Solid state AUX relay

[Bitsyncmaster]

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.

[Citizen]

[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.

...

[iflights]

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

[mhanch]

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

^^^^^This!

[Bitsyncmaster]

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.

[CFI]

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

[Bitsyncmaster]

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.

[Bitsyncmaster]

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.

[dmcman73]

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.

[Bitsyncmaster]

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.

[Bitsyncmaster]

Just for your info. I'm measuring the conduction resistance so you can calculate the heating produced by any load current. I pump 5 amps through the load and measure the voltage drop in millivolts from the power pin to the load pin.

Well it looks like those 85 amp lugs I used on the AUX relay really make a big difference in resistance (voltage drop). I tested three pined relays with the same setup and got the following.

My solid state headlight relay resulted in 2.02 milli-ohms.

A standard TYCO 30 amp relay resulted in 13.4 milli-ohms.

A BEULER 40/60 amp relay resulted in 5.6 milli-ohms.

My AUX relay resulted in 0.50 milli-ohms.

So lets plug a 30 amp load onto each relay and compute the watts of heat it produces. This is not adding the heat produced by the coil power in standard relays which runs about 1 watt.

Headlight relay = 1.818 watts
TYCO relay = 12.06 watts
BEULER relay = 5.04 watts
My AUX relay = 0.45 watts

[Bitsyncmaster]

I got my 60 amp supply repaired and just ran the resistance check at 40 amps just to verify my old 5 amp check was correct. This also gives me more resolution.

My AUX relay resulted in 0.4935 milli-ohms.

So the resistance is resulting the same testing at 5 amps or higher amps.

[mhanch]

So dave - this makes me think - is there any reason to proactively replace the current AUX relays with something more modern in general? Would that perform any better in the system or is it not really needed?

[Bitsyncmaster]

So dave - this makes me think - is there any reason to proactively replace the current AUX relays with something more modern in general? Would that perform any better in the system or is it not really needed?

This is just to reduce some heat generated in the relay compartment. The OEM relays don't fail much.

[Bitsyncmaster]

I was doing some measurements of resistance on some circuit boards and I found the plug in relay contacts to be the most culprit to voltage drop (resistance). I was doing these test to decide how much a 4 oz copper saves compared to a 2 oz copper on my circuit board.

So my previous posted results were not very accurate with the standard relay values. The AUX relay was accurate since I measured the voltage drop right on the bolt terminals. These are the correct values with a 20.0 amp load. These voltage drops were measured right at the base of the relays terminal, not on the mating connector terminal. The resulting resistance is just the voltage drop divided by the current.

My solid state headlight relay resulted in 0.985 milli-ohms. My two MOSFETs = 0.50 milli-ohms so my circuit board is 0.485 milli-ohm.

A standard TYCO 30 amp relay resulted in 2.55 milli-ohms.

A BEULER 40/60 amp relay resulted in 2.54 milli-ohms.

This also shows why your relay pins can overheat. Make sure they are clean and tight.

[Bitsyncmaster]

I get bored building my products so to take a break, I ran a contact resistance test on a standard 70 amp aux relay. This is a new SONG CHUAN part number 897-1AH-D1 70 amp rated at 14 volts.

Interesting the cold start contacts dropped 0.0520 volts at 20 amps and the voltage dropped continually to 0.0293 volts where it settled at 12 minuets time. Since copper resistance increases when heated, I'm guessing the contacts are some alloy that resistance goes down when heated to cause that resistance drop.

So anyway that relays best contact resistance is 1.465 milli/ohm. So my solid state AUX is three times better.

Another interesting fact is that standard relay has bare copper battery and load pins but the control pins are normal tin plated. Maybe they found copper better for connector contacts.

I turned the control voltage off and on a few times after that test and voltage drop ran around 0.04 volts so it does look like the resistance drops due to heating.

Voltage was measured on the relay pins at the base of the relay so no connector drops affect my readings.

