Machine Design Changes and Overload Specification

[StarCat]

I am dealing with a Berkel FMS20 stand mixer. IN the day, these units were fairly well made. With that said they are neither easy or fun to work on.
Hobart has soaked up Berkel and for those unfamiliar, Hobart is also not fun to deal with and tends to sequester and hold all Tech Data behind a firewall.
Long story, I have an older model machine that was scrapped over several major component failures, lack of a service manual, and some parts being obsoleted.
I later found a service manual, and bought a second good used machine with no problems coming in. Getting this one apart the other day I noted that a design change was made and where there once was a single pole overload [Siemens 48DA18AA4] with 25A element, they have instead installed an ABC 8 AMP ceramic fuse. There is a transformer in 120V models that provides nominal 124-150 VAC to a solid state speed control that supplies a 90 VDC motor.
Due to the extreme time involved in getting at the new design sequence, fuse......
That fuse is on the output side of the DC speed control.
It would be very desirable to install a single pole overload which can be accessed from above by simply pulling the motor, as in the older design unit. My question is would I be good using an 8 AMP element in that same overload assembly?

 

[petersonra]

If the problem is getting at the fuse for replacement, just move it someplace more convenient and extend wiring to the more convenient place.

 

[StarCat]

Its a poorly engineered affair that has to have heat shrink put back on it every time. Grossly impractical.
Yes this could be done, but the OL is much preferred.

 

[petersonra]

Its a poorly engineered affair that has to have heat shrink put back on it every time. Grossly impractical.
Yes this could be done, but the OL is much preferred.

the other option is to figure out why the fuse is blowing and fix that, or at least detect that the fuse might blow and stop the motor first.

I am not comfortable with the idea of replacing an 8 Amp fuse with a 25 Amp overload.

 

[paulengr]

Fuse DC ratings are different from their AC rating. There is kind of a rule of thumb that is a factor of two different but that’s not always true. You can’t substitute brands with DC either. So even if it says 8 A you have no idea what the DC performance is.

The trouble here is that with motor protection typically you need both. Fuses work great for short circuit protection but they are too fast for effective overload protection. And overload relays have the opposite problem. But there might be some other way they’re assuming current limiting exists, part of that updated electronics.

The fundamental issue here that if you have the motor specs we could just figure out what the correct protection is regardless of what Hobart did. But without motor data it’s all guessing,

I will say this. Typically when evaluating design A vs. B, typically operators and maintenance love the one that trips less, whether it over or under protects is not a question,

 

[StarCat]

Peter, sorry bad documentation and my bad eyesight. The overload in the old machine had a K41 trip element which is exactly right and also I was proposing installing one of 8A. So its correct and its getting installed. No idea why they would put 25A in the DOCs, but in this day and age all documentation is far worse. The fuse getting blown is most likely operator error, but this will also be sorted out.
Thanks

 

[Jraef]

Just to clear up some confusion, the Overload RELAY ITSELF is rated to handle UP TO 25A. That's not the heater element that was in it I'm sure.

The heater element that goes in it is selected based on the actual motor current. A K41 on a 48DA OL is for currents between 6.92 to 7.65 amps.

 

[StarCat]

This was my conclusion as well, but the DOCs at large do not make this clear. The Berkel OEM DOCs are also falling short on necessary information and clarity.
Thanks