warn 6hp motors running 24v

[dirtydiesel]

Tried unsucsessfully to put 24v through a std wan 6 hp motor this weekend, it lasted less than 20 mins. impressively quick but didn't last. motor is just over a year old and had been inspected and rebushed prior to fitting.

Anyone got a solution?

[will_warne]

Silver soldering all the joints apparently solves it. How hot was it when it failed? I think a few guys down under as well as in the far east run this sort of setup. I'm going to start doing some research on places like outerlimits and pirate. I'll be very interested to see how you get on.

[andylandy]

i used 12 volt motors and a 24 volt batt set up on the rfc all i used was goodwinch albrights and 5.6 bow moters pulled like mad

it worked for me

[will_warne]

What were your longest pulls? How hard? 12 or 24 V Albrights? What about lowering out, that'd be scarey at nearly twice the speed?

Sorry about all the questions but I'm thinking about doing something along these lines.....

[Michele]

i used 12 volt motors and a 24 volt batt set up

How can it be?

Sheer curiosity,I always had the idea (my ignorance) it wasn't possible.

I mean,dropping a 24V battery straight in the slot,wire the winch and you go...

[will_warne]

Ah yes, but with around twice the speed and torque. However, current draw is the same as a 12V motor so power is doubled and so heat builds up twice as fast meaning half the duty cycle.

[BogMonster]

Current draw should be doubled too surely, so giving 4x the power?

basic Ohms theory if you double the voltage through a fixed resistance then you will also double the current, and since power = voltage x current - 2 x 2 = 4.

or maybe series wound motors behave differently...?

Bet the buggers go though, whichever it is

[will_warne]

Boggy, current stays the same with 12V flowing through, or so I understand it.

[andylandy]

in standard set up its a 24 volt winch system ie altanater allbright winch motor

and all i done was put a 12 volt motor on the front winch

f***ing hell its fast

and pull

well a stanard 12 volt set up will pull the thong of a loose woman like jordan

my set up would get the big pants off a nun

[LR90]

Guess as long as you have a bif enough supply and can swap them out quick enough it sounds like a darn fun idea

BTW Will I think Steve is right on this one even from his armchair. Twice the current and four times the heat and power. Not surprised the smoke escaped.

[simonr]

I seem to remember explaining this a few days ago on another thread on here!

Have a look at: Paul Hills Motor Explanation

It gives you a lot of useful info to calculate what your motor will do if you double the voltage.

In short, if you double the voltage, for a given torque, you will double the speed.

The torque is proportional to the square of the current, so if you double the voltage, you double the current (by ohms law), but you quadruple the stall torque.

For a given load, the current will be the same in both 12v and 24v (since torque is not related to voltage).

Since the line speed has doubled for this torque, you should only have to run the motor for half as long. It thus, for a given recovery will generate half the heat (same wattage for half the time) - this is where the potential efficiency gain comes from.

The problem comes from the fact that you have 2 x speed & 4 x torque available and you will probably use it! If you do, without reducing the duty cycle, you will cook the motor.

Silver soldering the joints inside the motor only increases it's life a little as the enamel on the wire will melt around the same temperature normal solder melts. A lot of decent motors use welded contacts anyway.

If you over-volt a motor and treat it properly, it will last every bit as long as one not over-volted - and you will still get the higher performance. If you move outside it's performance envelope, you will however cook it far quicker than the non overvolted motor.

Si

[BogMonster]

There speaketh a Robot Wars man who blows up motors for a living

[simonr]

blows up motors for a living

Thought it best not to mention that!

Simon & I were talking about this in the pub - how to make a controller which would safely run a 12v motor on 24v

The best answer so far is effectively a switch which switches the motor on and off very fast with a 50% duty cycle.

This would give you the same top speed as running on 12v, but twice the torque - so the same gain as running a pair of 12v motors.

Additionally, it would be easy to make it act as a speed controller so you could vary the speed from zero to 50% - might be useful?

The down side of this is likely to be cost. I reckon you'd need a PIC controller, high side driver, opto-isolator and a bank of 20 mosfets on a heatsink to give you 500A continuous rating. That would probably cost best part of £100 to build.

Then we went on to talk about adding a second motor - no, not copying Jim - a two stroke petrol engine. Only connect the spark plug when the electric motor is running. The electric motor will start it (in either direction) and it will provide additional torque while the eleccy motor is running. It would probably need to be geared down a bit to be useful though.

Four stroke would develop more torque - and best of all would be a little two stroke diesel!

Food for thought!

Si

[Hybrid_From_Hell]

Si

Stop mucking about with a silly 2 stroke, shove a nice V8 on it

Then again, suppose winching in the water it would misfire

Oh well.................

