# Forklift Battery charger rebuild



## Jay Freeman (Aug 2, 2017)

One of the 48v forklift chargers stopper working and after checking, I found the 300amp fuse blown due to a few shorted power diodes in the rectifier array.

The model is CR24FR3B-850

According to Crown Battery .com, this charger is discontinued and there is no parts list available.

I hate to throw it away though. I'm thinking about just getting a larger heat sink and mount some generic power diodes.

The original diodes are not the type that I usually see. Crown took 3 small diodes instead of just one large diode and then arranged them in parallel on one heat sink panel and then sandwiched 3 more of these array panels for a total of 12 diodes where they could have just used 4 large power diodes. I have a picture of the complete array but I don't have permission to add attachments.

Anyway, I'm just wondering if anyone has some suggestions on which 4 power diodes I should use. The manual doesn't give any technical specs on the original diodes so I don't exactly know how much current they passed.

The charger sticker states that the DC output is 48v at 162amps.

The charger power input is 480v 3 phase. I'm not exactly sure how the charger rectifies this and which diodes pass which parts of the half wave. I'm more familiar with single phase FWB rectifiers.

Any help is appreciated,
Jay


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## MDShunk (Jan 7, 2007)

Your description of paralleled diodes sounds pretty normal in my experience. Just cross them over at your normal electronics supplier like Allied Electronics, Newark, or DigiKey. I work on lift chargers as a normal function of my present job. Replace ALL of the diodes as a set, and do all of the SCR's at the same time.


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## joebanana (Dec 21, 2010)

Just your basic 3 phase rectifier. (Google it) They probably paralleled the 3 diodes because it was cheaper than 1 162 amp @ 48v. diode. Better heat dissipation too.


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## Jay Freeman (Aug 2, 2017)

MD,

These small diodes seem to be pressed into the aluminum sink plate plus the ceramic insulators are cheap and about 5 are broken. It's just doesn't look like a good design.

Joe, 
I'll see what I can find out. Thx


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## Jay Freeman (Aug 2, 2017)

Joe, 

From what I can see, a 3 phase rectifier needs 6 diodes but this charger only uses 4.

However, I did find 200A power diodes on Ebay for $23 each.


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## MDShunk (Jan 7, 2007)

Jay Freeman said:


> MD,
> 
> These small diodes seem to be pressed into the aluminum sink plate plus the ceramic insulators are cheap and about 5 are broken. It's just doesn't look like a good design.
> 
> ...


Pressed? Doubtful. They ordinarily have a threaded stud. You need to make a custom "oxygen sensor socket" to take them out, normally.


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## Jay Freeman (Aug 2, 2017)

You can see those 3 circles in the top picture, are the pressed in diodes.


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## MDShunk (Jan 7, 2007)

That's weird, but plenty of meat to drill and tap for a normal diode and run a pigtail from each one over to that binding post . 

I wonder if the OEM intends to sell that as an assembly; the whole plate with diodes installed as a replacement part?


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## Jay Freeman (Aug 2, 2017)

From what I was told by Crown, yes, the whole unit was sold as one part when it was available.

I can put 4 high current diodes in place of the arrayed diodes but I wonder if that heat sink plate would dissipate the heat adequately enough since all the heat would then be concentrated in a much smaller area. I can see the advantage of these 9 small diodes acting as one diode on each plate, in regard to heat management.

I'm thinking I'm going to have to get a beefier heat sink for the conversion over to 1 diode per plate.


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## MDShunk (Jan 7, 2007)

Jay Freeman said:


> I'm thinking I'm going to have to get a beefier heat sink for the conversion over to 1 diode per plate.


Or, you could buy a new lift charger? Or a used one. Industrial surplus dealers sell them for a fraction of retail every day. At some point you need to decide if the juice is worth the squeeze.


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## just the cowboy (Sep 4, 2013)

How old is it? Filter caps may be ready to go also due to age.


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## 460 Delta (May 9, 2018)

That looks similar to the rectifier unit in Lincoln Idealarc welders. You might hit up a welding machine repair shop, just a thought.


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## Southeast Power (Jan 18, 2009)

You are going from a production array to a custom array. If you are comfortable with doing the work yourself, swap out the three small diodes for two full size diodes. The cost will be minimal but it will never again be the diodes.
10/10 would replace the SCRs and the filters while you have it opened up.


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## Almost Retired (Sep 14, 2021)

HenryBallard said:


> That's too hard to rebuilt it without a specialist.


i wish you had not waited 4 years to tell them


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