[DeloreanJapan]

Hi David Mckeen . I have some question about the Heavy duty relay

Recently I've been have a issue with stock Hella Heavy Duty Accessory Relay , I bought the modern Heavy duty relay from Delorean Go.

That I have never been use it until 2 years later now, recently I have a unknow issue of Car wont start . after checking the current and connection , I think its the

stock Silver Hella relay have acting abit wired . So naturally I just change 2 relay, but the car just wont start . with ignition key turn for 1 clicked , I can here the magnetic coil been pulled and making that Clicking sound from relay , but no radio and center console power . turn the ignition key for 2 clicked, relay will make will make sound ,But starter wont crank .

Maybe the relay I bought from Dgo was defective or the Spec of the relay was wrong ?
its a 14VDC 70AMP 4 pin relay . both relay internal Ω was around 50~60 Ω and seems normal .

In the end I just bang on the relay and fix the problem , in the end I switch both relay make the priority First for the ignition relay . since old one acting abit wired, so a dead radio can still make me drive to home .

Sorry its a Long artical . But Im very hoping looking forward when you have resourse to make the Solid state relay when you ready .

Best regards Peter

PS: Dont forget I have a RPM relay returned to your hand, ill order something in future , so you can return it with the new bought items.

[Bitsyncmaster]

The standard AUX relays are 70 amp rated units so I would guess you just got a defective replacement unit. Yes swapping the smaller control wires will swap what functions turn on with each key position. Good idea.

[Bitsyncmaster]

My parts vendors are always emailing me info on new components. Well this new MOSFET caught my eye. It specifies a typical on resistance of 0.0025 ohms, is automotive qualified and reasonable cost.

My last AUX relay used four MOSFETs rated at 0.01 ohms typical on resistance. So that result should equal 0.0025 ohms that new one MOSFET has.

This new FET is surface mount so I ordered 3 prototype circuit boards to do some testing and design changes. I did measure the voltage drop at the FET and it does indeed show 0.0025 ohms on resistance at 20 amps.

I never could find the larger relay pins used with the OEM 70 amp AUX relays. So I'm sticking with these nut and bolt pins which are rated at 80 amps. I guess I could manufacture the large OEM pins and bolt them on but that defeats the advantage of bolting ring terminal onto this relay. I will stick with my 3D printing the case for me but have not decided if I will be selling them since it would require you replace your harness pins with ring terminals.

Anyway I made circuit improvements and hope to eventually incorporate this MOSFET and the improvements into my FAN RELAY, BLOWER RELAY AND HEADLIGHT RELAY even though it is way overkill for those.

Battery voltage can now go to 30 volts for this relay if your driving a 30 volt load.
Control voltage threshold is 8.0 volts. Control voltage can also go to 30 volts but would add a little heating at higher voltage.
Control current is 1.31 ma. at 13.5 volts.
Current rating is 80 amps continuous.

I did not bother soldering the 80 amp terminals onto this prototype (they cost about $6 each). That will wait for production boards.

[The_J]

You're swamped because you have great products. Thank you for your support!
I have almost everying including the digital idle ecu which was a life saver as my original unit was failed.
I need to probably take a look and see what I am still missing from your collection and place another order

[Bitsyncmaster]

Well I decided to solder on the stud terminals. I wanted to measure if I need more copper. For this test board I just laid out 1 oz. copper on one side.

Testing with 50.0 amps.

MOSFET = 0.000202 ohms
Top of terminal to terminal = 0.000564 ohms
To first points where copper meets terminal = 0.000486 ohms.

So the copper will be 2 oz. on the production boards. Still deciding if I will lay more copper on other side. It would need some via's through the MOSFET pads.

[Helirich]

Dave I have a question that only you can answer. I have e-fans on a custom truck that fail quite often. They are Tyco brand. They look to be well made in Portugal. A friend of mine says the reason they are failing is the way in which I have them wired. The truck has a main power relay. When I turn that 500 amp relay on, it powers the main bus. From there, the power goes on to the fan relays. I have thermostat switches that trigger the fans on. I have it wired this way so when the main power is off, I know there is no drain on the battery.