Nige

[BogMonster]

The 115hp 2 stroke that my outboard motor has in it would probably get a decent line speed

only problem would be that you'd have to winch underwater for cooling

[Hybrid_From_Hell]

The 115hp 2 stroke that my outboard motor has in it would probably get a decent line speed

only problem would be that you'd have to winch underwater for cooling

sorted

fit one of each, twin motor winch set up with SCLs outboard on one and a Eales V8 on the other

Nige

[darthdicky]

Might be a silly idea, but how about running the winch on 12v until it comes under heavy load, then flick a switch to give 24v? Could also go to 24v if you need more speed, but you're not running it like that all the time so shouldn't have a problem overheating it?

Richard

[Tomcat Nev]

Simon & I were talking about this in the pub - how to make a controller which would safely run a 12v motor on 24v

The best answer so far is effectively a switch which switches the motor on and off very fast with a 50% duty cycle.

This would give you the same top speed as running on 12v, but twice the torque - so the same gain as running a pair of 12v motors.

Additionally, it would be easy to make it act as a speed controller so you could vary the speed from zero to 50% - might be useful?

If you use a form of 'Chopper' control for a DC motor you will loose the speed because with the motor will react to the Average or RMS (can't remember which for some strange reason) of the applied voltage.

Therefore at a 'Chopped' 50% 'duty cycle' you will have approx 50% of the applied voltage.

This is how trains accelerate. Modern that is old DC uses resister banks!

So you could use a chopped supply in the form of a Thyristor or modern equivilent which is turned on and off by a variable frequency supply in a controller. This would achieve speed control with a winch but if it were flat out then the same over heating issues still apply!

In the end the only way of solving the over heating is to use a motor with a greater current capacity!

I suppose then people would run the things at 36V and be back in the same situation.

Nev

[dollythelw]

oddball logic time, a chopped supply may work on rolling stock but that has momentum in between chops, a stuck vehicle has none, using a chopper will (I would have thought) just produced a pull that directly reflects the input power - chop at 50% = 50% pulling power

[BogMonster]

sorted

fit one of each, twin motor winch set up with SCLs outboard on one and a Eales V8 on the other

Nige

I see the logic there, when the V8 died once it was within 100 yards of a puddle you could kick in the outboard and keep on pluggin'

Amazing how resilient petrol outboards are to water (be a bit of a bugger if they weren't I suppose...), it makes you wonder why V8s cause so much trouble. Its early days yet so I haven't "stuffed" mine but there are plenty of stories on RIBnet of people stuffing their whole boat under huge waves and coming out the other side with engine(s) still going fine, after everything (including the air intakes) have been completely under water for several seconds! There was a discussion on there recently about fitting a snorkel to an outboard too...

[Bush65]

The 6HP motor is known for creating a lot of carbon dust (from the brushes). To prevent the dust from building up and causing a short circuit, blow low pressure air through the motor from the gearbox end and out of the end cover. This also helps with cooling.

[will_warne]

Just to get really off topic, how about a smallish (about 1000 - 1500cc) diesel engine running through a CVT transmission, connected to a switchable front/rear transfer box then connected to drums at each end of the vehicle....... Relable, uber fast and independent of the driven engine. Now just build a vehicle to deliver said winch to the stuck situation and heah presto.

Bush, what alternatives to the XP motor do you have down under?

[simonr]

oddball logic time, a chopped supply may work on rolling stock but that has momentum in between chops, a stuck vehicle has none, using a chopper will (I would have thought) just produced a pull that directly reflects the input power - chop at 50% = 50% pulling power

Almost right.

The chopping is much faster than the motor can speed up and slow down - generally between 10 and 20 thousand times a second. It is not relying on the momentum of the motor so much as the magnetic hysteresis in the electromagnets that make up the motor.

If you were running on 24v, you would get twice the speed, but 4 x the torque.

If you chop the motor supply with a 50% duty cycle, you get half the speed and torque.

However, that still gives you the same speed as on 12v, but with double the torque (1/2 x 4 = 2).

The power is a square relationship. If you double the voltage - you quadruple the power. If the motor is only running half the time, you get half of that i.e. 2 x the power.

Nev,

There are problems with Thyristors. You still need a chopper (or an AC supply) in order to make them switch off (when you switch one on, it will stay on until the current flowing drops to zero). There are ways around this like using 'gate switch-off thyristors' (expensive and low current) or a thing which generates a negative going transient spike on the supply lines sifficient to instantaneously stop the current flow (good for zapping other bits of equipment).

A DC motor with a commutator you might think interrupts the current as the commutator switches from one set of poles to the next. This is true some of the time, but with big multi-pole motors, there are always several sets of coils in use and the current never drops to zero.

This is the way to do it without Mosfets! Something I tinkered with in the past!

Mechanical Speed Controller

Si

[dollythelw]

ahh so you keep the coil soaked so dont run into excessive henrys?

or have I got the wrong end of the stick (as usual)

I go back to me bailer - she work on diesel

[simonr]

ahh so you keep the coil soaked so dont run into excessive henrys?

Very clever!

Si