[PSUBS-MAILIST] power converter

Tue Apr 26 22:53:08 EDT 2016

Hank,another option is to change the propellers to a smaller diameter withless pitch, so there is less load on the motor, if you can live with less speed!As Steve said the manufacturer designed it for 120 V & unless you knowall the parameters it's difficult to know what you can get away with.As an illustration of the complexity, a 120V electric raiser isn't as powerful as a 12V cordless drill!Cheers Alan

      From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Wednesday, April 27, 2016 2:08 PM
 Subject: Re: [PSUBS-MAILIST] power converter

Hi Steve,The motors have brushes, so I am going to do a test before I get to concerned.   I can add a battery bank also as you mention to increase the voltage.  I was planning something along that line anyways to increase my range.  I need to add weight to offset the escape pod buoyancy, may as well be batteries.Just a thought, what about running them on AC with a rectifier.Hank 

    On Tuesday, April 26, 2016 7:30 PM, Stephen Fordyce via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Hi Hank,I've dabbled a little bit in (small!) DC converters and my guess is that a converter that will do the current you're after will be expensive/large/complex and probably generate a significant amount of heat.  Also seems like an obscure set of operating conditions that will be hard to find off the shelf.  
You've probably thought about it, but splitting the battery bank and rewiring part of it to supply 120VDC is probably the easiest low-tech solution if you have enough cells to put in series and achieve the higher voltage.  You would get some nice redundancy there too if you have 2 battery banks controlling different thruster sets.
As an aside, I suspect 48VDC is pretty lethal, but 120VDC even more so.
I just saw Alan's email come through - running it off lower voltage is definitely an option, but depends on the sort of motor.  Ie. a brushed motor speed is proportional to the voltage applied (so running at 48VDC would give you less than half speed) - no idea what the Perry ones would be, but being older they may well be brushed.  Brushless motor speed is proportional to frequency applied by the controller.  In both cases torque is proportional to current which is proportional to heat generated.  So the greater the current in your wires, the more heat needs to be dissipated, and if it's not then something will burn out - probably the thin layer of insulation on the motor windings.  The trouble is dissipating the heat from the inner windings (it has to pass through the outer windings, which are producing their own heat) - but like Alan said, if you've got it oil compensated that will help a lot with heat dissipation.  The thermal conductivity of oil is ~6x that of air (and water ~24x air), although the heat transfer is not quite as simple as that.
I'm also pretty sure that the motor will have an inherent resistance that will be designed into it appropriate to the nominal voltage and current, and related to the size of the wires (ie. as Hank pointed out, thinner wires for high voltage as less current is required).  So if you apply less voltage to the same resistance, it will draw less current - ie. I don't think you will be able to get extra current into the motor at lower voltage.  Not quite that simple, but you get the idea.
(that was mostly dredged up from memories of a university subject I did on electric motors a long time ago, feel free to correct me!)

Cheers,Steve
On Wed, Apr 27, 2016 at 10:18 AM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Thanks" Kieth,I started to that but I have no idea if one system is better than another.Hank 

    On Tuesday, April 26, 2016 6:11 PM, k6fee via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Hank,
You want a dc-dc converter, just Google it.
Keith T.

Sent from my Verizon, Samsung Galaxy smartphone
-------- Original message --------From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> Date: 4/26/16 4:53 PM (GMT-08:00) To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> Subject: [PSUBS-MAILIST] power converter 
HELP,,,Turns  out my Perry thrusters are not 36V but 120 Vdc.  I can only manage 48V dc from Gamma's battery bank.  Can I step the voltage up with something.Hank
_______________________________________________
Personal_Submersibles mailing list
Personal_Submersibles at psubs.org
http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles

_______________________________________________
Personal_Submersibles mailing list
Personal_Submersibles at psubs.org
http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles

_______________________________________________
Personal_Submersibles mailing list
Personal_Submersibles at psubs.org
http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles

_______________________________________________
Personal_Submersibles mailing list
Personal_Submersibles at psubs.org
http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.whoweb.com/pipermail/personal_submersibles/attachments/20160427/262efc2d/attachment-0001.html>