68 replies to this topic

[bgd73]

I have been digging around a bit today and fixing them by yourself is going to be a hassle,

the resistors have to be huge and expensive to make sure they can take the heat, because they wil have to dissipate 40W, 80W and a whopping 120W heat to turn the motor at the correct RPM :-\

you could settle for something smaller, because they're actively cooled, but still, HUGE

I'm going to order a new resistor pack from the dealer, only 33 euro's

I made the mistake you are stating as well. It really is low watts. I have a 56ohm for the smallest one and it is only a 3 watts resistor- works better than oem by staying cooler, getting similar job done. I am going to go 3 watts for all of them if I have to. I am fairly certain ordering them can get it exact or very close to it. The big watts defy the resistance value, I am assuming in the resistor world, small watts to go with the algorithm is the output- not how much the other end can take. This still a guess on my part- I have narrowed it down to "whatever works."
I have to order some to complete this, will post results. If less than 1 ohm on a 200 ohm scale the ".5" for example is "of" 200, that is why I multiplied it, and the numbers really made sense after that. Less than 1 ohm resistor is not doing hardly anythjing at all- an ohm meter itself can have up to a .3 in just error, that is how sensitive that number is below 1.
It is almost an entire guess if it were'nt for the 56 ohm I just happened to have sitting around in the resistor block and functioning.

[DaveT]

If less than 1 ohm on a 200 ohm scale the ".5" for example is "of" 200, that is why I multiplied it,


an ohm meter itself can have up to a .3 in just error, that is how sensitive that number is below 1.

[top quote] - That is not how digital ohmeters work / read. The 200 ohm range means the highest value of resistance that can be displayed is 200 ohms (actually 199 if you want to be picky)

[bottom quote] - My readings are corrected for the meter leads. Fractional ohm resistors in series with a motor that draws around 10 Amps on full power are quite reasonable. The 4-1/2 digit meter I used can read hundreths of ohms on the 200 ohm scale. In other words it can display the diference between a 1.01 ohm and 1.02 ohm resitor. You do have to be careful about correcting for the leads and make very good connections.

[joostvdw]

[top quote] - That is not how digital ohmeters work / read. The 200 ohm range means the highest value of resistance that can be displayed is 200 ohms (actually 199 if you want to be picky)

[bottom quote] - My readings are corrected for the meter leads. Fractional ohm resistors in series with a motor that draws around 10 Amps on full power are quite reasonable. The 4-1/2 digit meter I used can read hundreths of ohms on the 200 ohm scale. In other words it can display the diference between a 1.01 ohm and 1.02 ohm resitor. You do have to be careful about correcting for the leads and make very good connections.

I totally agree, and that's exactly why it needs such low resistance, and why the resistors should sink those massive amounts of heat, because the motor pulls 13 amps!

and that's the reason subaru made the resistors out of coil wire, they can take the heat.

so bgd, if your tiny resistors work, they will only work for a short period of time and the motor will be turning at way less RPM than it should

[bgd73]

I totally agree, and that's exactly why it needs such low resistance, and why the resistors should sink those massive amounts of heat, because the motor pulls 13 amps!

and that's the reason subaru made the resistors out of coil wire, they can take the heat.

so bgd, if your tiny resistors work, they will only work for a short period of time and the motor will be turning at way less RPM than it should

The starter alone would suck down 3 amps tops. The soob isn't this big! A heater motor is free spinning in a closed environment, the draw is hardly anything.120 watts on a resistor is HUGE. My ohm meter is a cheap one. At 2m scale one of the resistors is reading .005. I really do have to do some extra math to get it correct. Less than 1 ohm on the block is going to allow me to straight wire it with no resistors at all.
I will verify with some resistors with known numbers, my meter is not normal to go to 200ohms, would get actual numbers on some, mine isn't getting actual numbers. low watts big ohms is my best guess. Again the 56ohm I have is working perfectly in the block

I just verified my ohm meter with a 151 ohm resistor. My meter read it as 148.3, so it is to say that the resistors on the block are doing hardly anyhting for resistance, just enough to get hot. I will be the jackass to straight wire it and call it good if the numbers I got are correct - under 1 ohm for all of them.

[DaveT]

We can't be talking about the same thing. I have measured the current draw on an actual blower from an EA82 / Loyale / GL wagon. It is over 10 Amps when directly connected to 12V (full speed on switch) I don't know how starters get into this, but they draw hundreds of amps while cranking an engine. I never had reason to measure that, but I do have the equipment.

