Heater Blower voltage drop

[steveg]

My fairly new Moss replacement heater blower reduces my voltage by a much greater amount than my bilge blower or headlights:
2000 rpms: Heater Blower on vs off. Denso alternator with built-in regulator.

With headlights and bilge blower on - it's still above 13 volts.

Would be interested to know what might cause this.

 

[andrewss]

It looks as though with headlights and bilge blower on you are drawing 2 volts. Size of the cable and length of the cable will determine the resistance. What's the spec on the blower ? If we assume that the lights and blower draw 2 amps then the resistance of the wire you're using has 1 ohm. To draw less current increase the gauge of the wire on the blower. As I doubt you will be using either the headlights or the blower while the engine is not running (and your alternator is keeping the battery charged while running) I don't see a problem with 13,5V..

 

[steveg]

It looks as though with headlights and bilge blower on you are drawing 2 volts. Size of the cable and length of the cable will determine the resistance. What's the spec on the blower ? If we assume that the lights and blower draw 2 amps then the resistance of the wire you're using has 1 ohm. To draw less current increase the gauge of the wire on the blower. As I doubt you will be using either the headlights or the blower while the engine is not running (and your alternator is keeping the battery charged while running) I don't see a problem with 13,5V..

The picture with the voltage drop is with the heater blower only running. I also have a bilge blower. With the bilge blower and headlights on, there is very little voltage drop. With the heater blower only on, there is that 1-volt drop.

If I increase the size of the wire to the heater blower or add in a relay, will that reduce the voltage drop?

 

[Keoke]

If I increase the size of the wire to the heater blower or add in a relay, will that reduce the voltage drop?

I think so steve :
If you premise that the replacement heater blower was built with larger sized wire.

Increasing the power feed wire size should reduce the voltage drop.

Similarly, rerouting the blower feed power with a shorter power feed cable and using a relay should reduce the voltage drop also.

 

[steveg]

If I increase the size of the wire to the heater blower or add in a relay, will that reduce the voltage drop?

I think so steve :
If you premise that the replacement heater blower was built with larger sized wire.

Increasing the power feed wire size should reduce the voltage drop.

Similarly, rerouting the blower feed power with a shorter power feed cable and using a relay should reduce the voltage drop also.

In the next few days, will experiment by running a temporary thick hot wire direct to the heater blower from the starter solenoid to see how that effects the voltage drop. Will follow up then.

 

[Bob_Spidell]

If the power wire to the blower is causing the drop the wire will get pretty warm (it would be acting like a resistor).

 

[John Turney]

Is the blower turning slowly? If so, the current draw will be much higher, and a ticker wire won't help. I assume the blower is wired from the 35-amp fuse. Where's the voltmeter connected?

 

[steveg]

Is the blower turning slowly? If so, the current draw will be much higher, and a ticker wire won't help. I assume the blower is wired from the 35-amp fuse. Where's the voltmeter connected?

The blower is the stock setup - not turning slowly. The green wire is the harness; black is the blower - the harness wire looks pretty thin.

 

[vette]

I don't have the pertinent info on the Heater motor here at my desk, but I do have some notes from when I wired my car and install individual fuses for the different circuits. My note on the one fuse box i installed says that I installed a 5 amp fuse to protect the circuit of the heater motor combined with the fuel gauge. It must be that the original layout had the heater motor and fuel gauge combined on the same feed wire that would have been why I did it that way. So I will assume that the gauge isn't going to draw much, lets say no more than 1 amp. then the heater more being the heavier load I will guess is going to draw maybe about 2.5 or 3 amps. Just guessing but surely less than 4 amps. I don't have the specs with me, but if you can read what the wattage is of the blower motor and divide it by 4 amps that would be the maximum voltage drop that the heater motor would use. Unless it gets into a locked rotor situation.