Switching from 12V to 24V

[transmitterdan]

Clive,

Unless the 12V fan is designed for dual voltage it will burn up rapidly on 24V. The fans designed for dual voltage have internal regulation. They don't "spin faster on 24V".

[coopec43]

Originally Posted by transmitterdan

Clive,

Unless the 12V fan is designed for dual voltage it will burn up rapidly on 24V. The fans designed for dual voltage have internal regulation. They don't "spin faster on 24V".

For $A24 ($US18) do you really think they would be that sophisticated?


Clive

[CatNewBee]

Originally Posted by coopec43

For $A24 ($US18) do you really think they would be that sophisticated?


Clive

I don't know, but maybe they have a simple power selector switch and a resistor or some more copper coil wingdings for the 24V setting - it is not rocket science. A simple PTC thermistor in series to the motor can also be used to limit the current and protect the motor when connected to 24V. Or even simpler - they are 24V motors running slower on 12V.

[coopec43]

"Or even simpler - they are 24V motors running slower on 12V"

Probably pretty close to the truth. (But halving the voltage will double the amps so I hope the motor can take the increased amperage)



Motor voltage

If you run a 12v motor from 24v its current drain and speed will still depend on the mechanical loading. However under no load it will now run at twice the speed at which it originally ran with 12v. Heating in the motor is still related to the current – so you can still run it at its full rated mechanical load/current. However if the motor is badly balanced you may expect noise and vibration as the general construction may be inadequate for the faster speed. There may also be a problem with brush wear since the brushes are being asked to switch the current twice as fast. These effects are, however not very likely and usually the speed increase is quite OK.

https://www.4qd.co.uk/docs/12-24-36-or-48v-operation/


Clive

[coopec43]

Well I thought I'd be pushing things a bit far running 12v pumps on 24V but this guy is doing it!

"We are a 24v Boat.

Look in the back of Marine stores for bargains as sometimes a 24v item might sit for years on the shelf, and be cheaper than a faster moving 12v item. Eg. We bought 2 electric heads for $150.00 each.

The wiring is already oversized = good.

Bilge pumps, shower pumps etc, just put the 12v version in, they love the low amperage and pump like crazy."

http://www.cruisersforum.com/forums/...4v-conversion-
176755.html

Clive

[coopec43]

SOMETHING WENT WRONG WITH MY PREVIOUS POST AS THE LINK WOULD NOT WORK NO MATTER WHAT i DID. NOW IT WORKS?


Well I thought I'd be pushing things a bit far running 12v pumps on 24V but this guy is doing it!

"We are a 24v Boat.
Look in the back of Marine stores for bargains as sometimes a 24v item might sit for years on the shelf, and be cheaper than a faster moving 12v item. Eg. We bought 2 electric heads for $150.00 each.

The wiring is already oversized = good.

Bilge pumps, shower pumps etc, just put the 12v version in, they love the low amperage and pump like crazy."

THIS LINK NOW WORKS
http://www.cruisersforum.com/forums/...on-176755.html


Clive

[CatNewBee]

Originally Posted by coopec43

...

The pumps etc, just put the 12v version in, they love the low amperage and pump like crazy."
...

Clive

Crazy, indeed.

What makes you think, a 12V pump would run on 24V on lower Amperage? The current will not drop - the oposite is the case Voltage drives the current, the power will increase even more (voltage * current), that is the reason it runs faster. Btw, it is the current alone that creates the magnetic field what creates the motion of the rotor, not the voltage - if it runs faster this means a higher current is flowing through the coil.

I would suggest you do some reading about electricity and electro-magnetic fields.

[coopec43]

Originally Posted by CatNewBee

Crazy, indeed.

What makes you think, a 12V pump would run on 24V on lower Amperage? The current will not drop - the oposite is the case Voltage drives the current, the power will increase even more (voltage * current), that is the reason it runs faster. Btw, it is the current alone that creates the magnetic field what creates the motion of the rotor, not the voltage - if it runs faster this means a higher current is flowing through the coil.

I would suggest you do some reading about electricity and electro-magnetic fields.

QUOTE What makes you think, a 12V pump would run on 24V on lower Amperage?

OK tell me where I am going wrong. If a 300W pump runs on 12V the Amps will be............25A. Correct? If the same pump (300W) runs on 24V the Amps will be.........12.5A? Am I wrong?

I agree with what this Electrical Engineer says although I suppose there are technical reasons why a motor running on 24V would use more power overall.

"Yes, the pump will run faster on 24 V than on 12 V. It will draw more power, but also pump the water faster. However, the overall energy spent to pump the same amount of water will still be higher at 24 V than at 12 V, even though the 24 V is on for a shorter time".

