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Old 04-01-2020, 11:06 PM   #32
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Join Date: Sep 2016
Location: Melbourne Australia
Posts: 321
Default Re: Electrical schematic request - 41 Convt. electric top

OK, lets see how good my memory is (it's been a while since I have done any electrical figgerin').

As I said earlier, I'm looking to do a12V conversion and don't want to damage the 6V top motors. They should be OK on 12V given the short duty cycle, but I'm risk averse and it could get expensive If I damage them.

Using a DC current clamp meter, I get a reading of 27A for both motors when the top is commencing to rise. I'll call this Full Load current. When lowering the top, I get a reading of 19A for both motors - I'll call this low load.

Ohm's Law specifies: Resistance=Volts/Amps so if I want a 6V drop:

Full load R= 6/27 = 0.22 Ohm resistor.

Low load R= 6/22 = 0.27 Ohm resistor

I'll assume a 0.25 Ohm resistor which should give me anywhere between 5.25V at the motors on full load and 6.5V at the motors at low load.

So, a 0.25 Ohm resistor should do it?

What power rating? Ohms Law specifies Power = Current squared X Resistor, so:

Full load Power = 27X27X0.25 = 182W. The resistor is going to get 'real warm'.

If I parallel two 0.5 Ohm resistors I get 0.25 Ohm. Each will share the power so will dissipate 91W of heat each.

If I parallel two 0.5 Ohm 200W resistors I should be OK?

What say you? I'm a little rusty, so if anyone can run a flinty eye over these numbers I'd appreciate it.

Last edited by fortyonerag; 04-02-2020 at 01:08 AM.
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