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[SolentSurfer]

I would have thought this would be a common problem but I can't find many references to it.

I'm looking for an easy way to step down a 12v supply for a 7.2v bow thruster. I know Action Electronics have a solution in the P93 Multi Controller, but this seems quite expensive and from what I can tell does not provide speed control over the thruster, just full on in each direction at full throw.

Any help appreciated.

[FullLeatherJacket]

I know Action Electronics have a solution in the P93 Multi Controller, but this seems quite expensive and from what I can tell does not provide speed control over the thruster, just full on in each direction at full throw.

It does if you use Mode 2 (50% ESC ouptut). The alternative is a 12v/7.2v DC/DC converter or an equivalent voltage regulator which will carry 5A+. If you find any at a reasonable price can you please let us know?
Easier to fit a separate 7.2v battery pack, I'd have thought - you can then raid your junque box for an ESC.
FLJ

[Lt. Raen]

Wouldn't the most simple way be to use a resistor to bring the voltage down to the motor?

I know this would require some testing to ensure a resistor of the correct value is used, and so that it doesn't limit the current too much but if he wants a really simple way to step down would this work

I believe a resistor of 66 to 70 ohm should be enough, but im sure someone out there will enlighten us :)

After all resistors only cost pennies

Just a thought,
Tim

[DickyD]

You can always tell an Aussie.

Not much though.

[Subculture]

Can't you get a 12 volt motor that will fit?

[Lt. Raen]

Dicky I don't get your reply, whats "not much"??? (I'm sure it will be blatantly obvious when you point it out to me  )

Tim, thoroughly confused

[Tugwilson]

the clue was in the you can alway tell an Oz.....you can tell them but not much cos they seem to know it already was what he ment. and it was only a leg pull not ment. I know Dick.

[Lt. Raen]

Haha ah right fait enough makes sense now 

Tim

[FullLeatherJacket]

I believe a resistor of 66 to 70 ohm should be enough, but im sure someone out there will enlighten us :)

Your calculation is a bit out, sport. Ohms Law gives a resistance of approx 1 Ohm @ 5Amps. The problem is that the power is I²R which, in this case, is 25Watts. This is all dissipated (=wasted) energy in the form of heat, and it's ON all of the time so would soon flatten your power supply for no real advantage.
That's why we use electronic speed controllers and not rheostats to control the speed of our 'leccie motors.
Suit yourself.
FLJ

[Lt. Raen]

Ah see I knew here was a reason that my simple solution wouldn't work. But it would have been great if it did 

thanks for clearing that up FLJ
I got the resistor value off a program quickly so didn't check it through (dad will shake his head at me for at  )

cheers, Tim

[SolentSurfer]

Thanks all for your comments. A separate battery pack and speed controller is probably the best way forward - could do with the ballast anyway!

[portside II]

Dave will probably put me right on this ,but the standard 7.2v motor that comes with bow thrusters , is it not capable of handling voltages above and below what it states .
Like the MFA type that are 5-15v (for example) and the mid voltage is 10v , but you wouldn't ask for a 10v battery to power it .
I have used these thrusters on 12v and they work fine with an ESC , just lower the throw's to suit the boat its fitted to .
daz

[SolentSurfer]

Dave will probably put me right on this ,but the standard 7.2v motor that comes with bow thrusters , is it not capable of handling voltages above and below what it states .
Like the MFA type that are 5-15v (for example) and the mid voltage is 10v , but you wouldn't ask for a 10v battery to power it .
I have used these thrusters on 12v and they work fine with an ESC , just lower the throw's to suit the boat its fitted to .
daz

Now that sounds like it's definitely worth a try, great idea, thanks.

[FullLeatherJacket]

I have here a box which held a Graupner Speed 400 7.2v i.e. the same motor as is fitted to their Bow Thruster. Its nominal voltage is 7.2v while its Operating Voltage Range (Direct Drive) is given as 3.6v-8.4v. A fully charged 12v SLA is a shade under 14v.
By all means run one on 12v but you have then to resist the temptation to shove the stick all the way over and leave it there. Also bear in mind that removing one of these motors from the rest of the thruster in situ is a pain - if not downright impossible.
Like the man says, suit yourself (and I wouldn't dream of putting Daz right - he's bigger than me!).
FLJ

[SolentSurfer]

Thanks, makes sense. I guess I either measure the outputs from the ESC and set end points accordingly as Portside II suggests - or maybe even look at swapping the motor before initial fitting.

[Tug-Kenny RIP]

I queried your problem when I was building my Severn.

Bow thrusters seem to have a desire for 7.2 volts.  An awkward problem then and still is, .... as you're finding out. You would think the designers might have realised this at the time.
 
Most of the folks need a bow thruster for larger, slower type of craft, and are not interested in using 7.2 volts.

My solution was to fit a separate 6 volt battery just for it's needs, which involved extra wiring and controlling circuitry.  All a pain, because of this.

As you can use some ballast then this is the way to go.  Running your motor on 12 volts, no matter how tender you might think you'll be, will lead to trouble eventually.

Hope this helps

Ken





 

[SolentSurfer]

I queried your problem when I was building my Severn.

Bow thrusters seem to have a desire for 7.2 volts.  An awkward problem then and still is, .... as you're finding out. You would think the designers might have realised this at the time.
 
Most of the folks need a bow thruster for larger, slower type of craft, and are not interested in using 7.2 volts.

My solution was to fit a separate 6 volt battery just for it's needs, which involved extra wiring and controlling circuitry.  All a pain, because of this.

As you can use some ballast then this is the way to go.  Running your motor on 12 volts, no matter how tender you might think you'll be, will lead to trouble eventually.

Hope this helps

Ken

 

Thanks, I guess your right. If it will run OK at 6volts, it would probably make sense to use the Action Electronics P93 Multi Controller - can work as ESC at 50% main power. Although quite pricey, probably no more than separate ESC and battery (and charger), probably be a bit tidier and saves charging another battery.

[fatcat123]

I again faced the same issue but used the P93 on mode 2. Works a treat. Money is money, lets not forget this is a hobby and theres no point not being unhappy with the installations on the build. Worth every penny i reckon.

Dan

[portside II]

I have here a box which held a Graupner Speed 400 7.2v i.e. the same motor as is fitted to their Bow Thruster. Its nominal voltage is 7.2v while its Operating Voltage Range (Direct Drive) is given as 3.6v-8.4v. A fully charged 12v SLA is a shade under 14v.
By all means run one on 12v but you have then to resist the temptation to shove the stick all the way over and leave it there. Also bear in mind that removing one of these motors from the rest of the thruster in situ is a pain - if not downright impossible.
Like the man says, suit yourself (and I wouldn't dream of putting Daz right - he's bigger than me!).
FLJ

Not from the side view buddy 
daz

[FullLeatherJacket]

Not from the side view buddy 
daz

Now did I say that? OK - so you're the taller standing up, but I'm taller than you lying down..........and I'd beat you in a Roll the Big Bloke Down the Hill competition. 
FLJ