This is where I get confused: are you able to explain in simple terms?

Motors don't behave the same as resistive loads like lamps or heater elements, they are inductive, and as the motor turns it produces back EMF, which reduces the amount of power required to maintain that speed.

Clive

[CatNewBee]

Originally Posted by coopec43

QUOTE What makes you think, a 12V pump would run on 24V on lower Amperage?

OK tell me where I am going wrong. If a 300W pump runs on 12V the Amps will be............25A. Correct? If the same pump (300W) runs on 24V the Amps will be.........12.5A? Am I wrong?

I agree with what this Electrical Engineer says although I suppose there are technical reasons why a motor running on 24V would use more power overall.

"Yes, the pump will run faster on 24 V than on 12 V. It will draw more power, but also pump the water faster. However, the overall energy spent to pump the same amount of water will still be higher at 24 V than at 12 V, even though the 24 V is on for a shorter time".

This is where I get confused: are you able to explain in simple terms?

Motors don't behave the same as resistive loads like lamps or heater elements, they are inductive, and as the motor turns it produces back EMF, which reduces the amount of power required to maintain that speed.

Clive

Wrong. Take an Ammeter and check it out. Or just reduce the voltage to zero. According to your assumption, current will climb to infinite and earth will implode in a singularity.

No, really check some good old physic textbook. increasing voltage causes increase of current, simple law. Even coils are not ideal linear resistors, they are resistors. Because both voltage and current rise almost linary, the power as product of both rises exponentially and potentially destroys the unit.

The resistance of a coil increses only with increase of frequency and this opposes the linear rise of the current a litle, but not to the extent, that the current cuts to half. When applying a Voltage to a coil the current is delayd due to self-induction, because the creating of the magnetic field causes an induction of a current to the coil in opposite direction what "brakes" on the power of the field, so it delays the build up. That is the reason why coils are non linear resistors. Running at higher rpm means performing more work at the same time, so wattage will be higher current will rise not that quick than voltage because of the higher frequency, but it will rise.

[transmitterdan]

Clive,

DC motors don’t behave as you believe. If you increase the voltage the current and speed will also increase. There are motors that have an internal electronic speed controller and they may be designed for dual voltage. But a plain DC motor draws more current the more voltage you give it. And it gets 4 times as hot for twice the voltage.

AC synchronous motors may operate as you describe but only over a narrow range of voltage. You cannot double the voltage of an AC motor and expect the current to drop by 1/2. To achieve that the motor windings have to be rearranged. Many AC motors have a junction box where that rewiring is done.

But no plain motor with just wires and magnets inside can operate for long at twice it’s rated voltage. Anyone telling you different is confused.

[coopec43]

[QUOTE=transmitterdan;2766640]Clive,


DC motors don’t behave as you believe. If you increase the voltage the current and speed will also increase.


But that is what I said.


AC synchronous motors may operate as you describe but only over a narrow range of voltage. You cannot double the voltage of an AC motor and expect the current to drop by 1/2. To achieve that the motor windings have to be rearranged. Many AC motors have a junction box where that rewiring is done.

Sorry! We are talking about boat electrical motors so I should have made it clear I was referring to DC (Direct Current) motors. My apologies......

Clive

[transmitterdan]

Clive,

For avoidance of doubt, if you run 12V bilge pumps on 24V there is a serious serious risk of fire. Motors inside bilge pumps are designed for a given maximum voltage. Exceeding that voltage will destroy the motor in a relatively short time.

[coopec43]

[QUOTE=transmitterdan;2767023]Clive,

For avoidance of doubt, if you run 12V bilge pumps on 24V there is a serious serious risk of fire. Motors inside bilge pumps are designed for a given maximum voltage. Exceeding that voltage will destroy the motor in a relatively short time".


Thanks for that. I wouldn't mess around with voltages on bilge pumps where maybe a life depended on it.

Although others do it I'd be reluctant to use 24V on a 12V diaphragm (say) galley pump. (I wouldn't worry about the motor but I'd be worried the diaphragm wouldn't be able to handle the higher RPM).

As a matter of interest I checked the weight of a Rule 3700 GPH bilge pump - the 12V, 24V and 32V models. I would have expected the 12V model to be heavier than the other two (having heavier winding) but they are all the same weight at 5.4lb. Maybe a production line expediency.............?


Clive

[CatNewBee]

not surprising. Higher voltage motors have thinner copper wire with more wingings for the same power to cope with the higher voltage and less current, the weight remains the same in the end.

Because the current needs to be lower (thinner longer wire means higher resistance), you need more windings to produce the same strength of the magnetic field for the same power.

[coopec43]

CatNewBee


Thanks for that! (It was going to keep me awake all night)


Clive