging 240ahs of battery from a start average of 12.5v. Now it can't.  

 

Hope that gives you some clues? Here we were thinking it was the sense wire not connecting properly but that's not the case. This all started after the 250ma fuse popped in the 'batt' supply sensor to the ZM4. The 1amp fuse is still good

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Check the reg cables for voltage drop, but it sounds like the alternator is toast. If you remove the field connection, jump alt field to the batt + terminal. Now the alt is told to go full throttle. What's the amps? Volts won't be regulated, so don't do it for long!

Compare amps to alt spec...

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Check the reg cables for voltage drop, but it sounds like the alternator is toast. If you remove the field connection, jump alt field to the batt + terminal. Now the alt is told to go full throttle. What's the amps? Volts won't be regulated, so don't do it for long!

Compare amps to alt spec...

I can smell the smoke already!! It's a 120amp alternator and its maxing out at 40 amps which means only one phase is operating? Makes sense...it's toast!

There is a slight back current leaking through the rectifier so my thinking is diodes. Only lasted 150.7 engine hours! Brand new.

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The small frame Bosch 120 amp alternators aren't very robust.

We fried about one a year while doing our circumnavigation.

We were told that they were developed for auxiliary lighting on tractors and the like. No idea if that is correct.

The advantage was the very low price compared to the large frame "marine" units of similar output.

150 hours is pretty poor however.

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You still up in Whangaroa CH? I'm in auckland tho.

I have a coupla spares here. A hitachi 55A factory or a new Delco 10si clone you

could use until you sort yours.

The 10si was an experiment but overheated too fast at 120A. Both 115mm dual foot.(Yanmar)

Just a stopgap.

 

Wow! Thanks but all good til Graeme has caught enough fish and gets back to work again at "smart regulator". Have decided to buy one of his refurbished alts and ask him to send that to us then return this to see whats gone wrong, get it repaired and keep it as a spare. It still charges at 14.1v 30amps so cloudy days we can still keep the beer chilled! Currently tucked in around Butlers Point in Mangonui then soon off to Houhora but I like your offer, much appreciated! Glad to see the bloody rain has gone.

Dam, just re-read your post. What is the clone!? I searched everywhere before getting the bosch and Graemes adaptor mounting kit and could find nothing other than the Hitachi that fitted the 115mm mount! The same 55ah one we already had that comes with the yanmar that maxed out at 13.6v and charged nothing properly.

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My experience of this is that the Bosch and Hitachi units are not great for external regulation, they often fail due to heat. They are not hot rated.

Graeme will tell you Hitachi is ok, but not many of his regs are on offshore boats with large banks. If you drive the Hitachi's near max output for multiple hours, they melt.

My advice would be to find a hot rated unit.

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Thanks. I keep an eye on the volts when underway anyway, more so since it tried cooking. When I ran it at 30amps the fan was extracting the heat OK but I am now thinking whatever else I get from Graeme I will fit a blower to the rear of it and a temp alarm! Probably a good idea to have all round in the engine bay. Fashion a cowling out of fibreglass to go over it.

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10SI clone

 

I have cut the ground leg on the internal reg and run a wire for ext regulation.

But it does not have the heat dissipation ability of the  bosch AL170X (Reman)

So not a permanent solution. Only a door stop here so you are welcome to it.

 

There are several numbers that will fit the porsche 944. All you cut have to cut off

2mm of boss on one of the legs  and pack with washer to align with standard yanmar

crank pulley. Easypeasy. Oh, and replace factory brushset/internal reg with brushset only

for external regulation.

Where did you get it? Looked on line and can't find anything.. I think you and IT are right, need to go to a heat capable alternator.

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Enertec have the leece Neville (sp ?) Range, with some good alts under $400. The issue is that they are large frame alts, so may need a custom mounting bracket. But they are hot rated, and will put out their rated amps indefinitely.

Imo this is a critical system on a livaboard.

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I think I've found the problem!

The alternator relies on the fan to draw air through it, there is no other source of cooling for ours (to be CHANGED!). RAN the buggar just a while ago this morning for about 15 minutes at about 1200rpm and 40 amps at 14.5v. After about 5 mins, my hand on it, it started to warm up, I could feel hot air coming out of it. Bought the revs up to 2K and she cooled down! More air being drawn through the alternator. So, if our batts are low from over night, obviously the alternator is going to be under more load to start off with so idle is the killer? I am sure its lost a phase or probably 2 as the analogue volt meter moves a fraction to the rhythm of the engine which I am sure is only one turn operating. The diodes on the other 2 must be poked. What do you think IT?

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Sounds to me like the alt has lost 2 phases. Interesting about the air flow. Heat is what kills many alternators, and there are duct kits around for some models, and a few generic ones. My experience is that well designed alts don't need them though. They can help on one thats not really up to the job! Hitachi units have thermal output control with their standard regs, and will cut back their output pretty fast due to heat.

Be interesting to look inside your alt to see how hots its got - thats likely what killed the 2 phases..

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Have a digital thermo thats been sitting in the bow junk box and decided to stick the little probe suction cup on the alt. Interesting! 1200rpm, charging 13.8 which crept up to 14.1v at about 30amps. Temp rose to 34c in about 10mins and could smell burning! Bought revs up to 1900 and temp drops to 32, no more smell. Back to idle then shut down. No smell but watched temp rise to nearly 40c! OK, that's not "hot" but whats going? The alternator is definitly poked, that I know, just seems strange!

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