So if I?m driving and the fans come on and then I stop. If I shut the motor down, the fans are still running because the water is still hot. If I turn the main power off, everything stops of course. My friend says you can shut the small relays off by the main power. He says I need to shut the relay ?triggers? off first, then I can shut the main power off. Would you agree?

[Bitsyncmaster]

Some cars the fans do continue to run after engine shut down. I would guess it is to cool the radiator. You would not want to keep the fans running if your sensors are not mounted at the radiator. There is no coolant flow after shut down.

Your relays should have a control pin and a ground. You should control the relay via one of those pins. Those are low current circuits so a switch or sensor can control it.


Dave I have a question that only you can answer. I have e-fans on a custom truck that fail quite often. They are Tyco brand. They look to be well made in Portugal. A friend of mine says the reason they are failing is the way in which I have them wired. The truck has a main power relay. When I turn that 500 amp relay on, it powers the main bus. From there, the power goes on to the fan relays. I have thermostat switches that trigger the fans on. I have it wired this way so when the main power is off, I know there is no drain on the battery.

So if I?m driving and the fans come on and then I stop. If I shut the motor down, the fans are still running because the water is still hot. If I turn the main power off, everything stops of course. My friend says you can shut the small relays off by the main power. He says I need to shut the relay ?triggers? off first, then I can shut the main power off. Would you agree?

[Helirich]

Some cars the fans do continue to run after engine shut down. I would guess it is to cool the radiator. You would not want to keep the fans running if your sensors are not mounted at the radiator. There is no coolant flow after shut down.

Your relays should have a control pin and a ground. You should control the relay via one of those pins. Those are low current circuits so a switch or sensor can control it.

What my friend says is you can?t cut the power to the trigger at the same time as the circuit. He called it ?flyback?. When I searched, it said most relays have protection from flyback.

[Bitsyncmaster]

What my friend says is you can?t cut the power to the trigger at the same time as the circuit. He called it ?flyback?. When I searched, it said most relays have protection from flyback.

When you switch off and inductive load, you do get a voltage spike. The relay is inductive (coil of wire) but it's spike is marginal. Yes some relays do put a diode inside them but they are very rare. The coil voltage spike has nothing to do with load voltage spike which is very large for electric fans.

[Helirich]

When you switch off and inductive load, you do get a voltage spike. The relay is inductive (coil of wire) but it's spike is marginal. Yes some relays do put a diode inside them but they are very rare. The coil voltage spike has nothing to do with load voltage spike which is very large for electric fans.

Thankyou

[jackb]

https://y.yarn.co/4e209d3c-f30c-4d93-aada-e5356217b728_text.gif

[Bitsyncmaster]

With the new MOSFET the board is very narrow. So I laid out a new 3D case and printed 4 of them at one time. The four takes 43.58 mL of resin and took 3 hours and 10 minuets to print. Resin printing has another requirement of washing in 99% IPA so that also adds to my cost.

[Bitsyncmaster]

I got the new circuit boards in and assembled 10 of them. The average on resistance is 0.000418 ohms. A little higher than I expected using 2 oz. copper on both sides of the board. I think my calculations did not account for the solder joint resistance. My old boards that used 4 MOSFETs was 0.00050 ohms so new units are a little better with less cost. The control current with 13.5 volts is 1.56 ma. which is much better then the old board which is 3.50 ma.

I did pot 4 of the new boards into my 3D printed cases. While doing that potting I was thinking that case could be designed with some clips to hold the boards in. However the resin I use is not very flexible so it would need another different resin.

Our AUX relays never fail so don't expect many owners will need these. My relays do produce much less heat (AUX relays are always on) and are silent when switching. I may run across different users that are in need of high current DC relays.

Anyway, I can sell the populated PCBs if someone wants to design there own case. You do need to replace your "push on" terminals on the power and load harness, to ring terminals. The control and ground terminals are the same as stock.

I have not calculated the price yet. The populated board should be less than $100 each.