Solid State Relay Specs.

[George7941]

I am considering using this relay
http://www.delcity.net/store/Hella-Solid-State-Relay/p_809798

I am looking for a relay with a "coil" (actuating) current not exceeding 5 ma. The Hella website is surprising short on information on this relay
http://www.hella.com/microsite-electronics/en/Solid-state-relay-130.html

I could use a reed relay but would like the "coil" current to be even lower. Anyone familiar with solid state relays?

 

[supton]

What is the goal? I don't know what the application is.

If you want really low current, I'd get a dirt common 2N2222 or 2N3904. Pick the proper base bias resistor, and for about 2mA of curent you should be able to run the typical 20-30A automotive relay (50-100mA coil current). Add a flyaback diode and you ought to have a very robust relay with low drive current.

You could go a step lower with a 2N7000, but I'm always a bit wary of FET gates in a noisy auto enviroment. I'd have a drain resistor, a series resistor and a zener to protect it. Although going this route could allow you to skip a relay altogether and just gate power using a FET.

What is the end goal?

 

[EdwardC]

I haven't used that specific SSR, but the ones I've used were very low current, essentially no current, with only a small initial inrush current (in the range of 10mA). If the inrush is too great, it might be worth throwing an inline resistor on the input.

 

[George7941]

Thanks, supton, for the suggestions. I might go that route if the solid state relay does not work out.

Application is on a truck ECM with what I think is a failing driver for the intake heater (similar to a glow plug) relay. It functions sporadically in the winter when it has to keep the relay engaged a lot more than it has to in the summer time. I checked the ECM pins and they look fine. I installed a manual switch on the dash to operate the heater but, since many different drivers use the truck, I would like the operation of the heater to be automatic.

I figure the tired driver circuit in the ECM should be able to handle 5 ma or less current

 

[supton]

Tomorrow I can try to draw up a schematic of what is in my head, and check on those auto relays. Ought to be able to keep it to Radioshack parts.

 

[qjohn]

The old Ford SSR part number F3LB-2C013-AA had about 10mA of current. Basically a 1.4K pull-up resistor to battery voltage on its input.

 

[George7941]

I have a Delco relay 212-366 from a truck which was scrapped in 2008.
http://www.amazon.com/ACDelco-212-366-Original-Equipment-Diesel/dp/B000C9ELLI

This relay only draws 3.5 ma but I cannot use it in my application because the ECM driver supplies ground to the Intake Heater relay in my application and this Delco relay is activated when supplied 12v to pin B.

 

[supton]

This miht work. Use 10k and skip the diode, as I'm assuming your module is not inductive. Should be just two parts from radioshack.

 

[George7941]

Ok, supton, you have convinced me to skip the commercially available relays and make my own. I will sort through my electronics parts cabinet and see what PNP transistors I have. I don't think I have a 2N3906 but I have some others that will do the job.

Radio Shack quit Canada fifteen/twenty years ago. I buy my electronics supplies from Newark/Element14 and they send it by parcel post.

 

[EdwardC]

If you have that Delco relay, you can use a transistor as an inverter and use it.

 

[George7941]

I could do that. I now have two choices.

BTW, supton, I think I still need the diode since the transistor will be switching the heater relay coil current and not switching the module as you implied.

The heater relay coil current is about 2 amps. Will the 10k resistor provide enough bias to supply 2 amps? If I have to go to 2.2k as the diagram says or even lower then the current climbs to 8ma or higher. In that case I should use the Delco relay since it only draws 3.5ma.

 

[George7941]

Are the terminals 30 and 87 isolated from 85 and 86 on SSRs in general and the Hella in particular? If not, the current through 85 could be a lot more than the actuating current when the relay switches on.

 

[supton]

2n3906 won't do 2A, but I thought your relay/module was going to carry the current? What is between the ecm and the heater?

 

[tom slick]

I don't know if this is helpful but Inpower makes very nice specialty SSRs. Their tech support is good also.

 

[George7941]

What is between the ECM and heater is a heavy duty relay, shaped like a starter solenoid and about that size, that switches the 90A current. This heavy duty relay coil takes 2A to operate.

The Delco relay is actually 2 relays in one, with a SSR driving a conventional (wound coil) heavy duty relay. With the Delco relay, I can eliminate the HD relay and let the Delco relay handle the 90A current.

If I use the Delco relay after inverting the signal, the current the module has to sink goes down from 2A to a few mA, whatever the inverting circuitry takes.

I will check out Inpower.