I'm running a 12v bilge pump on a 24v system

[Rusty Jones]

Originally Posted by Fuss

There is no electronics in in, just a motor.

It seems to work fine and spins faster too.

So I just thought I would ask you experts what I am missing??

I like to entertain myself reading the Geniuses that can prove they know everything! Fact is the Bilge pump motor will draw the same wattage no matter the input voltage! That Fact is Standard of the PIE wattage equation! The genius with all the math equations is forgetting about is the resistance in the system remains constant! it does not change with voltage change that is why the motor runs faster with 24 volts. Fact is the Amperage will be half!!!!! The heat will be increased by friction in the bronze bushings! The fact is the armature has a preset number of loaded revolutions built into the bearing material! An expensive pump should have higher quality parts hopefully better alloy bearing but not always so what you need to go home with as the motor runs faster ( twice as fast) the amount of run time will be half for a 12 volt bilge pump as to a 24 volt bilge pump. The windings in a 12 volt pump will be 2 gauge sizes larger than a 24 volt pump. not enough difference in size to feel the weight difference. the armature will see no harm but the pump will fail to run when the bearings are worn out! Just like when you operate on the proper voltage. you should ALWAYS have a new bilge pump on board. Fact it will work to put a 12 volt pump in a 24 Volt system but I would never put a 24 volt pump in a 12 volt system! that would not work well at all!!!

[Rusty Jones]

Originally Posted by seabear2

24v will double the current and cause 4x the heat load. Assume your windings have 2ohms of resistance then the current load would be 12/2 = 6 amps. Heat load is The amount of amps squared times resistance. Therefore the motors windings must be able to handle 6x6x2 = 72 watts. Double the voltage then doubles the current to 12 amps with a resulting value of 12x12x2 = 248 watts of heat load. That much heat would probably result in damage to the windings of the motor. In the event it was submerged it might take the heat but I would operate it sporadically to allow time for it to cool so you would not lose the last available pump you had.

I like to entertain myself reading the Geniuses that can prove they know everything! Fact is the Bilge pump motor will draw the same wattage no matter the input voltage! That Fact is Standard of the PIE wattage equation! The genius with all the math equations is forgetting about is the resistance in the system remains constant! it does not change with voltage change that is why the motor runs faster with 24 volts. Fact is the Amperage will be half!!!!! The heat will be increased by friction in the bronze bushings! The fact is the armature has a preset number of loaded revolutions built into the bearing material! An expensive pump should have higher quality parts hopefully better alloy bearing but not always so what you need to go home with as the motor runs faster ( twice as fast) the amount of run time will be half for a 12 volt bilge pump as to a 24 volt bilge pump. The windings in a 12 volt pump will be 2 gauge sizes larger than a 24 volt pump. not enough difference in size to feel the weight difference. the armature will see no harm but the pump will fail to run when the bearings are worn out! Just like when you operate on the proper voltage. you should ALWAYS have a new bilge pump on board. Fact it will work to put a 12 volt pump in a 24 Volt system but I would never put a 24 volt pump in a 12 volt system! that would not work well at all!!!

[cal40john]

Originally Posted by Rusty Jones

I like to entertain myself reading the Geniuses that can prove they know everything! Fact is the Bilge pump motor will draw the same wattage no matter the input voltage! That Fact is Standard of the PIE wattage equation! The genius with all the math equations is forgetting about is the resistance in the system remains constant! it does not change with voltage change that is why the motor runs faster with 24 volts. Fact is the Amperage will be half!!!!! The heat will be increased by friction in the bronze bushings! The fact is the armature has a preset number of loaded revolutions built into the bearing material! An expensive pump should have higher quality parts hopefully better alloy bearing but not always so what you need to go home with as the motor runs faster ( twice as fast) the amount of run thttp://www.cruisersforum.com/forums/editpost.php?do=editpost&p=2846619ime will be half for a 12 volt bilge pump as to a 24 volt bilge pump. The windings in a 12 volt pump will be 2 gauge sizes larger than a 24 volt pump. not enough difference in size to feel the weight difference. the armature will see no harm but the pump will fail to run when the bearings are worn out! Just like when you operate on the proper voltage. you should ALWAYS have a new bilge pump on board. Fact it will work to put a 12 volt pump in a 24 Volt system but I would never put a 24 volt pump in a 12 volt system! that would not work well at all!!!

Wow! We've been down this road before.

You say P=E*I rules how this works. Hopefully you think E= I*R is a valid equation. Re-arranging ohms law, I = E/R Substitute I in the power eqn with E/R from ohms law.
So now P = E*E/R
You say R is a constant. So convince me that P is the same whether V is 12 or 24.

[coopec43]

Originally Posted by cal40john

Wow! We've been down this road before.

You say P=E*I rules how this works. Hopefully you think E= I*R is a valid equation. Re-arranging ohms law, I = E/R Substitute I in the power eqn with E/R from ohms law.
So now P = E*E/R
You say R is a constant. So convince me that P is the same whether V is 12 or 24.

Cal

I'm trying to follow the equations but when Volts = V or E, Amps = A or I and Power = W (Watts) or P I get confused.

Let's say to pump a bilge dry it takes a 12V motor drawing 10 Amps one hour. So the motor must be 120 Watts?

With a 24V motor it would still be 120 Watts but the motor would only draw 5 Amps

The Resistance for the 12V motor would be 12/10 = 1.2 Ohms (R=E/I) and the resistance for the 24V motor would be 24/5 = 4.8 Ohms.

Now where have I gone wrong? (This is all new to me)

[transmitterdan]

Folks, this thread is full of lunacy.

