MGB: Heater Blower Upgrade

Anyone upgrade their heater blower motor? Mine doesn't move much air through the box so it is hard to demist the windscreen. Was thinking of putting in an upgraded motor (12v generic) that would spin faster. How about a different design for the "squirrel cage" fan.
I haven't put a relay on the motor yet but will this w/e. Does a relay really make much difference?

BTW, working on a '63

The Chicago MG club has a nice write up on their website about this very thing

http://www.chicagolandmgclub.com/photos/b_heater/

Yes, I added a relay, in addition to cleaning and lubing the unit, it seems
to run better - and at least it takes the load of the switch.

tedjr

[quote=tedjr]
Yes, I added a relay, in addition to cleaning and lubing the unit, it seems
to run better - and at least it takes the load of the switch.

tedjr[/quote]

I did the same, I also put in a new heater matrix. The relay really helped, the motor spins much faster, the heat will me run out if I have it on full.

Wiz, I upgraded to a GM three speed blower and switch in my Midget, really does improve the output. A similar upgrade in a B heater is shown here http://www.mgexperience.net/phorum/read.php?1,519704

Biil

You beat me to it. I'm doing that one in my car. I also pulled the entire heater control. It looks like if will fit nicely in a modified center console.

BTW - both the motor and squirrel cage are available new at Rock Auto. Can't find the switch though.

[quote="Bill Young"]
Wiz, I upgraded to a GM three speed blower and switch in my Midget, really does improve the output. A similar upgrade in a B heater is shown here http://www.mgexperience.net/phorum/read.php?1,519704[/quote]

I'll look into that - it would certainly be nice in mid-winter.

[quote=lars49]
Biil

You beat me to it. I'm doing that one in my car. I also pulled the entire heater control. It looks like if will fit nicely in a modified center console.

BTW - both the motor and squirrel cage are available new at Rock Auto. Can't find the switch though.[/quote]

Larry, I need to update that post since a lot of the pics seem to be no longer on-line. Regarding the switch, I actually made this one from scratch using a spare fan switch and bezel, some "found" plastic, a stock 3-speed switch, model airplane glue and the Dremel.

Larry, I used the switch that came in the Camaro that I took my engine from and mounted just the rotary switch in the new dash. I used standard push/pull cables to control the air flap and heater valve. As far as adding a relay, the GM installation used a relay to carry the current in the high blower mode and ran the power through the resistors in the lower two speeds. I did use the original GM relay as well to keep the motor running as efficiently as possible. Adding a relay is definitely a good idea, takes the load off the 30 year old switches in the MG which probably need the help by now.

2 related questions on the switch

Rick - where did you get the switch - Mouser, DigiKey ??

Bill - what year Camaro ??

Regarding the relays, I've planned on doing it for a while.

It was an '87 Camaro that I took the switch from. I was building a custom dash for my car anyway, but to get the switch to mount with the knob flush with the dash surface I had to add a special bracket behind the dash to hold the switch about 1/4" to the rear. That might be a bit tricky fitting it into a standard dash, looks like Rick's idea might be a bit better.

Thinking about this, the blower on my GT isn't bad, it puts out plenty of air, what would be nice though is a slower speed, could I just add a second power circuit with a resistor and convert the fan to two speed?

Yes Wiz that would work. You'd need to figure out what size resistor you need with that motor to reach the desired fan speed. A double pole relay would take care of the switching very nicely. You can get high wattage wire wound reistors with an adjustable tap to start with, then once the desired speed is found meaure the resistance and convert to a fixed high wattage resistor and you're in business.

[quote="Bill Young"]
Yes Wiz that would work. You'd need to figure out what size resistor you need with that motor to reach the desired fan speed. A double pole relay would take care of the switching very nicely. You can get high wattage wire wound reistors with an adjustable tap to start with, then once the desired speed is found meaure the resistance and convert to a fixed high wattage resistor and you're in business.[/quote]

I'll have to see what I can do, I can probably use a spare dash light rheostat just to get a resistance measurement, it wouldn't take long to figure out the speed I want.

