Thread-topic: [TCML] **External Email** Re: DC motor fuse/rectifier issue
The electrolytic has too much impedance at higher frequencies, it does nothing. You need to shield the cables, including the ground, and ground the shield at both ends. At the driving end, you need an RLC filter that works from about 1/2 your coil freq to at least 10X the coil freq. I'd use ferrite beads, twist the leads all the way. Bond the shield to a metallic enclosure at the driving end, 360 deg low resistance bond as found on a 38999 type connector. Inside the enclosure, use two PI filters in series, at least. You can use a common mode filter from a computer power supply or something to help with common mode currents. Keep the positive and return isolated through the filters.
Regards, Bill
-----Original Message-----
From: Tesla <tesla-bounces@xxxxxxxxxx> On Behalf Of David Rieben
Sent: Wednesday, July 29, 2020 4:39 AM
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Subject: Re: [TCML] **External Email** Re: DC motor fuse/rectifier issue
Terry,
Yes, I’m pretty sure the case of my permanent magnet, treadmill duty DC motor is grounded to the mains ground. Also, Steve White brings up a point that I forgot to mention. I also use a small EMI line filter at the input leads to my motor as well as a 3900 ufd, 400 volt rated electrolytic cap in parallel with the input to the motor. I don’t think the cap really does that much, though, as the spinning inertial mass of the motor’s rotor most likely smoothes the ripple, and the presence of the cap didn’t prevent the instant smoking of my rectifier (nor did the EMI filter) when its case was grounded, either. Actually, I use appropriately sized EMI filters at several locations inside my master control panel, too. They do seem to help squelch the nasty, sensitive electronics killing kickback transients that are the natural consequence of the disruptive capacitive discharges associated with spark Tesla coil operation.
David
Sent from my iPhone
> On Jul 28, 2020, at 9:36 PM, Terry Oxandale <toxandale@xxxxxxxxxxxxx> wrote:
>
> Thanks Bill. I found three in my parts boxes, so I'm good.
> Terry
>
>
> On Tuesday, July 28, 2020, 08:47:45 PM CDT, William Noble <william_b_noble@xxxxxxx> wrote:
>
> If anyone needs them, I have a box of corcom filters from a satellite ground station that was decommissioned. Just send me an email.
>
> Regards, Bill
>
> -----Original Message-----
> From: Tesla <tesla-bounces@xxxxxxxxxx> On Behalf Of Steve White
> Sent: Tuesday, July 28, 2020 2:05 PM
> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> Subject: Re: [TCML] **External Email** Re: DC motor fuse/rectifier
> issue
>
> I just used the standard CORCOM EMI filters but I'm sure that other brands work equally well.
>
> Steve White
> Cedar Rapids, Iowa
>
> ----- Original Message -----
> From: "Terry Oxandale" <toxandale@xxxxxxxxxxxxx>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Tuesday, July 28, 2020 9:31:59 AM
> Subject: Re: [TCML] **External Email** Re: DC motor fuse/rectifier
> issue
>
> Thanks Steve. Do you have any suggestions on the filter? I was kinda headed in that direction anyway, but not sure what to look for.
> On Tuesday, July 28, 2020, 09:15:12 AM CDT, Steve White <steve.white1@xxxxxxxxx> wrote:
>
> I use a modified induction motor for synchronous operation using AC so its not exactly like your setup. I have done several things to protect the motor.
>
> 1. Independent ground for motor case and shield around power cable. Motor case and shield are tied together.
> 2. I added a line filter at the motor mounting point under the Tesla coil base.
> 3. I added another line filter on the motor power cable back at the control cabinet.
> 4. I added a varistor to the motor power cable at the control cabinet end.
>
> I've been operating this coil at 6.5 KVA for about 4 years now with no problem.
>
> Steve White
> Cedar Rapids, Iowa
>
> ----- Original Message -----
> From: "Terry Oxandale" <toxandale@xxxxxxxxxxxxx>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Tuesday, July 28, 2020 8:18:16 AM
> Subject: Re: [TCML] **External Email** Re: DC motor fuse/rectifier
> issue
>
> Thanks David...that exactly matches my observations, so yes, I did undo the center mounting bolt (allow the FWB to just hang there) just to see if that would help, but the problem, though less severe, continues to happen.
