Will a 25amp SSR work??

Hey All
I have been contemplating the idea of building a simple control box to control an eHLT and possibly in the future control a heating element in the boil kettle as well. Right now I think I’m going to use the simple set up to have one PID with the temperature probe in the eHLT and possibly run the boil kettle off the manual mode in the future. I have a 60 Amp breaker I can utilize so I was wanting to run a 5500 watt element and possibly two in the future. So with that said I have noticed that a lot of people are utilizing a 40amp SSR could I get by with a 25 amp SSR for a 5500 watt element? Is there a such thing as putting two 25amp SSR in series to equal a 50amp SSR? I’m asking because I can get the 25amp SSR for free.
Thanks

Lamp24 said:

Hey All
I have been contemplating the idea of building a simple control box to control an eHLT and possibly in the future control a heating element in the boil kettle as well. Right now I think I’m going to use the simple set up to have one PID with the temperature probe in the eHLT and possibly run the boil kettle off the manual mode in the future. I have a 60 Amp breaker I can utilize so I was wanting to run a 5500 watt element and possibly two in the future. So with that said I have noticed that a lot of people are utilizing a 40amp SSR could I get by with a 25 amp SSR for a 5500 watt element? Is there a such thing as putting two 25amp SSR in series to equal a 50amp SSR? I’m asking because I can get the 25amp SSR for free.
Thanks

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Series... no. It doesn't work like that. Basically the way it works is that the SSR can only have 25A running through it... if you put things in series along a single wire the current HAS to be the same. So if you put two in series they would both have 25A running through them and you would generate more heat. Not exactly the goal. Will it be enough... lets do the math.

P = I * V ... so 5500W = I * 220V, so I = 25A. Which means it "should" be enough, but its damn close.

The other reason people use 40A or such is that 25A SSR running at 25A is less "efficient" than a 40A running at 25A.

Personally I'd take the 25A SSRs and use them for something else... or use a smaller element.

Also, the 40A run much cooler with that load draw.

Thanks for the reply guys

EFaden yea I did the simple calculation and noticed it was darn close so that is why I was curious if I wanted some opinions on using the 25amp SSR.

Could one PID run two heating elements at the same time?

I would say if you can get a 25 amp SSR for free do it! I understand that if you are about to make a purchase it's a no brainer to go with the 40amp but that does not mean you NEED it. I am building my control panel this week and I will be using a 25amp SSR for my 5500 watt elements. I see no issue as long as you make sure to keep the heat sink cool.

This is a diagram that PJ wrote up for me based off what I had from a rims system I had and parted out so I could build my current system. You cannot use both elements at once with one PID but you can switch between them.

semiconductors by name are semi-insulators. when a current is passed over an insulator, resistance causes it to heat up by some amount. since solid state relays are based on semiconductors instead of physical switches, they heat up under normal usage.

a 25 amp SSR means that the device will reach its maximum permissable operating temperature (given standard or reasonable cooling methods), under a load of 25 amps. if you were to upgrade the cooling considerably, or happened to live at the north pole, this same relay would be able to handle switching much more power.

however there is a balance where it would just be easier to buy a higher-rated relay to begin with, instead of spending lots of money on a fancy cooling soloution for a cheap lower-rated SSR.

If the SSR's are free, why can't you put 2 in parallel? Should be equivalent to 1 50 amp SSR.

A 5500W element draws 22.92A. (They are rated for 240V not 220V. At 220V they have a wattage rating of 5042W) A 25A SSR should be able to handle that IF it has a proper heat sink and air circulation over the heat sink to keep it within its temperature limits.

ChuckO said:

If the SSR's are free, why can't you put 2 in parallel? Should be equivalent to 1 50 amp SSR.

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Because you can not guarranty they will switch at exactly the same time. If one is slightly faster it will bear the brunt of all the current until the slower one switches. The same is true with unlatching also except the slower one will bear all the current until it unlatches. It is not a good idea.

Sawdustguy said:

Because you can not guarranty they will switch at exactly the same time. If one is slightly faster it will bear the brunt of all the current until the slower one switches. The same is true with unlatching also except the slower one will bear all the current until it unlatches. It is not a good idea.

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+1... SSRs were not designed to be run in parallel like that.

Sawdustguy said:

Because you can not guarranty they will switch at exactly the same time. If one is slightly faster it will bear the brunt of all the current until the slower one switches. The same is true with unlatching also except the slower one will bear all the current until it unlatches. It is not a good idea.

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Never thought about switching time. Are there any specs available for the cheap SSR's?

Thanks

P-J said:

A 5500W element draws 22.92A. (They are rated for 240V not 220V. At 220V they have a wattage rating of 5042W) A 25A SSR should be able to handle that IF it has a proper heat sink and air circulation over the heat sink to keep it within its temperature limits.

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Correction... a "5500W/240V" element running on 220V will only be 4622W and will draw 21A.

Walker said:

Correction... a "5500W/240V" element running on 220V will only be 4622W and will draw 21A.

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Absolutely. I blame my answer on getting old and stupid.

Thanks for making me think again.

ChuckO said:

Never thought about switching time. Are there any specs available for the cheap SSR's?

Thanks

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They are about 10 milliseconds or so. Just about right for one to see a problem.

Using the 25A SSR should be acceptable for a 21A inductive heating system "if" you ensure it operates somewhere around room temp.

SSRs current ratings are significantly derated as the temp rises. So use a decent heat sink and consider a muffin fan to move some air across it. Since these things are free you can try about anything to keep it from heating up. If it gets too warm you'll know it... it'll simply fail open and system heating will stop.

You can Google the brand and model of SSR and should be able to find the derating chart which will tell you exactly what your 25A device will do at different temps. Keep in mind these aren't precise limits but sort of a ball park of what you can expect.

I buy and build thermocontrollers for various uses at work and generally spend the money for the higher rated SSR and forget the heat sink and fan. A 50A SSR can get fairly hot at 25A and still hang in there where a 30A device probably wouldn't survive. This is a good strategy if the SSR doesn't get too hot in normal use. If I build a system that I know is going to push the SSR, then I break down and get the heat sink and fan.

Sudz said:

If it gets too warm you'll know it... it'll simply fail open and system heating will stop.

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They actually tend to fail close, not open. I had no ventilation in my box when I first built it and my SSR eventually failed like that after about 9 months or so (roughly 15 brews I would guess).

Strike water went right up and past the set-point and kept rising.

I now have two little 40mm fans installed to move air in and out.

I have 2 dual 25A Crydom SSRs in my toolbox, with no forced air. I do have a killer heat sink though (0.7 C/W).

I've run 50+ batches on this system without a problem. 5500W elements in BK and HLT. 30A GFCI breaker. I run my BK element at about 80% for a 13.5 gallon boil.

passedpawn said:

I have 2 dual 25A Crydom SSRs in my toolbox, with no forced air. I do have a killer heat sink though (0.7 C/W).

I've run 50+ batches on this system without a problem. 5500W elements in BK and HLT. 30A GFCI breaker. I run my BK element at about 80% for a 13.5 gallon boil.

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heatsink inside or outside the box?