# Jumper out 1 ohm resistor?



## MikeFL (Apr 16, 2016)

You say it's a vital system in a hospital.

Is someone going to die if it fails?

Is someone going to die if you don't get it operational?

What is the system?


----------



## gpop (May 14, 2018)

Have you got any resistors you can parallel to change the ohms.


----------



## gpop (May 14, 2018)

MikeFL said:


> You say it's a vital system in a hospital.
> 
> Is someone going to die if it fails?
> 
> ...



Dan foss so its most probably for the aircon.


----------



## BrightLight9 (Jun 10, 2018)

I recommend you to find other board and check the resistors out. How did you know they were 1,37 Ohm if they blew up? It looks like something else was damaged on board.


----------



## farlsincharge (Dec 31, 2010)

It's for the AC in long term care. Supposed to get hotter at the beginning of week. Replacement board will be here tuesday morning. 
Resistors were all the same, they are all shot, but I was able to read the bands.


----------



## Wirenuting (Sep 12, 2010)

farlsincharge said:


> It's for the AC in long term care. Supposed to get hotter at the beginning of week. Replacement board will be here tuesday morning.
> Resistors were all the same, they are all shot, but I was able to read the bands.


IMHO, I would not try a repair. I would wait for the new board.
If cooling is required then I would have the customer use spot coolers.. 

If your repair goes south before the new board arrives, who do you think their lawyers will be eyeing?


----------



## splatz (May 23, 2015)

I wouldn't fix this on a bet in a hundred years, I guarantee that properly motivated someone can get a replacement drive plus a spare within 24 hours on a Sunday if necessary. 

but 

could you solder in leads to a potentiometer and adjust that to the correct value?


----------



## micromind (Aug 11, 2007)

How about bypassing the VFD and running it across the lines using the greater as the controller? 

Of course, there'll be no O/L protection but in an emergency.......


----------



## farlsincharge (Dec 31, 2010)

micromind said:


> How about bypassing the VFD and running it across the lines using the greater as the controller?
> 
> Of course, there'll be no O/L protection but in an emergency.......


Tried that for a few minutes, crawled inside the air handler and spun the blower wheel like I was a contestant on the price is right. Started it across the line, belts howling, lights flickering. It hit full speed and I thought the blower assembly was going to come right out the side of the unit. Shut it down before something broke and came to the conclusion that the vfd must never ramp it to full speed.


----------



## gpop (May 14, 2018)

splatz said:


> I guarantee that properly motivated someone can get a replacement drive plus a spare within 24 hours on a Sunday if necessary.


Fedex has a number for emergency assistance on a delivery. 5pm florida time 400lb on a pallet pick up in California delivery to florida by 9am. No problem that will be $28,000 postage. 8.45am there's the fedex truck.


----------



## matt1124 (Aug 23, 2011)

splatz said:


> could you solder in leads to a potentiometer and adjust that to the correct value?


Heh heh heh

When I was in engineering school, we had to make filters, timers, etc with DIPP components. Them guys would do all the math and figure out what resistor they needed exactly, I just used guess and check methods with potentiometers and made adjustments as needed.

Of course, the math guys work at IBM making serious bank building super computers and I just got my 92 ford pickup driveable again for one of the guys to drive monday...


----------



## telsa (May 22, 2015)

Those figure to be terminating resistors.

Still, I just don't do board repairs. Period.


----------



## farlsincharge (Dec 31, 2010)

telsa said:


> Those figure to be terminating resistors.
> 
> Still, I just don't do board repairs. Period.


What is their purpose/why do they grenade during power fluctuations?


----------



## telsa (May 22, 2015)

They exist to absorb energy... to kill it.

When the energy to be dumped is way too high... they smoke.

Whenever you see a rack of resistors lined up in parallel, 16, 8 or 4 across, you're looking at 'dump resistors' aka terminal resistors. They are ten-a-penny in digital logical systems.


----------



## MDShunk (Jan 7, 2007)

Some drive - any drive - any brand, would be my preference over board level repair of a VFD. I never liked hitting myself in the face with a hammer much. Somebody (likely within a 40mi radius of you) likely had some drive in stock that would have done the trick. Worst case scenario- go to the industrial supply house and get new sized motor and jack shaft sheaves to run that blower slower across the line.


----------



## MikeFL (Apr 16, 2016)

Usually pull down to get the voltage to zero faster when indicated.


----------



## gpop (May 14, 2018)

Danfoss has a complete rebuild manual that gives you step by step guide and measurements on how to trouble shoot and repair based on each section of the drive. Now i would never attempt to repair a board but replacing a board or cap is not that big of a deal as long as you have the spares in stock. 

The OP is really screwed as he has no idea what the original program was on the drive (thankfully danfoss doesn't have many parameters) so getting the drive up to read them would be useful. (if the main board is toast the original parameters are gone).

While any drive will work but one thats designed for a AC unit would be the best idea as by default they are set to reduce the noise of the motor (vfd squeal). I know that most drives can have the pulse freq changed to quieten the motor but that requires a good understanding on vfd programming.

In a emergency situation i would go with anything that works. If this kind of work was my bread and butter i would have a spare drive in stock that i could rent until parts came in. 

i may be a little bias as i cut my teeth on danfoss (even had some trianing years ago) and i have repaired a few of them by replacing parts.


----------



## John Valdes (May 17, 2007)

Somebody has to have a brand new drive sitting on a shelf close by. Or if not close you can have it couriered to your place.
If you cannot get a drive on a Sunday, you are in quite the spot.


Who's the distributor? Do they have a 24 hour emergency number?
Have a motor shop in the area? They sell drives too.
You should be able to replace it. No matter the brand.


----------



## EJPHI (May 7, 2008)

Late to reply, you probably fixed this already. Best advice was to replace the drive.

Those resistors might have blown up because something else failed. Without
digging into the board circuitry to verify correct operation, you may not have much luck with just replacing the resistors.

Looking at the board, my guess is that these parallel resistors are forming a current shunt off the source of the TO-247 MOSFET that is close by. That MOSFET may also be blown. If that is the case, what caused the MOSFET to blow?

EJPHI


----------



## farlsincharge (Dec 31, 2010)

Power bump took out the mosfet. I changed it.

The board has been recieved and was replaced wednesday last week.

However that is not the whole story.
Against popular opinion I jumped the resistors and tried the board out monday morning. 
I did not connect it to the drive, just to the 600v supply. Hit the disconnect switch, heard a snap, and then a massive plume of electronic smoke. 
Satisfied my curiosity anyway. Worth a try.

Traced out the wiring harnesses and determined where I needed to apply 24v dc to operated the drive package. Found a low voltage lighting power supply large enough to do the job and got it running. Ran like that for two days until the parts arrived.


----------



## Rora (Jan 31, 2017)

41/30 = 1.36666..., assuming this is the real value of the resistor? It seems overly specific but it's necessary to achieve proper voltage division in respects to a network of a lot of other components. If you're desperate, you could achieve this with 3x 4.1 ohm resistors in parallel.


----------



## EJPHI (May 7, 2008)

Nice try. Sometimes things work out.

In the power supply business we have a saying:

"Hall of fame or ball of flame"

EJPHI


----------

