21 replies to this topic

[r2160]

I know this is a long shot, but has anybody measured the resistance of the coil inside the heater box for the slow speed of the fan?

 

I am in the process of rebuilding the heater box but the coil is broken

 

cheers

Glenn

 

[hanra]

If it's anything like an LH it's around 2-3 ohms from memory.

[Rockoz]

Are you thinking of repairing it or replacing it with something else?

[TerrA LX]

What gives with the watt's? (sorry about the pun)

[EunUCh]

The watts will be determined by the voltage across the resistor coil multiplied by the current flowing through the coil.P(watts)=V(voltage) x I(current).

The current through the coil will be the same as what the motor is drawing(current is the same in a series circuit).

There was another thread on this somewhere,i think they made one,you can get special resistance wire to repair them or make another one.

[TerrA LX]

Whatt with my limited knoledge of lectrity i never heard of any input Watts rated, only ever output.

[r2160]

I am repairing mine as after pulling the heater apart, we found the coil was broken.

 

The special wire you are thinking of is Nichrome wire. However, the biggest issue is knowing the resistance required. The resistance is important as it sets the slow speed part of the fan.

 

Watts and power really dont matter in this case.

 

cheers

Glenn

[Rockoz]

Watts still matter. Or in particular the current draw.

Like many things Nichrome wire comes in many sizes.

Too small csa and you will find it doesnt last very long.

[EunUCh]

you will need to know the ohms/foot of the wire,stretch it out and measure the ohms on 1 foot of the wire
then work out the total ohms of the coil then use same wire.
We used that wire for dummy loads when testing amplifiers..it used to glow with a good amp.

[EunUCh]

Jacar sell only one size by the look of it (ww4040), another way to measure the resistance of the coil is to measure the wire diameter and the length of

the coil and use the chart on Hmwire site to calculate the resistance, the resistance of the diameter of the wire is given in ohms/inch and looks like

there are different grades.

Once you know the length and diameter multiply the length in inches by the ohms/inch of the wire gauge used and that should give you a pretty good idea, if you get a bit

technical you will even be able tell what grade they used.

You could work it in ohms/mm to give an even more accurate reading.

 

this needs to be in electrical

[Rockoz]

Lets assume that the heater fan draws 6 amps.

If the required resistance is 2 or 3 ohms we can calculate the power.

P =IxI xR

6x6x2=72watts

So to allow for a little redundancy lets say 80watts.

Best off the shelf resistor I have seen Jaycar stock is 10 watts.

So to handle the power we need 8 in parallel.

To get the required resistance will then need 8x16 ohm or 24 ohm resistors

Available values off the shelf around the size will be 18 or 22 ohms.

These resistors are roughly 10mm square and around 50mm long.

Quite a package to have to hide.

[r2160]

problem is that we don't know how much current the fan draws at the slower speed.

 

glenn

[shadey1963]

Might get something from here

 

http://www.gmh-toran...eater-resistor/

 

Steve

[hanra]

Here is my big Torana fan on the bench at full speed.

[S pack]

Nichrome wire

http://stores.ebay.c...fsub=1837868016

[EunUCh]

Just goin on Hanras post and using a round number of 4 amps on hi speed,if we assume that the
motors are the same the resistance of the motor at 13.2V @ 4A is 3.3 ohms.

If we also assume that half speed or thereabouts we need 2A,but because of inductive loading and
friction from bushes and a fan pushing air we would need more current,closer to 2.6 amps to overcome the load.

If this is correct then 2.6A through a 2 ohm dropping resistor will give give a 5.2V drop across the resistor coil
which equates to roughly 13.5Watts that the resistor coil needs to dissipate (not allowing for the resistance to go up as the wire heats).
looking at the picture from the other thread it looks like you could stretch that wire out to over 3 foot.

I still think the easiest way is to stretch the wire and measure it up...it is broken now and needs repair either way.

[EunUCh]

I don't know if this will help at all...if you can measure the current drawn on the high speed circuit and it turns out to

be 4 amps or just under the motors would be pretty close in specs.

I get 4A on a battery on charge at 14V on the high speed,i get 2.8A on low...this is on a UC fan motor but current is current as is voltage.

 

When you didle the the numbers i get a resistance of 1.5 ohms that is needed,when the wire heats up this resistance will go up.

I would say that 2-3 ohms would be safe.