Motors don’t magically halve their current when voltage doubles. To get that effect the winding configuration must be changed.

Can you run a motor for a short while with twice rated voltage? Yes, for a while. How long a while depends on the motor internals.

But let me repeat, there is no valid formula that says doubling voltage halves motor current. That is just plain wrong.

Motors don’t obey Ohm’s law so you can’t use that for any analysis either. To do a proper analysis requires knowing motor internal components which we do not and can not know.

Here is the answer to the OP: Yes, a DC motor will run at twice rated voltage for some time. The amount of time is unknowable.

[hellosailor]

All well and good to talk about resistance, but since this is electromagnetics not electrics, one also has to look at electrical RELUCTANCE, i.e. the effects of the changing magnetic field which will of course change more vigorously as the voltage as increased in the windings and the rotor spins faster.

Ignoring all the nice theories, any electric motor shop or supplier will tell you that overvolting a motor will make it run faster. And, burn out faster. We knew that in middle school when we custom-wound slot car motors to make them run faster. No physics required.

But hey, if anyone doesn't believe it...So what, let them burn out the bilge pump. What's the worst that could happen? (Rhetorical question.)

[Jim Cate]

I'm an empiricist at heart! If you really want to get a handle on this, take the pump out of the boat, set up an experimental tub full of water, put the pump in it and run it for a few hours (if it lasts that long). Check it for wear, for overheating, for de-bonding of the impeller from its shaft and any of the other horrors that have been posited above.

It may do fine, it may die young, but you will have a better idea of its fate in use than if you listen to the theoreticians babbling away.

Jim

[coopec43]

Originally Posted by hellosailor

All well and good to talk about resistance, but since this is electromagnetics not electrics, one also has to look at electrical RELUCTANCE, i.e. the effects of the changing magnetic field which will of course change more vigorously as the voltage as increased in the windings and the rotor spins faster.

Ignoring all the nice theories, any electric motor shop or supplier will tell you that overvolting a motor will make it run faster. And, burn out faster. We knew that in middle school when we custom-wound slot car motors to make them run faster. No physics required.

But hey, if anyone doesn't believe it...So what, let them burn out the bilge pump. What's the worst that could happen? (Rhetorical question.)

Even with my limited knowledge of e̶l̶e̶c̶t̶r̶o̶n̶i̶c̶s̶
electromagnetics I would not have thought a DC motor was like a fixed resistor as there are such things as "counter EMF"etc.

But whether or not a 12V motor will burn out running on 24V surely depends on what it is used for? I'd quite happily run a 12V starter motor (or macerator?) on 24V. (I know first hand of a 12V starter motor in a Caterpillar Dynamo-meter shop that has been running on 24V for the last twenty years)

I'll be interested to see how long my 12V oscillating fans work for on 24V!!

[transmitterdan]

Originally Posted by coopec43

I'll be interested to see how long my 12V oscillating fans work for on 24V!!

I would be more interested in seeing what you tell the insurance company about the fire in your boat that started because of this experiment.

[Fuss]

I can't comment on the physics and formulas but I can talk from my experiences.

Firstly, the pump is running with water which is naturally cooling and also providing some turning resistance that limits the pumps revs. So i would imagine that a 12v pump running dry with 12v would maybe be worse for the bearings than a 12v pump pumping liquid with 24v. The revs would not be doubled because the liquid will limit its revs.

So these are different senarios to air fans and slot cars that pretty much would double their speed if the voltage is doubled and also have no cooling liquid.

What appears to happen when I put 24v through my 12v centrifical pump is the folllowing.....
it increases the revs
it increases the AH (but i did not measure this, however, I am sure it does.)
it increases the torque

So it pumps more water.

(I'm not recommending anyone does this though...I'm just reporting on my experience...so far)

I would like to pull 2 pumps apart and compare them, maybe I will do this when the pump dies....usually these pumps are losing performance after 2 years anyway even if you supply them with the correct voltage.

I'll report back on this thread once the pump dies.

[coopec43]

Fuss
You might be interested in this


https://www.metmotors.com/a-12v-dc-m...sus-24v-motor/

[transmitterdan]

Originally Posted by coopec43

Fuss
You might be interested in this


https://www.metmotors.com/a-12v-dc-m...sus-24v-motor/

You do realize that a 24V motor is different on the inside from a 12V motor? I ask because some posts seem to indicate you think they are the same item.

[Fuss]

Originally Posted by coopec43

Fuss
You might be interested in this


https://www.metmotors.com/a-12v-dc-m...sus-24v-motor/

Yes, I see that they say the differences between a 12v motor and a 24v motor means it halves the amps but we are not comparing this.

What we are comparing is a 12v motor getting 12v and a 12v motor getting 24v.

From my experience so far I think I see the following....
the 12v motor when it gets 24v does more work as it spins faster and has more torque and therefore I believe it uses more AH when it gets 24v.

[transmitterdan]

Yes it uses more power and does more work. Hardly surprising. But not recommended for mission critical apps and a serious fire risk too.

[Steve_C]

Originally Posted by transmitterdan

Yes it uses more power and does more work. Hardly surprising. But not recommended for mission critical apps and a serious fire risk too.

Will it work? in most cases yes

Should you? Not really unless its an emergency

You will never get one answer on this because it very much depends on the exact motor. Some will work for years with no problem, and others could burn up in minutes. Obviously not something I would recommend unless I had no choice and I could monitor it VERY closely, and then only until I could replace it.

As for the implications on current draw, it would be very easy to test, and again it could vary greatly depending on the exact motor used. Any actual results could not necessarily be applied to a different motor/pump/configuration.