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MEP-005A Noise Reducing Capacitors?


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  #1  
Old 12-06-2018, 11:53:11 PM
krc002 krc002 is offline
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Default MEP-005A Noise Reducing Capacitors?

Hello All,

Its been a long time since i posted on here, it doesnt look like much has changed though and im happy to see the site has been doing well.

Anyway, does anyone here have experience with blown capacitors on the backside of the load connection board on an MEP-005A? I have put several hundred hours on my set and a few nights ago, the output breaker shut itself off and tripped the short circuit trouble light.

Sure enough, upon firing it back up i had a nice big blue arc and some sparks down by my feat and the main breaker opened up and the short circuit light came on. I then took the louver set off and found that two of what i believe to be capacitors had holes burnt through the side and were covered with that tell tale electrical scorch/smoke. They look like the condenser that was part of old distributor based ignition systems.

Im wondering if these are even needed, as none of the civilian units i have, have these on the output circuitry. Is this something needed for operation or could i remove all four of them? In looking through the manuals, it sounds like they are there to reduce noise and radio interference. Im not a ham radio operator, so if they are what i think they are, i doubt i really need them but am also wondering if these popping is a symptom of 40 year old capacitors, or of something more serious.

Can anyone share any insight here?

Please see the attached photo and thanks!

Ken
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  #2  
Old 12-07-2018, 12:15:41 AM
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Jim McIntyre Jim McIntyre is offline
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Default Re: MEP-005A Noise Reducing Capacitors?

These guys?



I'd not think twice about deleting them...

They probably never did do much anyway.
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Old 12-07-2018, 12:19:47 AM
Thaumaturge Thaumaturge is offline
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Default Re: MEP-005A Noise Reducing Capacitors?

I'd say they were just for noise suppression. Myself I'd replace them with 0.22uF 600v orange drop non-polar caps.
https://www.jameco.com/z/QXJ2J224KTP...C_2208930.html
Doc
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Old 12-07-2018, 12:50:20 AM
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Default Re: MEP-005A Noise Reducing Capacitors?

^ This application calls for a safety-rated Y cap. Unless you know that cap is safety-rated for line-to-ground, I'd say he's better off without it...
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Old 12-07-2018, 01:56:21 AM
Thaumaturge Thaumaturge is offline
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Default Re: MEP-005A Noise Reducing Capacitors?

These caps run to ground. If they short, they blow breaker (as existing caps did.) I see no danger at all replacing them with those suggested, assuming hot side leads are properly insulated.
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Old 12-08-2018, 12:53:04 AM
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Default Re: MEP-005A Noise Reducing Capacitors?

I've shepherded my share of products I've designed through through various safety compliance tests and certifications. I don't claim to be an expert, but here's a few things I've learned.
  1. Hooking these bypass capacitors from each of the genset 'hot' wires to the genset chassis is not necessarily the same as hooking them to "ground" because it's not know whether the genset chassis is actually "grounded" or whether there exists a neutral-to-ground bond. This is a potential problem because when the capacitor fails in a short, it's not known if enough fault current will flow to trip a breaker. (Maybe the caps should connect from line-to-neutral, but this configuration does nothing to reduce common-mode noise.)
  2. If a cap were to fail in a short and the chassis doesn't provide for a high current path, the breaker won't trip, and the chassis will be made hot. Obviously, this is bad.
  3. It is for this reason that safety-rated Y caps exist. They are designed and rated to fail as an open circuit. They are used for line-to-chassis bypassing.
  4. The Jameco caps in the above post are not marked as safety-rated Y caps.
  5. Adding any cap to this genset is an attempt to fix a problem that doesn't exist, as far as we know from what the OP describes. There is no noise problem that needs to be fixed.

Therefore, I recommend against adding caps, especially the Jameco ones. And, given the fact the original caps are blowing, they're doing more harm than good, and should be removed.
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Old 12-08-2018, 03:14:39 AM
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Default Re: MEP-005A Noise Reducing Capacitors?

Referring to your own diagram: L0 (neutral) bonded to ground at same point as low side C3, C4 & C5. MEP-005 is a 30KW generator. The leads on the Jameco caps are at best 18ga wire.... GUARANTEE cap will fail OPEN.
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Last edited by Thaumaturge; 12-08-2018 at 03:43:18 AM.
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Old 12-08-2018, 09:23:34 AM
krc002 krc002 is offline
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Default Re: MEP-005A Noise Reducing Capacitors?

Thank you all for the advice. I too am leaning towards just removing them.

I know enough to maybe be dangerous on electrical noise, so perhaps some information about the loads i run with the unit will help to put some minds at ease and give me a chance to learn a little more.

In my shop i have several large VFDs' (on the order of 20 hp) and a large inverter based Miller Electric DC welding power supply. im quite fond of all of those VFD's and that welder so my only real concern with deleting these capacitors deals with those devices with digital circuitry within. (Those devices already probably put a ton of noise back on the line anyway). But, am i putting those machines at extra risk by deleting those capacitors? Is this a concern? As discussed, im not worried about radio noise for things like ham radios, but what about line noise? Would these types of capacitors do anything to reduce that?

If there was risk here, id probably just call up an outfit like Delks army navy and see if they can pull capacitors off of one of their old machines to make sure they are a good match. They stiffed me pretty well on an injection pump several years ago though, so id probably avoid it if i can.

Thanks,
Ken
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Old 12-08-2018, 11:04:29 AM
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Default Re: MEP-005A Noise Reducing Capacitors?

Quote:
Originally Posted by Thaumaturge View Post
Referring to your own diagram: L0 (neutral) bonded to ground at same point as low side C3, C4 & C5. MEP-005 is a 30KW generator. The leads on the Jameco caps are at best 18ga wire.... GUARANTEE cap will fail OPEN.
Doc
Ha. I saw that too. I have little confidence in that wire being there, because why would they install C6, if they bypassed it with a wire? (I owned a MEP004, and saw numerous errors in the manuals for it...) The C6 bypass wire isn't visible in the OP's picture.

Quote:
Originally Posted by krc002 View Post
n my shop i have several large VFDs' (on the order of 20 hp) and a large inverter based Miller Electric DC welding power supply...
OK, that does make it more interesting. Were those loads present when the caps blew? (If so, that might be the cause of the caps blowing because, as you note, those loads can push a lot of high frequency noise onto the supply wires.)

Last edited by Jim McIntyre; 12-08-2018 at 12:18:32 PM.
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Old 12-08-2018, 02:08:39 PM
krc002 krc002 is offline
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Default Re: MEP-005A Noise Reducing Capacitors?

The night she went down, i was running 2/3rds of a 50kw Dayton shop heater to clean out the over the summer slobber/wet stack and for heat in the shop. So mostly resistive load, aside from the small motor inside the heater which would have been inductive.
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