Relay testing

[Bitsyncmaster]

FYI for you electrical guys.

I laid out a new fan relay circuit board (circuit change to prevent fault with open ground). So I decided to set up a high current test jig to decide if I should use 4 oz. copper instead of 2 oz. with the new circuit boards.

At 30 amps load current my fan relay rev B drops 0.064 volts across the power and load pins. That is 1.92 watts of heating.

Using the same test jig and installing a stock mechanical relay (rate marked as 30/40 amps) the drop is 0.120 volts. That is 3.6 watts of heating from the load. Add to that the heat produced by the coil current 2.45 watts and total heating is 6.05 watts. I wonder if all brands of relays dissipate that much heat at 30 amps. I know I've seen some marked at 50 amp ratings and think I've seen a 60 amp.

I think I may use 4 oz. copper when I place this next PCB order. It cost more since I have to order full production boards.

[Bitsyncmaster]

Some more testing.

Tyco 0-1432787-1
Voltage drop at 30 amps = 0.057 volts

Beuler BU-5083W-0000
Voltage drop at 30 amps = 0.056 volts

Tested that no name relay again
Voltage drop at 30 amps = 0.118 volts

So far it looks like you want a name brand relay for the high current circuits (fan relay or blower relays). Note that Beuler relay is marked 40/60 A. I think the Tyco is rated at 30 amp (not marked on case). These are all new relays so maybe with age the readings may get worse.

[Bitsyncmaster]

I tested the 70 amp rated relay I bought from Del City.

SONG CHUAN pn 897-1A-D1
Voltage drop at 30 amps is 0.043 volts.

I would expect about half of the voltage drop than the 30 amp relays. This one is less but not half. These do sound like minute voltage drops but when your current is very high they do produce quite a bit of heat.

[Exolis]

Neat. Have you considered using two 30 Amp Relays in Parallel? Typically vehicles nowadays with 2 Elec Radiator Fans uses 2 Relays in parallel, though I don't remember what the Relay ratings are, maybe 25-30A.

Otherwise for a 30A load, I would recommend 50A+ Continuous current, big relays like that don't have too much trouble withstanding a little bit of heat.

[Bitsyncmaster]

Well I placed an order for new circuit boards with 4 oz. copper. I had to buy 200 boards to get a decent price. Also had to use 370HR material which is higher heat and less thermal change then FR4. I also ordered better MOSFETs which just came out on the market. So these new relays should be rated to 70 amps. There are no super large terminals (used on the AUX) relays off the shelf. I've already dropped $1500 on this project so may not get those large terminals produced.

[Riley88]

This is awesome news as i am going to be buying some solid state relays from you very soon. Love what you do for this community!

[SS Spoiler]

Any luck on job prospects?

[Bitsyncmaster]

Any luck on job prospects?

Had one prospect but have not heard back for a few weeks. The company that bought us 18 months ago has let a few more people go. It is the age thing that makes getting a new job very hard to get. All of us over 60 still have no jobs. Suggest you all build your 401 K up as much as you can.

[tom kish vin. 4357]

Had one prospect but have not heard back for a few weeks. The company that bought us 18 months ago has let a few more people go. It is the age thing that makes getting a new job very hard to get. All of us over 60 still have no jobs. Suggest you all build your 401 K up as much as you can.

you got that right!!

[Bitsyncmaster]

Some more testing.

Tyco 0-1432787-1
Voltage drop at 30 amps = 0.057 volts

Beuler BU-5083W-0000
Voltage drop at 30 amps = 0.056 volts

Tested that no name relay again
Voltage drop at 30 amps = 0.118 volts

So far it looks like you want a name brand relay for the high current circuits (fan relay or blower relays). Note that Beuler relay is marked 40/60 A. I think the Tyco is rated at 30 amp (not marked on case). These are all new relays so maybe with age the readings may get worse.

I built one of the new relays that I ordered with 4 oz. copper. It also has the new MOSFETs which are 30% lower on resistance.

voltage drop at 30 amps = 0.032 volts.