Where are you getting 120 Watts on a resistor? None in the blower circuit would see close to that during normal operation.

[joostvdw]

We can't be talking about the same thing. I have measured the current draw on an actual blower from an EA82 / Loyale / GL wagon. It is over 10 Amps when directly connected to 12V (full speed on switch) I don't know how starters get into this, but they draw hundreds of amps while cranking an engine. I never had reason to measure that, but I do have the equipment.

Where are you getting 120 Watts on a resistor? None in the blower circuit would see close to that during normal operation.

the 120watts figure comes from me

since I couldn't measure the resistor coils I did some math, if you want to cut up the 12V into 4 speeds, you will need 3 resistors, one sinking 3V, one sinking 6V and one sinking 9V, if you calculate the resistance needed with the amps the motor is drawing, you get .25ohm, .45ohm and .675ohm, then if you multiply the Voltage going over the resistor and the Amps going through them, you get 120W for the biggest resistor and 20W for the smallest.

maybe my calculations are wrong? or maybe you misunderstood? my electrical skills are a bit rusty :-p

[joostvdw]

sorry, dubble post, look over there ^^

[DaveT]

I pulled a spare blower, harness & switch from my "stock pile".

Hooked them up. Partially blocked the blower output to simulate the ductwork. This matters a LOT. The lower backpressure on this type of blower, the higher the load is on the motor. Supplied 12V to the harness. Measured V & A.

Speed Motor V Motor A Resistor Res V Res Power
High : 12V 16A 0 -- --
Med : 6.6V 9.5A .46 5.4V 50W in the .46
Med : 4.7V 6A .46+.6 7.3V 44W total, 22W in the .6
Low : 3.5V 4A .46+.6+1 8.5V 34W total, 16W in the 1

Motor V = Volts across motor.
Motor A = Amps through motor and selected resistors.
Resistor = ohms and chosen resistors by the speed switch.
Res V = Volts across the string of selected resistors.
Res power = total power and power for the individual resistor that makes the tap for the selected speed.

It looks like the 3rd resistor is a made by me replacement, slightly lower resistance than a stock one, so the low speed would be lower RPM, lower motor V, etc.

[beataru]

Hey... anyone know how to safely make my fan run faster???

[bgd73]

Hey... anyone know how to safely make my fan run faster???

Just had time to play with this, this rainy day.
I was thinkin radio shack and 2 dollars ought to get this going.

• the big resistor seems to last forever, I have even banged the resistor block around - left it alone.
• the middle resistor gave me a .5 -.8 reading
• the small resistor is plagued at a steady .3

this is what I did:
the smallest resistor - straight wired bare copper 12 guage, .1 ohm- never to get hot again.
the middle resistor got some experimentation. I had a 10 ohm, threw that in and tried it. One was super slow, 2 a little faster than super slow, air barely moving.3 and 4 still a blast. I took remnants of the #1 tiny strand and paralleled it in the middle with the 10 to cut the 10ohm in half (5.25). Sure enough it is quite noticably slower than "3" and "4". So I am thinking 7 -8 ohm, tiny watt resistor is going to be exactly what I want, but for now I am content with 1 and 2 being similar (still different- just not much notice), and slower than "3".
The only resistor to plague it now will be middle one, and that is simple enough. A big watt resistor, again, defies the ohm reading for reasons I don't understand. The same ohm resistor in small watts, normal size, actually does something. I am guessing that 7 ohm would be perfect in "tiny" watts, .5 - 2 watt would hold it like oem.

[Prospeeder]

lol i went and got a resistor from an old wagon at the yard with moss growing in it and missing windshield and doors, lol. it works fine.

[Cougar]

Just had time to play with this, this rainy day.
I was thinkin radio shack and 2 dollars ought to get this going.

