Solenoids & Relays - Flyback Protection

Solenoids & Relays - Flyback Protection

Postby apSlain on Mon, 26 Nov 2018 11:58 +0000

Hi all,

Just had a question for the electrically savvy out there about a topic I just learned/read about. I've just had a winch installed (Runva 11XP Premium) onto my 'Lux and am looking at upgrading some of the electrical components - stronger isolator, in-cab controls, etc.

I'm looking to replace the isolator with an isolator/solenoid/relay that I can activate/kill from within the cab. My first question - can anyone recommend an engine-bay suitable/weatherproof relay/solenoid capable of taking the ~430A draw? I have seen the IB500 recommended (reasonable price) and the Blue Sea ML-RBS (much higher price). Not much else outside those two.

Secondly, in looking at Amazon reviews for the IB500, I noticed a suggestion for a flyback diode to prevent voltage spikes after disconnect. Does anyone have experience with this? I'm using a solenoid to power my accessories fuse block and that's been sans-diode without issue but don't mind adding these in for protection though I'm very hazy on how you'd go about putting one.

  • Does the diode go on the load wires or activator wires?
  • Is the diode's gray band toward the positive or negative?
  • How do you size the right diode to the circuit? I've got one that's 80A and one that's 430A (if at max. load), or do you match the diode to the activator wires? Example: here's an eBay listing of a 150A solenoid including a 9A flyback diode.
Will use my Google-fu tonight but any pointers would be appreciated...cheers.
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Re: Solenoids & Relays - Flyback Protection

Postby martynvella on Tue, 27 Nov 2018 4:41 +0000

A 5 amp diode is usually enough as it does not carry load, the voltage and speed is important, most use a schotty diode for speed. It is used to absorb the transient voltate generated when the field collapses often 150 to 300 volts depending on the winding, but bugger all current. It is connected across the coil with the band towards positive as the spike is opposite polarity.
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Re: Solenoids & Relays - Flyback Protection

Postby apSlain on Mon, 03 Dec 2018 4:55 +0000

martynvella wrote:A 5 amp diode is usually enough as it does not carry load, the voltage and speed is important, most use a schotty diode for speed. It is used to absorb the transient voltate generated when the field collapses often 150 to 300 volts depending on the winding, but bugger all current. It is connected across the coil with the band towards positive as the spike is opposite polarity.

Thanks mate, much appreciated and matches everything I managed to find on the subject. I'll probably chuck this on my solenoids going forward.

Had to opt for the IB500 from the U.S. for the winch isolator/relay; couldn't find much else out there that was suitable.
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Re: Solenoids & Relays - Flyback Protection

Postby rjo89 on Mon, 03 Dec 2018 6:36 +0000

I don't know much about those huge isolators and relays, but I had in-cab controls on my old BT50. All I did was run trailer cable from the control box on the winch bar (only needed 4 cables though). Cut the little ground cable on the isolator, run one wire into the cab and connect it to the isolator switch, run another cable from the other side of the isolator switch back to the other side of the cut ground cable, then use the other two for the in and out switch (one for in, one for out).

Simple, and really really easy to wire up.
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Re: Solenoids & Relays - Flyback Protection

Postby apSlain on Tue, 04 Dec 2018 4:03 +0000

rjo89 wrote:I don't know much about those huge isolators and relays, but I had in-cab controls on my old BT50. All I did was run trailer cable from the control box on the winch bar (only needed 4 cables though). Cut the little ground cable on the isolator, run one wire into the cab and connect it to the isolator switch, run another cable from the other side of the isolator switch back to the other side of the cut ground cable, then use the other two for the in and out switch (one for in, one for out).

Simple, and really really easy to wire up.

Cheers for this. Yeah, I think it should be fairly simply to wire up - just getting the right spec. gear can be a hassle.

I also plan to re-locate the wireless transmitter inside the cab (piggybacking off the in-cab controls) as Runva doesn't rate it as waterproof...but won't be able to do all this until end of December due to shipping.
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