SSR help

[couchsachraga]

I'm back at trying to set up an "opportunity" load again- I thought I had it, but I think the (cheap amazon) SSR is bad.

What I'm trying to do:  Use a NC SSR with Aux 2 on a Classic 200 to heat water (which I actually use for heat, not domestic in this case.  I can go on at length about that setup if there is interest - the short story is it an 80 gal hot water tank with 2 internal coils - the lower one is a loop from evacuated tube (solar thermal) with glycol in the loop.  It heats the tank when the sun shines....  The Upper loops is actually used as a "cooling" loop to cool the hot water tank back down - and runs a glycol baseboard loop.  The tank also has a fitting for an electric element, so I purchased this unit from Backwoods Solar:

http://www.backwoodssolar.com/products/diversion-loads/water-load-15v-30a-or-60a-30v-30a

currently set up as 30 amp load.

1kw of panels.

I'm assuming (never good..) I need a SSR with specs as follows:

40 amp DC or higher (might look for 75a to cover me if I end up using both loops? or does that not work with lower amperage?), up to 20v (realistic 16.4 max, even in equalize with cold temps)
INPUT of 0-15v, 200ma (if I'm understanding the AUX 2 output correctly...).

Am I on the right track, and would anyone be able to kindly point me where I might be able to purchase a particular unit well suited to this application, and from a reputable company?  From reading posts here I take it both Crydom and Teledyne are good brands?

Thank you all for any and all assistance you can provide!  I thought I had this set in the spring, turned it all off for the summer (no need of the extra heat!), and it's not getting warmer out now....

[boB]

Crydom SSR's are the most popular and work in most cases and Teledyne  may be a better product but
either one ~should~ work I would think.

I think you have your thinking correct on all of this.  SSRs will need way less than 200 mA so you are also
good there.  One thing that ~may~ be making things less reliable is the fast-ish PWM that comes out
of Aux 2.   If you could use Aux 1 that is slower than Aux 2, that may work more reliably.  It's just
that faster PWM is a bit more smooth if the load is something that needs to be regulated in voltage
or if you cannot supply fully-on power to the heating element from your battery.

Aux 1 can still turn on and off and on around 10 Hz, just not at 500 Hz or so like PWM 2 does.

boB

[couchsachraga]

Understood - I'll likely try Aux 2 first, mostly for the smoothing.  The wiring for the load is battery bank to a circuit breaker, then to a fuse panel, and one of the hot leads from the fuse panel to the SSR.

I'm still in the learning phase of SSR for certain.  Does this unit make sense?
http://www.crydom.com/en/Products/Catalog/1_dcl.pdf

(D1D40L - 0-100v, 40amp)

Thank you very much!

[boB]

Understood - I'll likely try Aux 2 first, mostly for the smoothing.  The wiring for the load is battery bank to a circuit breaker, then to a fuse panel, and one of the hot leads from the fuse panel to the SSR.

I'm still in the learning phase of SSR for certain.  Does this unit make sense?
http://www.crydom.com/en/Products/Catalog/1_dcl.pdf

(D1D40L - 0-100v, 40amp)

Thank you very much!

Yes, I would expect that SSR (40A,100V) to be the most rubust of their SSRs...

I would then look at the voltage across the SSR with an oscilloscope as it turns OFF.  This is due
to inductive kickback from the load if it is very inductive.  That can hurt them if they are too inductive.

You will also want to make sure they don't get too hot.  If the SSR is lasting for any length of time,
check its temperature (with a finger ?) just to get an idea.  If it's fairly cool or just warm to the touch,
after some time operating, then that's good at least.

[dgd]

If you are going to use this Crydom then its always  a good idea to mount it on a heatsink or at least a section of flat aluminium plate.
Also include a schottky diode to eliminate inductive feedback

dgd

[boB]

Right.  Always (almost always) use a heat-sink.

The only problem that might happen with too much inductance is that the external diode may also
get too hot and break.  The energy has to go somewhere.  You might even have to heat-sink
the diode.

High transient power dissipation can sometimes not show up so much as heat on the outside...
At least not as fast as the average dissipation.

But try first without too much of that in case the load happens to be fairly tame.

boB

[couchsachraga]

Thank you both for the clarification - and note on the diode (I do not currently have one in the setup... this is the first I've seen it is needed).  Oops!

I do have a decent sized heat sink already from my current non-working SSR.  Assuming (never safe, I now...) that it is a standard bolt pattern the Crydom should bolt right up to it.

What are the specifications for the diode I should pick up?

I've tentatively ordered one of these, and a spare (at 0.43 seemed to make sense), knowing I can using them for other electronics if it is not correct. 

http://www.mouser.com/Search/ProductDetail.aspx?R=SD12C-01FTGvirtualkey57610000virtualkey576-SD12C-01FTG


Once I get everything together I"m going to run it all past a friend of mine who is an electrician (and does solar installs among other things)....

