dc ssr wiring with classic

[bennyspoon]

hello everyone.

i have been experimenting with the waste not high function on my classic with an ac ssr on aux 1, works wonderfully.

when i try it with a dc ssr on aux 2 i am having some problems. i have a large resistive element connected that draws 30 amps and have used a 40 and 80 amp ssr. each time i have tried it the ssr stays on, even after the switching voltage is removed. 

i have the load wired to go through the relay, as in an automotive relay. in the picture,one wire goes to the load, the other wire that is removed went to the positive bus bar.

is this incorrect?

or do i need to incorporate a diode somewhere in this wiring? 

i have a crydom ssr waiting to go in, but want to get it right.

thanks,
ben.

[zoneblue]

Those ebay "Foteks" are rubbish. Place in the nearest trash can.

[ClassicCrazy]

How hot did it get when it had that load on it ?

Larry

[dgd]

Take a look at the topic SSR help

[kitestrings]

They really should be mounted on heat sinks.

[bennyspoon]

classic crazy- it didn't really have time, i enabled the output on the classic, then disabled it and it was stuck on.

kitestrings- they are on heatsinks and the fan above them was activated at the time. just not really visible due to the angle.

dgd- is the topic ssr or ssr help?

thanks.

[ClassicCrazy]

classic crazy- it didn't really have time, i enabled the output on the classic, then disabled it and it was stuck on.

kitestrings- they are on heatsinks and the fan above them was activated at the time. just not really visible due to the angle.

dgd- is the topic ssr or ssr help?

thanks.

There a jumper setting in the Classic that you need to set for aux - is that set to the proper setting to control your relay ?
Larry

[bennyspoon]

 Yes indeed, jumper is in the correct position.

I suspect it has to do with the diode i am lacking, and quite possibly the poor quality of the test ssr's that i used.

Of course i could be totally off the track too.

[kitestrings]

ben,

It looks like you are wired correctly, except that you should have a breaker or fuse.  Just to rule out the obvious - the relay basically is just a switch in this case closing between terminals 1(-) & 2 (+)whenever there is over ~3VDC applied to 3(+) and 4(-), so if you isolate the signal wires from the classic and apply a voltage (3- 1.5 volt cells will work) it should close the switch.  You can also manually turn the aux2 on/off with the signal wires off and make sure you have 12V, and the correct polarity.  I assume you have a DC load and are within the rating of the relay.

You didn't mention voltage, but at 24V your pulling 750 watts; 48V would be 1.5 kW, that's handling quite a bit of load.  It looks like you're mounted on a (AL) plate on the wall.  You may need fin tube and/or stand-offs form the wall for proper cooling and it should have heat-conductive grease between the surfaces.  Heat will eat these things.

I've had one fail recently - though it's worked well for years - on a water pre-heating set up like what your doing.  Unfortunately they usually fail closed (as do mechanical relays).  With SS they usually appear fine, but regardless of the LED indication just don't open.  I found my voltage a bit low one sunny day, and soon found a load on that circuit unless I turned the breaker off.

Good luck, ~ks

[SolarMusher]

Yes indeed, jumper is in the correct position.

I suspect it has to do with the diode i am lacking, and quite possibly the poor quality of the test ssr's that i used.

Of course i could be totally off the track too.

I've got the same problem with a brand new crydom mounted with... diode. To me it's may be a faulty ssr but you really need to start it carefully with your Aux in manual off or auto when off only. I finally had success with two used crydom (don't ask me why ) and switch it manually several times a week to discharge a bit deeper without troubles since two years.
A+
Erik

[kitestrings]

I believe a diode is recommended if it is an inductive load.  See: http://www.crydom.com/en/tech/tips/dc%20relays-technical%20guidelines.pdf

These are the ones we've been using:
http://www.futurlec.com/Relays/SSRDC200V40A.shtml

[kitestrings]

There also are derating curves for PWM, as in this datasheet 9pg3):
http://www.alliedelec.com/m/d/c380a8cb3fc32481a036c0f876f41695.pdf

[ClassicCrazy]

Thanks for the links - I have been learning a lot about these relays from reading that info.
Larry

[bennyspoon]

hey thanks for those links kitestrings, i hadn't considered the temperature derating- a good point.

i am at 48v. i will take a pic from another angle , they are on heatsinks, just not a good angle in that pic. i was a little impatient and left the breaker out.........foolish boy, tempting murphy!

once i install the diode i think we will be up and running.

thanks,
ben.

[kitestrings]

I just thought I'd shared some related information that I obtained recently on SSR's.  As I mentioned, we had one of two relays fail not long ago, and I was looking to replace it.  The original relay was no longer available, and I started communicating with a friendly sort, named Steve, at:
http://solidstaterelaystore.com/index.aspx

I had understood that a diode was required with inductive loads, but some of the vender information suggests that all loads are inductive to an extent.  In fact, I ask Steve this and this was his response:

    "Yes, even resistive loads have flyback from the wires. The entire wire length from the PSU/Source Output Capacitor, through the SRR, the Load and back to the PSU/Source is inductive. There are multiple approaches, but given this is a replacement part for an existing installation, the flyback protection should be in place. For insurance use a TVS20 (200V max. clamping voltage) across the output of a PE2040.
This simple/easy/effective.

    The TVS20 should not get hot. If it does, then whatever over-voltage protection was used, it is no longer working. IF the TVS20 is warn to hot, then it will do the job "as is". If the TVS20 is getting painfully hot, you will need a flyback diode, and possibly an additional capacitor to absorb flyback energy."

It appears they recommend the diode in all cases.  The MOV/voltage clamp in some, and even both in some.

~ks