Wiz, I bet that rheostat glows bright red for a millisecond or so before it smokes if you try to run the fan through it. I don't think it would come close to handling the load. Worth a try I guess, but make sure it's not resting on something flamable or that might be damaged from the heat. The instrument rheostat is probably good for a 1/2 watt or so but you're going to need something that will carry around 120 watts or so. The fan is fused at around 10 amps and at 12 volts thats 120 watts of power. That's the reason the GM resistors are mounted in the air stream, to keep them cool.

[quote="Bill Young"]
Wiz, I bet that rheostat glows bright red for a millisecond or so before it smokes if you try to run the fan through it. I don't think it would come close to handling the load. Worth a try I guess, but make sure it's not resting on something flamable or that might be damaged from the heat. The instrument rheostat is probably good for a 1/2 watt or so but you're going to need something that will carry around 120 watts or so. The fan is fused at around 10 amps and at 12 volts thats 120 watts of power. That's the reason the GM resistors are mounted in the air stream, to keep them cool.[/quote]

I'll let you know. :)

I bought the resistor pack that Rick suggested in his earlier tutorial..Haven't installed it yet - getting the heater box out has been a royal PITA. I'll grab my ohm meter and measure the various bits and post them.

[quote=lars49]
I bought the resistor pack that Rick suggested in his earlier tutorial..Haven't installed it yet - getting the heater box out has been a royal PITA. I'll grab my ohm meter and measure the various bits and post them.[/quote]

That would be appreciated.

I bought the rotary switch from Vintage Air, but it's a standard 3-speed switch you can get pretty much anywhere. Wiz, what you're describing with a switch and resistor is basically the same thing as is done in the later MGs. In most of the installations I found - including the MGs - the resistor was integrated into the heater box somewhere in the air stream. My understanding is that this is done for cooling of the resistor itself.

Yes the resister is located within the heater box. I was surprised to find it there when I did over the heater system a few weeks ago. My question...is that what gives the slower speed to the 2-speed switch? by running the power through a resister to cut down the output to the fan motor?

[quote=Albert]
My question...is that what gives the slower speed to the 2-speed switch? by running the power through a resister to cut down the output to the fan motor?[/quote]

Yes that's how it works.

A more modern option is to use a 12 volt motor control to electronically vary the amount of voltage reaching the motor instead of converting a bunch of power to heat with a resistor to slow the motor down.

Down in this thread I put a few pics in of a motor control I used...
http://www.mgexperience.net/phorum/read.php?1,1157782

Hey Greg,

That was very interesting! I watched the video, too.

Or, to vary the TIME 12V make it to the motor. A very modern way to vary speed of a motor and keep, esssentially the same power outpur is to switch the power source on and off. More off means slower, more on means faster.
I like the Fiero motor option, BTW, looks like there are a lot of them out there. Thinking about a switch from the same-will it work?

I finally got new battteries installed in my analog VOM today and measured the resistor pack for the Fiero blower. Unfortunately the resistance is so low that my meter was showing zero ohms, even for the series connection of all 3 resistors. Maybe if I had a digital meter I could get the resistance, but a Fluke is just not in the budget at this time.

Greg, that's a nice solution. Looks like it uses a power transistor to vary the voltage to the motor by increasing or decreasing the voltage drop across the transisitor and placing the resulting energy in a heat sink. Sort of like a nice solid state variable resistor. ;) That's the real down side of most speed controls for DC motors, they usually control the voltage which reduces the power the motor is able to produce and thus reduces the rpm. Larry, the resistance is probably going to be down in the 1 to 5 ohm range for those as they can't be much different from the resistance in the motor windings and those are usually pretty low also. I get pretty good results with a $3 digital meter I bought at HF, I've compared it to my Fluke and other high quality meters here a the office and it's close enough for 99% of all the work I ever need to do with a meter. Cheap enough to carry in the car for emergencies as well. They go on sale regularly so wait a bit, they often go for less than $5. http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=90899