Help with solid state relay switch!!

Hey guys, so I purchased a 100A solid state relay to use with a spdt switch to turn my board on and off.

After connecting it, there is a voltage difference (4v) over the relay when off and my switch illuminates. When I turn it on, this voltage difference is subtracted from my actual voltage so I get a lower voltage (eg 24-4 = 20v)

This is not good as my low voltage alarm goes off and my esc will throttle down as it thinks the cells are low.

How can I fix this? or is my relay borked?

Cheers!!

Huh? I'm not sure how this could happen, you will need to speak to the electronics ninja's on here but you can't have it wired properly in my opinion.

Can you attach a photo or diagram as to how you have it wired?

bandaro said:

Huh? I'm not sure how this could happen, you will need to speak to the electronics ninja's on here but you can't have it wired properly in my opinion.

Can you attach a photo or diagram as to how you have it wired?

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I have a slight diagram at the end of this post: http://tombrereton.com/diy-electric-skateboard-part-2-electronics/

Battery + to + output on ssr and + input. - ssr to load and switch led +. - battery to - switch and load.
It was working until I used the board for a few minutes. When I push the switch, the esc gets power and the switch led turns on. But now the led is on all the time, but really dim when the button isn't pressed in.

Can we have the specific model of the SSR? I am assuming you have a DC/DC SSR. There should be datasheets that can tell the electrical characteristics of the SSR and why you have 4 Volts voltage drop from 24 Volts to 20 Volts. I've looked at the diagram and the one thing I wonder is why the LED doesn't have a resistor to give the LED the correct amount of current? To me, this is interesting to use an SSR as a simple switch though I wish

chuttney1 said:

Can we have the specific model of the SSR? I am assuming you have a DC/DC SSR. There should be datasheets that can tell the electrical characteristics of the SSR and why you have 4 Volts voltage drop from 24 Volts to 20 Volts. I've looked at the diagram and the one thing I wonder is why the LED doesn't have a resistor to give the LED the correct amount of current? To me, this is interesting to use an SSR as a simple switch though I wish

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The led is built into the switch, which is this model: http://www.ebay.com.au/itm/331656498840?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

The relay is this model: http://www.ebay.com.au/itm/301828189006?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Basically, as the switch is only rated for 5A or so, and my motor is rated at 60A, i needed a relay to turn on power. Is there a better way to do this but still be able to use a nice switch?

thanks!

tommyb10 said:

Basically, as the switch is only rated for 5A or so, and my motor is rated at 60A, i needed a relay to turn on power. Is there a better way to do this but still be able to use a nice switch?

thanks!

Click to expand...

I'm also using an ssr with a LED switch similar to that, wired as normally open and it only lights up when switched on. I think this is a great way to do it, leaves it nice and clean on the outside, and high current internally. Your relay is much cheaper than the one I got, but it shouldn't be causing a voltage drop... when the switch is activated (and the ssr led is lit) is there any resistance between the primary supply points?

Regarding the resistor point mentioned above, this is not needed in your case as the switch you linked is 24v anyway. For others reference: My switch is 12v, and I'm also running a 24v system. So to take the 24v down to a safer 12v, I chucked a small resistor on the power wire leading to the switch, so it shares the voltage, thus giving me about 12v at the switch. I forget the band colours/resistance, and it's covered in shrink now, but I believe it was 500 odd (does 470 sound right?) Google can confirm.

bandaro said:

tommyb10 said:

Basically, as the switch is only rated for 5A or so, and my motor is rated at 60A, i needed a relay to turn on power. Is there a better way to do this but still be able to use a nice switch?

thanks!

Click to expand...

I'm also using an ssr with a LED switch similar to that, wired as normally open and it only lights up when switched on. I think this is a great way to do it, leaves it nice and clean on the outside, and high current internally. Your relay is much cheaper than the one I got, but it shouldn't be causing a voltage drop... when the switch is activated (and the ssr led is lit) is there any resistance between the primary supply points?

