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Thread: Solid state AUX relay

  1. #1
    Senior Member Bitsyncmaster's Avatar
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    Solid state AUX relay

    I've been running my headlight relay to replace the OEM AUX relays in the D. Those have been working fine but I had just glued the relay onto an aluminum angle to mount them and installed a standard relay socket to mate to them.

    Well that glue gave way so the relay has been laying in my relay compartment. So being very bored building products I decided to create the AUX relay. Not that the AUX relays need very high currents but the pins on the standard relay are really only manufacture rated to 25 amps. These "pins" are manufacture rated to 85 amps and I like the idea of using ring terminals.

    The nice thing with the AUX relays is I can make them larger than the standard 1.1 inch square size of the standard relays. I then 3D print a box to mount it. I use MOSFETs that have a typical 0.001 ohm on resistance. My Fan Relays (and headlight and blower) use two of those MOSFETs. I'm using 4 of those MOSFETs so that resistance should be 0.00025 ohms but I measured it with 5 amps (my 60 amp supply blew out) and got 0.00054 ohms.

    Again I'm not selling these yet because I can't keep up with orders on my old products. Building parts to sell just takes to much time and I'm running into parts shortages on some parts.
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    Dave M vin 03572
    http://dm-eng.weebly.com/

  2. #2
    Senior Member Citizen's Avatar
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    Quote Originally Posted by Bitsyncmaster View Post
    [snip]
    Again I'm not selling these yet because I can't keep up with orders on my old products. Building parts to sell just takes to much time and I'm running into parts shortages on some parts.
    If not for the parts shortages, it might be time to hire an employee to help.

    ...
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    Our cars are in the best operating condition they've ever been thanks to innovative people like yourself. Thanks, Dave.

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    Member mhanch's Avatar
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    Quote Originally Posted by iflights View Post
    Our cars are in the best operating condition they've ever been thanks to innovative people like yourself. Thanks, Dave.
    ^^^^^This!

  5. #5
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by Citizen View Post
    If not for the parts shortages, it might be time to hire an employee to help.

    ...
    It takes 2 to 3 hours of labor for my potted items each. I build 10 at a time. I really get sick of potting so I break away with something new to keep my interest. Anyway to pay someone to help at say $20 hour would really make the prices go way up.

    I built up the second AUX relay and this time put some extra solder on the legs of my MOSFETs and that resulting in a 0.00050 ohms on resistance.

    I put ring terminals on my harness for one relay. I started the 3D print for the second unit.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  6. #6
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    Dave, can your headlight relays be used in any application calling for a 5 terminal 30 amp relay?

  7. #7
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by CFI View Post
    Dave, can your headlight relays be used in any application calling for a 5 terminal 30 amp relay?
    The headlight and blower relays are 4 pin normally open "contacts" The difference is one drives the load to pin 30 and the other drives the load to pin to the opposite pin. They are all rated the same as the fan relay which is greater than 30 amps.

    The normal 5 terminal relays have that center pin normally closed to the load pin. That circuit is usually rated at less current than the normally open connection which is why you may see a relay rated at 30 amps and 10 amps. I've seen some state 60 amps but really the pins can not run that current without getting hot.

    My relays are only rated to 15 volts DC. They will switch on as low as 7 volts. You could not run them above 15 volts.
    Last edited by Bitsyncmaster; 10-09-2021 at 07:16 PM.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  8. #8
    Senior Member Bitsyncmaster's Avatar
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    Here are the two AUX relays installed. I mounted them further under the metal shelf to keep the wires out of way. Wish I could mount the RPM relay deeper but that has the mount fixed.

    The stock wiring is 10 AWG for the power and load for these relays.
    Attached Images
    Dave M vin 03572
    http://dm-eng.weebly.com/

  9. #9
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    Quote Originally Posted by Bitsyncmaster View Post
    It takes 2 to 3 hours of labor for my potted items each. I build 10 at a time. I really get sick of potting so I break away with something new to keep my interest. Anyway to pay someone to help at say $20 hour would really make the prices go way up.

    I built up the second AUX relay and this time put some extra solder on the legs of my MOSFETs and that resulting in a 0.00050 ohms on resistance.

    I put ring terminals on my harness for one relay. I started the 3D print for the second unit.
    Do you have to pot the items? What about custom making 3D printed plastic covers you can glue them into? If you have a 3D printer, you can print off quite a few of them at a time and then pop the solid state relays you make into them (with a bit of glue/epoxy) just how standard relays are built. Just a thought and may cut your time down and could also make it easier for repairs.

  10. #10
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by dmcman73 View Post
    Do you have to pot the items? What about custom making 3D printed plastic covers you can glue them into? If you have a 3D printer, you can print off quite a few of them at a time and then pop the solid state relays you make into them (with a bit of glue/epoxy) just how standard relays are built. Just a thought and may cut your time down and could also make it easier for repairs.
    I tried to 3D print a box for the relays and had no decent results. One thing is I would need to make the circuits a little smaller so the box can take up room to fit in 1.1" outside square. It would not be cost effective to 3D print many boxes. I would need to get them injection molded. I checked on the design for injection molding and that requires more careful layout of the model so the part ejects from the mold. My AUX relays are no problem since I make them 1.5" square and everything fits on one circuit board.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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