Current going to Blower Motor can be higher than Headlights - why no relay mod?

[Gary Lewis]

My guess is that the high-side relay is probably twice as effective as the low-side relay. The high-side has pretty large wiring going into the cab from the starter relay to the ignition switch, then still large wire to the fuse box, and then smaller wire to the function switch and then to the motor. So while it goes twice as far as the low-side wiring it has lots of connections in it, and surely the connections have voltage drops in them.

Having measured the high-side voltage drop it now seems like I should measure the low-side drop. And I think I can do that by pulling the relay and jumpering 86 to 87. That will use the factory wiring, and I can measure from the motor's connector to the negative terminal of the battery for the voltage drop.

Headed to the shop......

Well, it looks like my guess was WRONG! There's .6 volt drop on the ground side with battery at 12.1 volts and the blower on High. So I fixed the smallest of the problems.

But, for some reason I haven't yet figured out I'm not getting the relay to come in to bring the blower to High. When I jumper 86 to 87 it does speed up the blower. So I have some diagnostics to do. Probably when I put the high-side relay in.

[Rusty_S85]

Well, it looks like my guess was WRONG! There's .6 volt drop on the ground side with battery at 12.1 volts and the blower on High. So I fixed the smallest of the problems.

But, for some reason I haven't yet figured out I'm not getting the relay to come in to bring the blower to High. When I jumper 86 to 87 it does speed up the blower. So I have some diagnostics to do. Probably when I put the high-side relay in.

When you are jumpering 86 to 87 are you still leaving the rest of the relay hooked up? if so the speed up is to be expected as you are adding double circuits to terminal 87. You have the power from the trigger side supplementing the battery side at terminal 87.

I bet if you take and jumper another wire to the battery terminal on the relay I bet you will see the same increase without jumpering 86 to 87.

[Gary Lewis]

When you are jumpering 86 to 87 are you still leaving the rest of the relay hooked up? if so the speed up is to be expected as you are adding double circuits to terminal 87. You have the power from the trigger side supplementing the battery side at terminal 87.

I bet if you take and jumper another wire to the battery terminal on the relay I bet you will see the same increase without jumpering 86 to 87.

I pulled the relay and made a short jumper with 1/4" male spades on each end. Plugged that into 86 & 86 and then measured the voltage drop from the motor's negative terminal to the battery's ground terminal.

[kramttocs]

I don't have a diode in the blower motor circuit. I used the diode that is in the PDB on the starter circuit.

Yes, my existing relay negates the resistor, but it only comes in when you switch to High.

My thinking on the power side is to put it on the left side of your drawing, and that is probably what you mean by a "hot" relay. It would provide all the power to the motor, regardless of speed setting. That will probably increase the speed in all settings by some percentage, and I'd expect that to get essentially all of the 16% in High. But as the resistors come in and the current decreases there'd be less voltage drop with the factory approach so less and less increase in speed as you go down on the switch settings.

Yes, the relay on the + side is what I did earlier in this thread and made the videos of. That relay is simple to wire up as it just requires cutting and placing the relay in the Br/O or O wires depending if you do it before or after the blower motor connector. I didn't add it to the diagram but we should make a completed diagram with both relays when the dust settles.

Where did you cut in for your ground relay Gary? It can't be done right at the motor or else it would bypass the resistor so curious how you have it so that it only comes on when the switch is on High if not using the NC and NO relay contacts as I drew above.

[kramttocs]

If you look at my pictures you'll see that -at first- I had put the relay in the O/BK wire.

Using it to take the motor to ground with the relay closed -and- letting current flow through the resistor block with the relay open.

But I needed a rethink on that, so went and disassembled the upstream splice, put a butt connector where I had tapped it originally.

Ok, so you undid the splice. That works.

Really it all comes down to isolating the High circuit from the Lo/M1/M2/resistor circuit so they can be active on their own.

I should have done that in the drawing I posted since it is likely the way most will do it. I am always in the mindset of easily reverting to stock so I was deadheading one of the wires coming out of the splice and then running a new wire for the output of the resistor.

Ultimately the exact same though.

[Gary Lewis]

Yes, the relay on the + side is what I did earlier in this thread and made the videos of. That relay is simple to wire up as it just requires cutting and placing the relay in the Br/O or O wires depending if you do it before or after the blower motor connector. I didn't add it to the diagram but we should make a completed diagram with both relays when the dust settles.

Where did you cut in for your ground relay Gary? It can't be done right at the motor or else it would bypass the resistor so curious how you have it so that it only comes on when the switch is on High if not using the NC and NO relay contacts as I drew above.

Scott - This is at a high level how I think I did it on the ground relay, and how I want to do it on the power relay. The only thing the ground relay changes is High, but the power relay powers everything.

 

[ArdWrknTrk]

Scott - This is at a high level how I think I did it on the ground relay, and how I want to do it on the power relay. The only thing the ground relay changes is High, but the power relay powers everything.

Gary, you need to show source and sink in your relays.

So, I have one of the six in my tiny pdc powering the motor at all speeds and the (really nice) U-techcenter blower running the motor back to the 6Ga. ground shared with the power distribution center.

I don't have a way to compare but my windshield seems to clear quicker.

[kramttocs]

Scott - This is at a high level how I think I did it on the ground relay, and how I want to do it on the power relay. The only thing the ground relay changes is High, but the power relay powers everything.

Thanks! So you did it before the splice - that clears it up.

That is how I did the power relay and I think about the only way one would really want to.

But on the ground relay, people will have at least 3 locations for where they can tie in the relay depending on their preference and accessibility

Am I understanding your results though that the ground relay doesn't really add much to help the voltage drop?

[ArdWrknTrk]

Scott - This is at a high level how I think I did it on the ground relay, and how I want to do it on the power relay. The only thing the ground relay changes is High, but the power relay powers everything.

Function to power relay pull-in coil... to ground, hot from battery.

Ground relay: hot coil to ground through the speed switch, motor to battery ground (or some substantial ground near the motor.

[Gary Lewis]

Function to power relay pull-in coil... to ground, hot from battery.

Ground relay: hot coil to ground through the speed switch, motor to battery ground (or some substantial ground near the motor.

Yep, that's how I think I did the ground relay, and how I plan to do the power relay - with the exception that power will be from a fuse in the PDB and then from the battery.

As for providing source, sink, etc, we'll get official schematics when we conclude. But I was just answering Scott's question of where I put the ground relay and thought I might as well show where I want to put the power relay.