> I had also wondered about utilizing both legs (240) to power the motor (FWB) instead of just the single leg (120), This would require more careful use of the variac being the motor is only 90VDC rated.
> Terry
>
>
>
>
> On Monday, July 27, 2020, 08:30:40 PM CDT, David Rieben <drieben@xxxxxxx> wrote:
>
> Terry,
>
> My ARSG control assembly is set up pretty much the way you’ve described yours, and I had that very same issue with my coil when I grounded (mains, not RF) the outer metal casing of my FWB rectifier (also rated @ 1kv/50 amps). My FWB rectifier worked perfectly fine in this arrangement when only driving the motor, as long as the coil wasn’t ‘sparking’. However, once I turned the voltage feed variac to my transformer up enough to break down the spark gap and initiate sparks from the top load, the FWB rectifier shorted out almost immediately! I believe I let the magic smoke out of two or three of them in this manor! Once I replaced the blown out FWB rectifier with a fresh one AND removed the ground from its outer casing and just allowed it to ‘float’, it worked flawlessly throughout coil’s active sparking range of power throughput (and the voltage input range for the motor) and I had no more problems.
>
> David
>
> Sent from my iPhone
>
>> On Jul 27, 2020, at 6:54 PM, shaun <snoggle@xxxxxxxxxxxxxx> wrote:
>>
>> Does the motor case and variac share the same ground.
>>
>> -----Original Message-----
>> From: Tesla [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of Terry
>> Oxandale via Tesla
>> Sent: July 27, 2020 4:52 PM
>> To: 'Tesla Coil Mailing List'
>> Subject: Re: [TCML] **External Email** Re: DC motor fuse/rectifier
>> issue
>>
>> Blows only under higher powers, and could be related to ground
>> strikes or strike rail strikes. There is a lot going on when I bump
>> up the power, and the death of the rectifier or fuse has some
>> component of time delay before the obvious slowing of the rotor disc
>> is noticed. I do know that I've had ground and rail strikes that did
>> not result in this issue, so no definitive or observed issue that I can find that has an obvious direct correlation.
>>
>> Terry
>>
>> -----Original Message-----
>> From: Tesla <tesla-bounces@xxxxxxxxxx> On Behalf Of shaun
>> Sent: Monday, July 27, 2020 1:20 PM
>> To: 'Tesla Coil Mailing List' <tesla@xxxxxxxxxx>
>> Subject: **External Email** Re: [TCML] DC motor fuse/rectifier issue
>>
>> I use about the same setup with a 3hp dc motor and not blowing fuses,
>> the bridge does get warm. Can you just run the motor on the floor by itself.
>> Also does the fuse blow right away or ever time. Sounds like you have
>> an short in the wiring.
>>
>> -----Original Message-----
>> From: Tesla [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of Terry
>> Oxandale
>> Sent: July 27, 2020 1:51 PM
>> To: tesla@xxxxxxxxxx
>> Subject: [TCML] DC motor fuse/rectifier issue
>>
>>
>> I'm using a permanent magnet DC motor for my ARSG. Power is through a
>> variac, to a diode bridge, and then out to the motor under the coil.
>> The issue is that I can't keep the fuses protecting this circuit, nor
>> rectifier, intact. I use a 10 amp fuse at the control cabinet for
>> protection (just off the 120vac hot leg of a 240vac source), and the
>> DC supply cable for the motor is surrounded by grounded braided
>> copper. I have an ammeter to monitor the motor, which indicates
>> proper draw during runs (2-3 amps depending on speed), yet the cheap
>> bridge
>> (50 amp/1000 v) gets warm fast, and also does not endure an extended
>> run on the coil. A while back I created a filter of sort to smooth
>> the full-wave pulses (cap/reactor), but that made things worse, so
>> that was removed. I don't have a sufficient understanding of the
>> induced currents associated with these coils, and hoping someone here
>> can help. I have yet to determine if a failed bridge is the cause of
>> the fuse blowing, so I may insert some fuses at different points of
>> the circuit to find out. My assumption is the rectifier (very cheap
>> ebay
>> item) could be at fault, but there is a lot of knowledge I lack about
>> what impacts of these coils on surrounding/supporting circuits. Any
>> thoughts on what can do to resolve this?
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