Regarding the resistor point mentioned above, this is not needed in your case as the switch you linked is 24v anyway. For others reference: My switch is 12v, and I'm also running a 24v system. So to take the 24v down to a safer 12v, I chucked a small resistor on the power wire leading to the switch, so it shares the voltage, thus giving me about 12v at the switch. I forget the band colours/resistance, and it's covered in shrink now, but I believe it was 500 odd (does 470 sound right?) Google can confirm.

Click to expand...

I removed the ssr and measured 308 ohms between the output connectors when ssr is not active, and 307 ohms when it is. That is with negative lead going to positive terminal and positive lead going to negative terminal. The other way around I got 554ohms unactive and 492ohms active. When I do have it in my circuit though it was once reading it as short circuit (which I think it should be) when active, but this seems to have changed?

Hi there

I cannot find a data sheet (well not in English) for the particular DC SSR (100A @ 60VDC) so can only go on presumptions here.
The relay would in all probability have a MOSFET (or a few in parallel) to carry theoutput current.
These components cannot be easily inspected by simply measuring resistance with a multimeter. There is no physical switch, only a chip which is allowing or restricting current flow.
The best way to check correct operation of the switch would be to use the multimeter in current mode, break the circuit and insert the meter to make the circuit again.
In the "off" state there should just be the leakage current which would be less than a milliamp. In the "on" state the full circuit current will obviously flow. In this state the voltage drop across the relay can be measured, from this the internal resistance of the relay can be calculated. If you are getting a voltage drop of 4V in the on state then the relay is total rubbish. Even with "normal" riding, let us presume a 20A draw, this would equate to a heat loss of 80W (P=V*I). May sound not to much but that is a lot of heat from about a square inch of metal, the relay would be getting very hot very quickly without a substantial heat sink.
Another thing, if, a I suspect, the relay has a MOSFET in the output then if the relay is connected with the polarity reversed then current would flow over the MOSFET body diode - irrespective of whether the relay was on or off.
At the end of the day I think a simple test, out of the present circuit, would provide the best information.
Measure currents and voltage drops with just the battery and a simple light bulb in the circuit. If you see more than a milliamp flowing in the off condition or still see the 4V voltage drop in the on condition then change the relay.

Personally I would not recommend the Fotek relays - not at all! (They have a pretty bad rep in the business)
SSRs from. Crydom, Opto22 or Celduc would be my recommendation.

If I can be any more help please just ask. I am no skate guru but SSRs are in my line of work.

WeeChumlee said:

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Wow! Thankyou, lots of valuable info! I will measure the current as you suggested and report back! Cheers!

WeeChumlee said:

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I tested the circuit again off the board. I did not measure any current at all when the relay want active, however I still measured a voltage over the inputs of 4v, when the relay wasnt active. When it was active, my output was only 8v from a 12v source.

I assume my relay is dead?

Cheers!

Hi tommyb10

Just to be 100% sure.
What were you using as a load when you took the relay out of circuit?
I take it you had a complete circuit, with the multimeter in current mode and in series, inserted?
From what I hear though I am pretty certain that the relay is dead.

WeeChumlee said:

Hi tommyb10

Just to be 100% sure.
What were you using as a load when you took the relay out of circuit?
I take it you had a complete circuit, with the multimeter in current mode and in series, inserted?
From what I hear though I am pretty certain that the relay is dead.

Click to expand...

I had a 12v lamp which was in series after the multimeter in current mode which was to the negative output of the relay. I think thats how it was supposed to be? I had to have my multimeter on 10A mode because the milliamp mode is broken on mine (think I short circuited and blew the fuse )

Did the lamp light up when you applied a voltage to the input terminals of the relay?
If it din't then the relay is just knackered.
If it did, and you measured a 4V drop across the output terminals, then the relay is just really really bad.
Either way I think the best would be to throw it away. Sorry about that.

WeeChumlee said:

Did the lamp light up when you applied a voltage to the input terminals of the relay?
If it din't then the relay is just knackered.
If it did, and you measured a 4V drop across the output terminals, then the relay is just really really bad.
Either way I think the best would be to throw it away. Sorry about that.

Click to expand...

Yeah it's stuffed ordering a new one, hopefully it's all good after that

Thanks for your help!!