• the big resistor seems to last forever, I have even banged the resistor block around - left it alone.
• the middle resistor gave me a .5 -.8 reading
• the small resistor is plagued at a steady .3

this is what I did:
the smallest resistor - straight wired bare copper 12 guage, .1 ohm- never to get hot again.
the middle resistor got some experimentation. I had a 10 ohm, threw that in and tried it. One was super slow, 2 a little faster than super slow, air barely moving.3 and 4 still a blast. I took remnants of the #1 tiny strand and paralleled it in the middle with the 10 to cut the 10ohm in half (5.25). Sure enough it is quite noticably slower than "3" and "4". So I am thinking 7 -8 ohm, tiny watt resistor is going to be exactly what I want, but for now I am content with 1 and 2 being similar (still different- just not much notice), and slower than "3".
The only resistor to plague it now will be middle one, and that is simple enough. A big watt resistor, again, defies the ohm reading for reasons I don't understand. The same ohm resistor in small watts, normal size, actually does something. I am guessing that 7 ohm would be perfect in "tiny" watts, .5 - 2 watt would hold it like oem.

To BGD73:

I think you are having a little trouble in understanding how your meter works and understanding Ohm's Law. The resistance and power rating numbers that DaveT gave earlier make more sense to me. Placing a resistance of more than 2 ohms into the circuit will cause the motor to run too slow.

Above, you stated that a piece of 12ga. wire is .1 ohms. This may be what your meter said but that is not correct. The real value is more like .001 ohms. This is why the wire didn't get hot. There is virtually no voltage drop across the wire to cause any heat. The copper wire isn't a resistor but a piece of nicrome wire is.

In your post #54 you stated that you read .005 ohms using the 2m scale. If you mean the 2Megohm scale, you are using the wrong scale to measure a small resistance. You need to use the 200 ohm scale for that. 2 Megohms is 2 million ohms. That isn't a open circuit, but for power situations you can consider it to be one.

I hope that helps clear up some things for you.

[robm]

Wow, I love DaveT's post. Nothing like actually dropping those cannonballs...

Now, what we need is a good PWM circuit that can replace all those resistors, and get infinite adjustment to boot, with minimal losses. Having the motor data makes it easier.

[beataru]

Wow, I love DaveT's post. Nothing like actually dropping those cannonballs...

Now, what we need is a good PWM circuit that can replace all those resistors, and get infinite adjustment to boot, with minimal losses. Having the motor data makes it easier.

YESSS I just got done driving home from my brothers house... and its cool when you go 50 with the Sroof and all the windows down... that little fan didnt cut it!!!

[robm]

Sorry. The PWM circuit I have in mind can only go 0-100%, not 0 - 150%. Which would not be good for the motor, either!

There might not be that much more heat left in the core to remove. More air, same heat from the heater core, will give you more air that is not as warm. We can probably guess the engineers at FHI got the numbers pretty close, anyway.

Why not roll up the windows?

I agree with the sunroof open, it helps dry out the car. But sunroof and full blast on the fan should keep you reasonably comfie, if dressed for the weather outside.

[DaveT]

Sorry. The PWM circuit I have in mind can only go 0-100%, not 0 - 150%. Which would not be good for the motor, either!

The PWM I have (& found the unit) is near 0 to 100%. A buck - boost converter could do the 10-150%, but like you said, shorten the life of the blower. And be a lot of work to design. It might not move much more air through the ducts, that would need to be tested first. I am working on re-creating the schematic for my existing controller. I could design a PCB....

[beataru]

I am open to replacing it with another different make (sacrelig ) blower motor... so any ideas??? I know the 04 tacoma has a motor like no other!!!

[DaveT]

I am thinking a key thing to increase the airflow - through the existing air handing system - is the static pressure at the output of the blower. At some point, as the static pressure rises, the blower just can't move air.

The design of the blades of the blower and the houseing will determine the staic pressure capability. If the bigger blower you mention is designed for the same static pressure as the existing one, (and the system backpressure is close to the maximum for the blowers) the bigger one won't move more air through the system..

So the first thing to test is the back pressure of the Subaru and any theoretical upgrade blower. A draft meter might work for this.

The bigger blower likely moves more air through the system in the bigger car because the whole system is bigger. So they need a bigger blower, and bigger motor to turn it. It all could work with the same static pressure as the subaru, but move more air.

Just some things to think about..

[beataru]

I know what your saying... Like an oil pump... thats one of the main reasons that engines that have been overevved extreemly high, the oilpump spins so fast it just spins... the oil doesnt moove at all... it all has to do with the passageways but mainly the design of the impeller, straight fins resist the freespin but create more hp loss, curved spin easier but, they have little effect when an engine spins at high rpm... Its also like a Turbocharger!!! Sorry, I get carried away..........