# will this relay work for heater?



## Twilly (Jan 22, 2008)

A 1500 watt heater will draw about 11 amps at 144vdc... The relay tops out at 12 amps and that is with a heatsink...

I would look for something a little bigger, it might not handle the surge.


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## chamilun (Jun 17, 2008)

thats my concern. everyone is using a 10 amp relay for a device that pulls 12.5 amps at least.

hmmm


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## Twilly (Jan 22, 2008)

I used a battery isolation relay...


http://cgi.ebay.com/ebaymotors/Stin...m14QQhashZitem310091660841QQitemZ310091660841


It has worked great so far...


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## chamilun (Jun 17, 2008)

twilly,
that looks like it may be a *better* option than the solid state relays typically used. mostly because it is rated for high current and not high voltage. 



> Or use it to switch a very high current load with a small current. Use it for high powered air compressors, etc.


taken from a description on the website


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## Xringer (Oct 12, 2008)

Looks like a real nice relay. You don't see many rated for DC and high voltages..
Buy two of them and stack them. (parallel).
Heat sink them to some 1/4" aluminum plate.

Cheers,
Rich


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## rctous (Jun 18, 2008)

this waht Gav used and I got one that is wworking just fine as well

http://www.mouser.com/Search/Product...oXTBbJpA==

Brian


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## engineer_Bill (Jun 24, 2008)

Xringer said:


> Looks like a real nice relay. You don't see many rated for DC and high voltages..
> Buy two of them and stack them. (parallel).
> Heat sink them to some 1/4" aluminum plate.
> 
> ...


 Sink them to the plate (GOOD) stack two in parallel (BAD). Don't worry about the "SURGE" this is a heater not a motor. Unless it has tungsten elements, the surge on a a resistive element is very small. My experience is that these relays fail shorted, putting two in parallel doubles the risk. For safety put a snap switch in the circuit in case the solid state relay fails. Other than that you are on the right track.


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## Xringer (Oct 12, 2008)

engineer_Bill said:


> Sink them to the plate (GOOD) stack two in parallel (BAD). Don't worry about the "SURGE" this is a heater not a motor. Unless it has tungsten elements, the surge on a a resistive element is very small. My experience is that these relays fail shorted, putting two in parallel doubles the risk. For safety put a snap switch in the circuit in case the solid state relay fails. Other than that you are on the right track.


I've been using this kind of AC SS relays for years.








Most of the time, I was able to get the AC current rating that I needed.
But a few times, I've installed two 10 Amp models in parallel to get the
20 AC amps that I needed to switch. Never had a problem with them burning out. Very reliable devices.
I guess the DC versions must be using a FET instead of a SCRs.?.
Maybe that would make them more likely to burn out in parallel.?.


Speaking of "SURGE", I've got one of those neat little Ceramic space heaters, that has big surges a few seconds after it comes on (cold).
I have no idea why. It's just a basic heater with variable speed fan. 
No temperature control or anything..
But, it sure makes my EZ Kill-A-Watt meter beep and complain about over-current before it settles down to 900W..(at low fan).


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## elevatorguy (Jul 26, 2007)

I am using a smaller curtis contactor for the main and the other element I was going to use a Bosch 75A I found on ebay.

http://cgi.ebay.com/ebaymotors/New-...m14QQhashZitem140275256194QQitemZ140275256194

The PTC heaters don't have a surge but draw highest current when power is first applied, 15-20 amps then reduces as they heat.


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## Xringer (Oct 12, 2008)

elevatorguy said:


> I am using a smaller curtis contactor for the main and the other element I was going to use a Bosch 75A I found on ebay.
> 
> http://cgi.ebay.com/ebaymotors/New-...m14QQhashZitem140275256194QQitemZ140275256194
> 
> The PTC heaters don't have a surge but draw highest current when power is first applied, 15-20 amps then reduces as they heat.



So, that big increase in current (above normal) that I see when the heater comes on cold *can't be called a surge* for some reason.?.

Humm, maybe it's a PTMCP?? (positive temperature modulated current pulse)?


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## engineer_Bill (Jun 24, 2008)

Xringer said:


> So, that big increase in current (above normal) that I see when the heater comes on cold *can't be called a surge* for some reason.?.
> 
> Humm, maybe it's a PTMCP?? (positive temperature modulated current pulse)?


OK you can call it a "surge", my apologies. I still stand by my statement putting them in parallel doubles failure rate. 1 unless they are matched you will get a disproportionate amount of current through one of them, second if either fails you have a short or the other will carry all of the current, (and fail). I have an installed base of several hundred SSR's in devices I am responsible for. Yes; they are extremely reliable, I only change about 8-10 per year. Most of them shorted. I have a snap switch or other overtemp device monitoring any heaters driven by SSR's running to a main contactor. Also I have current monitoring that sounds an alarm if current is detected during the off cycle. I'm trying to put a damper on anyones project just pointing out that if your controlling a heating device designing a safety in case of failure is important. It is better to size the SSR rather than using two. They are available up to 100amps. If you are controlling a fan that is a motor and has a surge. If you are controlling the entire heater it will have temp control and a safety built in. In that case a mechanical relay will provide on/off capability with a high tolorance to starting surge and low probability of failing shorted. Be safe with heaters.


