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Solution required for Relay burning issue

Mohan mrperfect

Mar 10, 2017
2
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Mar 10, 2017
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Hi All,

We have a product to control 3phase agriculture motor.

We have deployed many units in the field and during rainy seasons our product is getting damaged.

I have shown device connection diagram in attached image.

Damage is happening to Relay and all the semiconductor components on the board.

Relay contact tracks on the board is melting out and all the GND and VCC tracks on the board are damaging.

Images of the damaged boards are attached for reference.

You can find the data sheet of the relay in below link

https://voron.ua/files/pdf/relay/JQC-3F(T73).pdf

I suspect during thunder or lightning condition, very high voltage is striking the relay contacts.

Isolation between relay contact and coil is breaking down and this heavy voltage is passed to board through relay coil.

Please provide suggestions to solve this issue and protect relay from high voltage surges.
 

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Bluejets

Oct 5, 2014
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Voltage surges and lightning hits are two entirely different situations.
By the look of your boards, the latter is obvious.
Local supply authorities generally provide some lightning suppressors in some countries but any good lightning protection system is going to cost way in excess of a couple of boards.
Rural areas are prone to strikes and usually unavoidable.
 

bushtech

Sep 13, 2016
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Put up a well earthed lightning mast in the vicinity
 

shrtrnd

Jan 15, 2010
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Bluejets and bushtech have good observations. There may not be an easy solution to this problem, but if you're like me, you're willing to try anything about now. If this was me, I'd look into some heavy-duty MOV (metal oxide varistor) modules. They may help if the spikes aren't too large, and they may be able to take the hit in a large surge and be destroyed, limiting damage to your board. If this is lightning, there may not be much you can do to prevent disaster, but that's where I'd start to try to limit it.
 

shivakumar.r

Sep 20, 2011
1
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Sep 20, 2011
Messages
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Thanks for the Replay..

If this was me, I'd look into some heavy-duty MOV (metal oxide varistor) modules. They may help if the spikes aren't too large, and they may be able to take the hit in a large surge and be destroyed, limiting damage to your board
--> Please help with reference design or recommended parameters for MOV.
Where to put this MOV ? Across relay contacts ?
 

Minder

Apr 24, 2015
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Apr 24, 2015
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All pretty much the same advice as the other forums posted to!
M.
 

shrtrnd

Jan 15, 2010
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shivakumar.r, You should start a new thread with your particular application/problem and maybe somebody can offer you some advice.
NOTHING is going to stop a lightning strike. The only reason I suggested that Mohan mr perfect look into MOV's is because he said this problem occurs during his rainy season. I've been places where the monsoons last for months at a time. When that happens everything becomes damp and doesn't dry-out. Considering the possibility that dampness is adding to his problem (his board and all the outside circuitry), allowing current paths that shouldn't be there; if the surge he's seeing is not due to an actual extremely high-powered strike, as I said, the MOV may take the brunt of the hit and be destroyed, potentially limiting the damage he's presently experiencing. It's just something I'd at least TRY in his situation. His fuse unit and relays aren't acting fast enough to save his boards (something I would also do to the board inputs themselves if they aren't fused already). And an MOV may not work in his situation, but he's got a problem he's trying to solve, and that would be my first attempt to try to reduce the number of damaged boards he's seeing.
Something like bushtech's advice to install a lightning mast (we call 'em 'lightning rods' in the States) in the vicinity is another good attempt to deal with a problem like this.
In this situation, he's dealing with a lot of unikonwns, and unless somebody here comes up with a better idea, it's a trial-and-error guess as to the best way to try to save his boards.
 

Irv

Jun 7, 2017
112
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Jun 7, 2017
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Since this is a commercial product, you can afford to pay someone to help. I would start by asking a local radio station for the name of the person who maintains their transmission / tower equipment. In this area, it happens to be a retired amateur radio operator, who maintains the towers on top of a mountain. No doubt he has frequent problems with lightning, and knows what precautions to take.
 

HellasTechn

Apr 14, 2013
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Have you ever considered placeing the board inside an earthed metal box ? that might help protect the pcb.
 
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