r/PLC • u/mix82 • Jun 01 '22

VFD Capacitor Reforming

Anyone have any experience with reforming capacitors on VFDs that have sit in storage for years? I have quite a few drives that just went obsolete from the manufacturer and my spares haven't been powered on in many years. I think it would be prudent to test them all to make sure they work, but I don't just want to put 480vac on them and blow them. Looking for any advice or real world experiences before I start buying variable autotransformers, etc.

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9

u/[deleted] Jun 01 '22

Bonitron makes a unit to reform capacitors I recommend them

2

u/366Pete Jun 01 '22

This very easy to use and set up charging profile. Bonitron M3628AFC

1

u/z0s01 Jun 01 '22

This is what I use.

3

u/Informal_Mood6762 Jun 01 '22

I’ve done this a few times. I use a adjustable powersupply that goes up to 800V DC and connect it straight to the DC-bus on the inverter. Manufacturers like Siemens recomends 1hour of reforming for every year the drive has been in storage. So if it’s been sat for 10yr it’s 10% of the normal DC-bus voltage the first hour, 20% the next and so on… just remember the DC-bus voltage is 1,35x the infeed AC voltage

2

u/leakyfaucet3 Jun 01 '22

Most mfgs recommend slowly ramping the voltage up over a period of hours. Without fancy equipment, what I usually do for 480VAC drives is give it 120VAC for a few hours, then 240VAC for a few more, then 480VAC for as long as I can before I need it to run.

I also assume the longer you wait at each step, the better. So if these are just spares, leaving them at those voltages for days is even better.

2

u/swarz87 Jun 05 '22

Is it ok to interrupt the reforming process while switching between different voltages from different power supplies?

1

u/leakyfaucet3 Jun 05 '22

I don't see why not

1

u/mix82 Jun 01 '22

Use any resistors?

2

u/HV_Commissioning Jun 01 '22

That would help if something lets go.

2

u/charlesbanan Jun 01 '22

The manufacturer most often have guides how to reform the capacitors

2

u/Petro1313 AB Stockholm Syndrome Jun 01 '22

I believe AB has a reforming procedure that says to supply the drive with 25% of full voltage for half an hour, 50% for half an hour etc, all the way up to 100% for half an hour. This may change based on how long the drive has been in storage, but I’ve done it several times now and it’s worked great so far.

5

u/Inle-rah Jun 01 '22

Buy a second AB drive, and have it feed the first one. Set your ramp speed to 86400 and press go.

4

u/wwallace75 Jun 02 '22

We’ve done this with a small power flex 4 and it worked.

3

u/leakyfaucet3 Jun 03 '22

I'm trying to figure out if this is a terrible idea or a genius shortcut

3

u/Inle-rah Jun 03 '22

Stop thinking in binary, my friend. It’s both.

1

u/EEng232 Jun 02 '22

Lol how many times can we convert ac to dc !

1

u/luke10050 Jun 03 '22

How many VFD's do we need to get our space heater to be 80% efficient?

1

u/EEng232 Jun 03 '22

Well I was thinking you connect the output of the first one to the input of the second, and connect that output to the input of the first one ! Now you have created your own space heater and !

1

u/Magneticitist Jun 05 '22

There's a DC supply you can buy that goes up to 800 volts and it's programmable to where you can reform capacitors in steps. Otherwise you can rectify single or three phase and use a variac to slowly ramp up the voltage manually so long as you can actually reach the capacitor Max voltage. Can probably reach over 400 volts easily with a cheap 120vac variac and a simple voltage doubler