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## Xringer (Oct 12, 2008)

engineer_Bill said:


> OK you can call it a "surge", my apologies. I still stand by my statement putting them in parallel doubles failure rate. 1 unless they are matched you will get a disproportionate amount of current through one of them, second if either fails you have a short or the other will carry all of the current, (and fail). I have an installed base of several hundred SSR's in devices I am responsible for. Yes; they are extremely reliable, I only change about 8-10 per year. Most of them shorted. I have a snap switch or other overtemp device monitoring any heaters driven by SSR's running to a main contactor. Also I have current monitoring that sounds an alarm if current is detected during the off cycle. I'm trying to put a damper on anyones project just pointing out that if your controlling a heating device designing a safety in case of failure is important. It is better to size the SSR rather than using two. They are available up to 100amps. If you are controlling a fan that is a motor and has a surge. If you are controlling the entire heater it will have temp control and a safety built in. In that case a mechanical relay will provide on/off capability with a high tolorance to starting surge and low probability of failing shorted. Be safe with heaters.


I was just pulling your leg with the Surge stuff.  We all know *"The Surge"* can't be discussed here, since it's way off-topic. 

I don't think SSRs have to be matched for AC operation.. I never seen any failures, but I've never tried to measure current flow in each, to see if one was hogging the flow. 

Earlier, I looked around for a nice 20A DC SSR and found out that there are a LOT more AC SSRs for sale. What DC models I did find were priced extra high. Making me think, yeah, he should just try the one he picked..

I agree 100% on the need for some way to keep a failure from keeping the heater turned on all night.. 

And it seems to me that a simple fuse isn't going to be enough to stop a run-away heater. 

It wouldn't be too hard to wire up a DPDT heater switch (relay control) that would check for heater voltage on the element when the heater was switched* off*, and start up a warning beeper &/or flasher. 
(I'll bet someone has already done it)..

Take care


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## chamilun (Jun 17, 2008)

as entertaining as this is, could everyone please post what relay they are using to control their heater setup?


many thanks


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## Xringer (Oct 12, 2008)

chamilun said:


> as entertaining as this is, could everyone please post what relay they are using to control their heater setup?
> 
> 
> many thanks


Everybody left??

If you have to money, I would get this one.. 25 Amps 200VDC should do it.
http://www.grainger.com/Grainger/items/1EGK8

Bolt it down to a good heat sink and you can run your heater and get some extra heat from the heat sink too!


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## TelnetManta (Jun 5, 2008)

Rich,

I have a relay similar to this but it's a CRYDOM D4890 (90A at 280-480ACV). It is an SCR type relay. Do you think that this will work okay on a 144VDC pack to control a kettle type heater?

Sorry to hijack the thread but this thread has the best info about relays.


Ben in SC




Xringer said:


> I've been using this kind of AC SS relays for years.
> 
> 
> 
> ...


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## Xringer (Oct 12, 2008)

TelnetManta said:


> Rich,
> 
> I have a relay similar to this but it's a CRYDOM D4890 (90A at 280-480ACV). It is an SCR type relay. Do you think that this will work okay on a 144VDC pack to control a kettle type heater?
> 
> ...


The main thing I remember about SCRs is, *once ON, you can't turn them off. *
Remove the input control voltage and it STILL stays latched ON.
That's why the DC switches use power FETs. (Transistors).

So, if the 90Amp AC switch is set up like a side-by-side pair of SCRs,
then each one should be rated at 45 amps..?.
Therefore, you might be able to turn ON a space heater (drawing under 30ish?)..
But, to turn it OFF is another question. If the heater was reachable from
the drivers seat, you could just use it's built in switch.

Or, if the heater was down-line from the main power relay, it would go
off when the run key was turned off..
-------

SCRs are great for AC apps. Since AC goes up pos and back neg, passing thru ZERO volts.. At which point, the SCR can be turned off..


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## TelnetManta (Jun 5, 2008)

Hmm, well I don't know if I like that too much! This relay will be down stream from the main contactor but I don't want to have to shut the car down to turn off my heater. I thought you said you've been using these! 

Ben


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## Xringer (Oct 12, 2008)

TelnetManta said:


> Hmm, well I don't know if I like that too much! This relay will be down stream from the main contactor but I don't want to have to shut the car down to turn off my heater. I thought you said you've been using these!
> 
> Ben


I've used a lot of them. But all of them were in AC applications. 

I've seen some SS DC switches installed in equipment, but I've
never needed to build anything that used them.

Does the heater have a built-in off-on switch??


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## TelnetManta (Jun 5, 2008)

Nah, I'm using a water kettle type heater. It will be under the hood.


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## chamilun (Jun 17, 2008)

Ben,
Ive got mine all hooked up in the car but have not put any voltage to it yet. I plan to send the 144+ DC right to it, even though the plug is ac.

hopefully, it wont explode!


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## kugmo (Oct 31, 2008)

wow, I'll be researching on this, hopping to learn more...


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## Xringer (Oct 12, 2008)

chamilun said:


> Ben,
> Ive got mine all hooked up in the car but have not put any voltage to it yet. I plan to send the 144+ DC right to it, even though the plug is ac.
> 
> hopefully, it wont explode!


Which relay are you using? 
And did you put any heat sink compound on it before bolting it down?


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