Parts needed with switch to 12 volt system

[koates]

Hi there, I think there are a couple of people on here who are not looking at the correct picture. If you have a 6 volt wiper motor that draws 3amps on 6volt supply and then you apply 12volts to the 6volt wiper it will draw 6amps current. So you need to reduce the voltage and current flow to the 6volt wiper motor by placing a resistor or voltage control in series to reduce the 12 volt supply back down to 6volts. You could of course fit a 12volt wiper. THIS SITUATION IS ONLY AN EXAMPLE. I am not going to post on this again because I am correct. Please do your homework before posting incorrect information chaps. Regards, Kevin.

[HCO41]

Sorry koates, I can't go along with your interpretation of ohms law. Mike agrees that if the voltage doubles the amps are halved but in his second post the 6V example should result in .5 amp. Jack agrees with koates but in his example using the same formula, I think we all agree on, (I=E/R), he comes up with half the amperage with 12v than his result with 6v.
If using a motor as an example, I just went to the shop and read the data plate on one of my compressor motors. The data plate shows 37amps if hooked up to 120volts, 18.5 amps if hooked to 220volts.
Have it as you will but if the resistance stays the same there's no math I know of that will change the result (voltage doubled,amperage halved) using I=E/R.
No insults intended.

[Jack E/NJ]

HCO41>>>The data plate shows 37amps if hooked up to 120volts, 18.5 amps if hooked to 220volts.>>>

Yes, in a dual voltage motor there are two taps on its windings that give two different impedances(resistances). One tap is used if wired for 110v. The other tap is used if wired for 220v. The impedance of the 220v tap is approximately twice the impedance of the 110v tap so that the power output of the motor is about the same whether connected to handle 110v or to handle 220v. Power is defined as P=IE so, yes, the motor will draw half the amps at 220v as at 110v if the taps are connected properly. However, if you try to apply 220 volts to the lower impedance 110v tap, you will likely burn out the motor, since you will exceed the amp capacity of the 110v windings by a factor of 2.

In my previous post the 6v example results in 0.5 amp, and the 12v example results in 1 amp in accordance with I=E/R. That is, the 12 volt current is twice the 6v current for the **same** impedance.

Hope this helps.

Jack E/NJ

[HCO41]

Thanks Jack, I got so hung up on the original discussion that I forgot about the different impedence in the 220/110 motor windings. I remember the diagrams for the two options on the underside of the junction box and of course wired both compressors 220.

[mralternator]

An alternator ONLY produces what is asked for by the system and the loads, if a 100 amp alternator is on your car and you only have a 20 amp load , it will ONLY supply the 20 amps needed/asked for/allowed by the Regulator, and while running the alternator supplies directly to the loads, and only back to the battery to fully charge the battery. your amp meter will read at start up around +10 or less depending on battery state of charge, to replace the initial starting power taken from battery, Then meter will lower to around 3-4 and eventually 0 , meaning your battery is fully charged and all the loads are being handled by the alternator

[mralternator]

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[mralternator]

and why have vehicles been adding 42 volt charging systems? Because they can use less wire. and supply more loads efficiently,,,why? volts is pressure , amps is flow, a higher pressure supplies more quantity at a faster speed, . the rule is High voltage low amperage, and vice versa, example , when you lug , slow crank a starter it draws MORE amperage and heats up , burns contacts, be cause of the lower voltage. and Higher amperage draw, think of the electricity as water flow and you'll make it much more simple to understand

[mralternator]

The total electrical load becomes half of what it was originally because of the electrical rule that says when you double the voltage the amperage load will be reduced by half

[Jack E/NJ]

Correct! So as to try to better clarify this discussion, the load mralternator referred to are the amps. This rule applies when the power level at the higher voltage is desired to be approximately the **same** as the power at the lower voltage. Since P=IE, the amps at the higher voltage will be less than the amps at the lower voltage for the **same** power level. As mralternator infers, less amps producing the **same** power level at the higher voltage means there are usually less high current wire & connector heating losses throughout the electrical distribution network.

Jack E/NJ

[Mike51Merc]

You guys are right and I'm getting rusty. I was thinking about Watts (the work performed) without appreciating the fact that the appliance is going to "work" twice as hard with double the voltage.

If the "work" is constant, then doubling the voltage will halve the current. In this case the work is going to double--- like a 6 volt bulb burning twice as bright---therefore also doubling the current.

[BUBBAS IGNITION]

Originally Posted by Jack E/NJ

Sorry, koates is still correct. E=IR. Thus I=E/R. So in your 12 ohm resistance example
I (@ 6v) = 6v/12 ohms = 0.5 amp
and
I (@ 12v) = 12v/12ohms = 1 amp

Jack E/NJ

Correct !!!

[bobH]

Koates and Bubba, and some others, are still correct. And, the wiper motor analogy is correct. But some folks are missing the boat on the gauges. Please re-think how they work (referring to original Ford gauges here). And, ohm's law has less to do with the gauge situation.

[Jack E/NJ]

bobH>>>And, ohm's law has less to do with the gauge situation.>>>

And you are also correct because many of the old gauges & sensors work by responding to heat, either thru a bimetal strip and/or change in resistance. So heat can complicate things when using a reducer in a 6v guage circuit so it can accommodate 12v. In other words, the gauge circuits at 12v with reducers may respond differently than they do at 6v. But hopefully the reducers will protect the 6v circuits from being fried when they're asked to operate at 12v. 8^)

Jack E/NJ