Like the thought but to much work!
For the record! If the PWM circuit is followed by a capacitor bank the voltage
is in fact the averaged voltage of the output from the PWM. The final
capacitors and the motor work as a LC circuit and the values of the two
average the voltage over a set time. It is fair to say that the controller has
such a circuit within the box to average the voltage. Theory says that the
voltage of a PWM circuit is in fact the input voltage but in a controller it
has likely been conditioned to show the voltage based on time.
About the Mosfets. They are cheap as components. The drive circuit offers the
right voltage to the gate. I would not series connect two controllers to offer
higher voltages to the motor. This is based on the LC design stated above. I
would not parallel connect two controllers to increase current.
This is what I would do:
I would get a controller that will handle the voltage you desire making sure
it used fets as the final stage in the controller.
I would open the box and get the part numbers of the fets within.
I would then go online to order more fets but first I would download the fet
data sheet.
The data sheet offers the voltage they are rated at, gate voltage, and
amperage designed to switch.
Because fets are voltage switched not current switched all you need is the
correct switching voltage and small drive circuits will drive many fets.
fets don't need circuits to balance load to them because unlike transistors
thermal runaway is not a problem with them. It is important that all fets are
the same type but that is not a problem if you order all the same fets as
those inside the box. If the circuit was never going to be mechanically tested
you could use heavy gauge wire as a buss and connect them together off the
board. Because boats go through harsh and brutal conditions they can be
breadboarded and installed in another box that has good heat sinking like an
old inverter case or such.
You can change the amperage rating of your controller with components
assembled in another box. You can't change the voltage rating in the same
fashion because the components were not designed for a higher voltage. It is
true that the components are typically rated at twice the designed voltage of
the equipment, but all voltage dividing circuits on board would have to be
rebuilt to feed all the components and that is to much work.
I have done the work on my solar install. It works without a hitch. My 30A
controllers are now 60A controllers. To review: fets can be paralleled but I
would not do that using more than one controller. The reason that is true is
the control part of the circuit will likely not play fair in parallel. For
this reason use the controller to control a set of paralleled fets of the same
value as the control was designed to control.
Disclaimer: This post is for information only. Just because it can be done,
and I supplied information on doing it, is not a guaranty it will work for
you. For this reason You must take all responsibility for your experiment and
by doing this job, you and your family will not hold me, or mine, responsible
in any way. You must understand that the voltages stored in capacitors can
cause great bodily harm or death even at lower voltages than you will be
working with. As a hobby we do some very dangerous things and blame no one but
ourselves for the outcomes. This would be considered such a thing.
Kevin
On Friday, July 04, 2014 09:59:34 PM you wrote:
> Art,
>
> Great questions (parallel controllers? serial controllers?)
>
>
> One concern with serial-ing two or more motor controllers: grounding. The
> controller of the higher voltage band would not use the same Gnd, probably
> making the case "hot" in terms of being 36v or 48v above boat ground or
> traction battery ground or motor ground or dock ground or water ground.
> There are likely more concerns.
>
> I thought parallel-ing would work until JamesCook? pointed out some
> balancing/feedback challenges.
>
> Additionally, it is not just the Amperage rating of equipment that deserves
> heeding; higher voltage requires thicker insulation and greater clearance
> between circuits on Printed Circuit Boards and almost all their individual
> components. Higher voltage jumps gaps easier, regardless of the Amperage
> or width of the river of electrons. All those internal components are
> rated to maintain their integrity in both net speed (voltage) and volume
> (amperage) of electrons. Exceed those ratings to get a one-time peak at
> the magic smoke.
>
> Mark Stafford
Posted by: pembertonkevin@gmail.com
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