# Opinions on solid state high voltage DC relays?



## mora (Nov 11, 2009)

I have bought about 10 of those and have burned 5 of them already. Those fail closed and you cannot easily identify whether it is on or not.

External heatsink is absolute requirement. I'll still give them a shot and try forced ventilation to see if those last more than one hour of continous use. Temperature switch could also be wired in series with low voltage wiring and glued inside the heatsink to automatically switch off the relay in case the heatsink gets too hot. I'd like to switch my DC/DC on and off using SSR too.

I use two of them to switch heating elements on and off. I have two 1500W elements behind each of those, total 4 elements. At 96V and 10A load per relay they seem to last longer than I can watch. But when I upped voltage to 144V loads rose to 20A per relay. They got pretty hot even with external heatsink and one failed after one hour of continous use. There is no sound that indicates failure. Indicator led just shuts off and output fails shorted. There is no connection between 12V and HV side after failure though. I opened one and those have lots of other components inside.

Those could be fine if placed under the hood and well ventilated area. I'd also like to try how they behave when driven with 24V or more. Controlling them with 5V resulted similar failure as described above in less than 5 minutes. Same setup, 96V and 10A load.


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## Guest (Feb 9, 2012)

Was told they usually fail on but if you use your setup within the amperage rating and the inrush currents are under the rated amps then I am sure these are quite fine. But if you have inrush currents higher than the rated amps into the relay then you might cause it to fail over a short time and it will from what I have read, fail ON. Many air gap relays fail on too.

Pete


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## favguy (May 2, 2008)

Thanks guys, I must admit, I'm not liking them much so far!


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## tomofreno (Mar 3, 2009)

favguy said:


> Hi all,
> 
> I'd appreciate opinions on, or if anyone has any experience of this type of relay:
> 
> ...


 There seems to be a range of quality depending on manufacturer. I've been using a Magnecraft W6212DDX-1, 10A 2-32VDC input, 200VDC output for over two years now for connecting my DC/DC to the pack with the input wired through the ignition switch. I am not too concerned with failure in this case, as it would just leave my DC/DC connected with the key off, which I would see because my TBS gauge reads zero current with key off, and about 1.7A with key on and DC/DC and a small fan on. I use a 120VDC P&B DPDT mechanical relay I purchased from kta-ev for my heater. It looks like if you have higher pack voltage you need to go to a contactor for a mechanical switch, as I haven't found any higher voltage relays than the P&B. If you have the fuse for the heater where it is easily accessible I suppose you could always pull it if the ssr fails closed.


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## skooler (Mar 26, 2011)

Hi Favguy,

Not a direct answer but...

http://www.ebay.co.uk/itm/Kilovac-E...t=BI_Control_Systems_PLCs&hash=item43acaad0af

Cheers,

Mike


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## favguy (May 2, 2008)

Hi Mike,

Yeah, I'm familiar with the EV200, I've got one for the main contactor, just seems a bit overkill for the heater!

Do you think the ones in the link are real, coming from China & lots available slightly too cheap, maybe copies?


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## skooler (Mar 26, 2011)

favguy said:


> Hi Mike,
> 
> Yeah, I'm familiar with the EV200, I've got one for the main contactor, just seems a bit overkill for the heater!
> 
> Do you think the ones in the link are real, coming from China & lots available slightly too cheap, maybe copies?


Yep, I think its overkill too!

Again, I agree that it looks suspect. The sellers feedback looks reasonable though!

Cheers,

Mike


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## mk4gti (May 6, 2011)

On this subject, are typical automotive relays isolated? Meaning if I use ignition 12v to trigger HV, is there any chance of voltage crossing over? Even in failure mode (fused and all). Not thinking for heater but instrumentation.


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## Lee Hart (Oct 16, 2009)

mk4gti said:


> On this subject, are typical automotive relays isolated?


Automotive relays are isolated; but the isolation between coil and contacts is only built for 12v systems. The actual spec is something like 32vdc max.

If you compare an automotive relay with one that has 120vac UL/CSA/CE ratings, you'll find the 120vac relay has considerably more insulation between the coil and contacts.


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## favguy (May 2, 2008)

Having read Lee's other thread on the topic, I'll now be using 4 pole 220vac rated relays with the poles in series, (that was a great tip Lee ) and they are inexpensive to boot.


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