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Bad Contactor?

 
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Johnny240v




Joined: 04 May 2018
Posts: 11
Location: SF Bay Area


PostLink    Posted: Thu Dec 13, 2018 2:24 pm    Post subject: Bad Contactor? Reply with quote


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I’ve been running my panel (loosely a Kai clone (let’s say Kai inspired panel with some mods)) for a little over 2 years and recently replaced one of my contactors because it was getting very hot when I was running full power for a prolonged peroid of time, e.g. inital heating of my 3 tier system. Are contactors a common wear item, or did I make the mistake of buying an el cheapo Amazon part—Packard C230B 2 Pole 30 Amp Contactor, 120 Voltage Coil https://www.amazon.com/dp/B001KGSJ74/ref=as_li_ss_tl?ie=UTF8&linkCode=ll1&tag=theelectricbrewery-20&linkId=867325838ab6da5e38462846d1169695&language=en_US. I replaced it with a contactor that appeared to be higher quality Eaton/Cutler Hammer C25BNB230A Contactor, 2-Pole, 30 Amp, 120 VAC Coil Voltage https://www.amazon.com/dp/B00WN4UCIG/ref=as_li_ss_tl?ie=UTF8&linkCode=ll1&tag=theelectricbrewery-20&linkId=1d25f26b67c149e42c1d836956b061c8&language=en_US ? Or maybe I have a more serious system design problem? I haven’t done a full brew day on the new part, but I’m hoping this fixes the heat issue.

As a little background, the contactor I replaced powers up my whole panel. A single 120v switch activates the contactor and the contactor supplies 240v and 120v power to everything else (PID and other control circuitry at 120v and SSR and an SCR at 240v). I have 1 5500w elelment and use a 30amp GFIC circuit. I carefully poked around and found the trigger was getting the correct voltage and there was no buzzing to suggest the contactor was not fully closing. The output was right around where it should be, 240v. Does anyone know what the resistance should be across the coil? Maybe there was a short there. The power switch is fused at 1 amp and never blew—but that would require a decent short to do. The heat was only a problem when I was running the 5500w element continiously, but not when the panel was powered but not continiously heating.

I still have 2 of the old contactors in my system to alternatly power the PID SSR or the SCR. But I have not yet had problems with them.

Best, J240v
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kal
Forum Administrator



Joined: 12 Dec 2010
Posts: 11116
Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, Mild, Pliny the Younger, Belgian Dark Strong, Weizen, Russian Imperial Stout, Black Butte Porter


PostLink    Posted: Thu Dec 13, 2018 3:00 pm    Post subject: Reply with quote

While contactors can fail (just like any other part) they are not really 'consumable' parts that need replacing.

They may be slightly warm in use. They should not get very hot.

Heat is created when current flows through an area that is too small to handle the amount of current. This can happen:

(a) with a loose connection where only a few strands are making contact because the wire is not properly tightened/fastened, and/or
(b) a wire that is too small to handle the current is used, and/or
(c) when a properly sized wire is used but some of the copper strands were cut/trimmed to get it to fit (this should never be done), or
(d) a undersized part is used (ie: using a 30A contactor and passing 40A).

The first 3 cases effectively reduce the contact area meaning that more current flows through a smaller area which in turns creates more heat which can melt the insulation on wires and damage nearby components.

It could also be that you’re actually pulling too much current by using oversized heating elements. This would only be possible if an incorrectly sized breaker was installed in the electrical panel (larger than 30 or 50 amps, depending on your control panel size) as otherwise the breaker would pop if more than 30A or 50A was pulled. A 30A or 50A breaker should be used (sized for your control panel) per our control panel instructions.

Assumption is that that is a 30A panel since you're using 30A contactors.

I would look first to where all the heat is created. If a wire is melting, it's likely the closest spot to the bad connection.

I may also be a bad part, but that's rarer.

Johnny240v wrote:
The heat was only a problem when I was running the 5500w element continiously, but not when the panel was powered but not continiously heating.

Normal that things run harder with an element on. With a 5500W element on that contactor would be passing ~23A. With only the panel lights, PIDs, etc on the current draw is probably more like 0.1A.

If this is the first time you're replacing the contactor I would simply go ahead and use the replacement and see what happens. If that also gets very hot you have bigger issues (not a defective part).

Incidentally, we use oversized 50A contactors where 30A ones are required in our control panels. They're here: https://shop.theelectricbrewery.com/collections/ssrs-relays-contactors

Here's the exact one you'd use: https://shop.theelectricbrewery.com/collections/ssrs-relays-contactors/products/50a-250v-dpdt-contactor-120v-ac-coil

Kal

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Johnny240v




Joined: 04 May 2018
Posts: 11
Location: SF Bay Area


PostLink    Posted: Thu Dec 13, 2018 6:47 pm    Post subject: Reply with quote

Thanks Kai. In hindsight I should have bought the contactor from you since they are tried and true, overrated for the amps and the price is good.

My contactor was definitely too hot. It browned the insulation on the input side of the contactor.

The high amp wires are directly connected to the contactor via stripped wire (10g), so that should not be the problem. My first attempted fix was to tighten those contacts since loosening by heat cycling is a likely culprit. Oddly enough the side of the contactor that was the hottest / most toasted was the input voltage side, not the output side. There is one spade on the input side that got melted pretty good, but that just pulls low amp 120v power for the startup switch and contractor coil. I did suspect that spade contact and cut it off and recrimped a spade onto the wire and reconnected to the contector, with no success--same heat problem. Also the heat is a problem when I'm pulling 23 amps, not when the panel is on, but not heating, so the power used to close the startup contactor does not seem like the likely culprit.

On the output side I do have a spade connection for 120v control circuits and pumps, but that did not seem to be the issue either, and it did not get hot when I was just running the control circuits and pump.

Everything was sized properly: 10g wire (for the element), 30 amp contactor, 5500w / 23 amp element and 30 amp GFIC breaker. I also have 1 amp fuse for the startup circuit and a 5 amp fuse for the control / pump circuits.

I cannot say that I am certain that contactor is the issue, but I've run out of other theories right now. My best theory is that one of the contacts in the contactor became tarnished over time and wasn't making a good connection.

Best, J240V
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kal
Forum Administrator



Joined: 12 Dec 2010
Posts: 11116
Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, Mild, Pliny the Younger, Belgian Dark Strong, Weizen, Russian Imperial Stout, Black Butte Porter


PostLink    Posted: Thu Dec 13, 2018 8:39 pm    Post subject: Reply with quote

Johnny240v wrote:
I cannot say that I am certain that contactor is the issue, but I've run out of other theories right now. My best theory is that one of the contacts in the contactor became tarnished over time and wasn't making a good connection.

Yup, could be. Replace it and see what happens. If it turns out that it was actually a loose wire issue, removing and re-attaching the wires may fix that too. If any are tarnished make sure to cut & strip off clean copper. Make sure the wires are tight, make sure you don't cut off any of the copper strands either (effectively reducing the gauge)

Good luck!

Kal

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