[boB]

I was thinking about a diode more something along the lines of this one....

http://www.digikey.com/product-detail/en/APT75DQ60BG/APT75DQ60BG-ND/1494833

I'm not sure if that little one from Littelfuse will do any good ?  I expect that it might
just send a smoke signal but I might be wrong ?

In fact, you may not need any diode at all and there might have been some other kind of
problem the last time.  Just don't know without more R&D.

boB

[couchsachraga]

I suspect the problem last time may have been the SSR that cost 8.90 vs $80;)

[couchsachraga]

Well, I installed the Crydom SSR in question and it does at least appear to "open" and "close" correctly (both by using the feature to manually turn it "on" as well as Aux 2).

We had a good sunny day yesterday, brought he batteries back up to 100%.  What I did notice is that as Aux 2 "flashed" on the classic ("tickled" I think was the term previously used... though some of it was a pretty good "tickling") the voltage (measured with an "OK" but not RMS multimeter) from the output of the SSR to ground was running 1.8 to 1.9v.

When I manually switched it it was almost the same as the input side (I expect a little drop).

Is this likely due to my MM smoothing the "tickling" or is it possible the SSR isn't opening up all the way? (I'm used to using mechanical relays... so please bare with me!)

[boB]

Well, I installed the Crydom SSR in question and it does at least appear to "open" and "close" correctly (both by using the feature to manually turn it "on" as well as Aux 2).

We had a good sunny day yesterday, brought he batteries back up to 100%.  What I did notice is that as Aux 2 "flashed" on the classic ("tickled" I think was the term previously used... though some of it was a pretty good "tickling") the voltage (measured with an "OK" but not RMS multimeter) from the output of the SSR to ground was running 1.8 to 1.9v.

When I manually switched it it was almost the same as the input side (I expect a little drop).

Is this likely due to my MM smoothing the "tickling" or is it possible the SSR isn't opening up all the way? (I'm used to using mechanical relays... so please bare with me!)

The "tickling" you mention is the PWM output of Aux 2.  That is usually around 500 Hz and happens over about a 1 volt
window over the input or output voltage the Classic is looking at.

I like that term BTW !  It's proper when the LED is just kind of on a bit and off a bunch...  Just on the edge.
And either MM or the Local App won't change very often because the state of Aux 2 is sampled only briefly
but stays solid on that application until the next sample which could be only every 2 seconds if the Local App
or several minutes if My Midnite.

boB

[couchsachraga]

If I understand you correctly you are saying that the Midnite is performing as it is supposed to (which I expected as I've been thrilled with it so far)... and therefore the SSR is as well?  I'd just like to understand how the SSR works (in other words is it letting 2v through, or is it 12v (or rather 14.8 the other day) at such a rate my multimeter is smoothing the "0" and "14.8" values to "2"...?).  Someone I expected full voltage but less amperage, but I still have a lot to learn!

Thank you again!

[boB]

You are correct about the reading being "smoothed" by the PWM driving the SSR.  It is
the average of the current or voltage.

If you were to connect up a load to the 12 volts and it would draw, say, 20 amps from that 12 volts,
and then the PWM driving the SSR is on for half the time and off for the other half time, then the
current through that load would only be 10 amps, or half.  If the SSR is conducting for a quarter
of the time and off for 3/4 of the time, then you would measure about 5 amps of current.

Same with the measured voltage.  When the SSR is on for 1/2 the time, instead of measuring 12V DC
you should measure 6V DC.  1/4 time on, measure 3 volts DC, etc.

That's the magic of a semi-fast PWM signal turning the loads on and off.  It can appear to be smooth.

There can be problems and trade offs by doing this though some times.  Depending on the load being turned
on and off, the SSR can get hot of the PWM is TOO fast because it may heat up from inductive kick-back
energy from the load... Even if the load is supposedly "resistive".  And, it IS switching, although it is fast,
and smooth enough for most purposes, it might cause some flicker or noise.  But it is a pretty good
compromise so you don't have to have a solid state switch (the SSR) having to be continuously "partly"
on and partly off...  Otherwise the heat would be going into the SSR and you don't want to vary the dump
load in that manner if you can just make the load resistor heat up which is what its job is.

boB

[couchsachraga]

Thank you for taking the time to fully explain it - I appreciate it!

[couchsachraga]

Ok... more questions...  Things *seem* to be functioning correctly, but to be honest I expected more out of the setup.

Panels in full sun.

Classic in "Float" mode.

Aux 2 pulsing occasionally (and as noted a "smoothed" 1-1.9v reading).

Removing the fuse (so no power to the heating element) the controller decreases output by 2 amps (7.x to 5.x).

I had thought that the setting would allow me to use all the "extra" power coming in off the panels... but it doesn't seem to be doing that (or only 2 amps (at 14.x volts), which seems a bit small on my system (4x 270w panels).

Is this working as designed, should I be tweaking a setting or did I get the incorrect SSR?

Thank you for any words of wisdom!