dc motor

jake

Will this work?  I'm thinking of using 9, 250 watt solar panels in 3 strings to get 90 volt dc and direct connecting a  dc motor to a  belted refrigeration compressor with an electric clutch, I would allow the motor to free wheel until the motor reached a predetermined speed and then engage the electric clutch. The refrigeration system would make ice to cool the cooler when there is no sunlight. I am refrigeration tech and can do all the calculations on sizing etc., I lack the solar knowledge.

Dave Angelini

What happens when the sun does not shine?  You really need a battery,
 but there are ways to do this if you do not care about if the sun is shining.

BB.

Yes--It is possible. These days, there are some installations that use a standard 3 phase motor and a VFD (Variable Frequency Drive) setup for direct connection to solar power.

Could work very nicely for your needs (and you may not need the clutch--VFD does "soft start" and high torque for starting). However, you will still be on the "leading edge" technology (we sometimes call this the "bleeding edge"). It should work well, providing you can find a good VFD for your needs and a knowledgeable support/sales company.

Here is some background on water pumping usage of this tech:

WELL PUMP and Inverter QUESTION
Wind/solar for large scale pumping etc (out of my depth!)
could use knowledge - using Gould jet pump - transfering from 230vAC to ? DC (new link/thread 10/27/2012)
Help required to design off grid system (information on possibilities to connect "standard VFDs direct to solar panels) (new link 1/13/2013)

-Bill

Dave Angelini

Wow "these days" a DC motor on a VFD. Who would have dreamed it?

BB.

Actually I said a 3phase motor on a VFD... 3 Phase motors are (I would guess) cheaper/easier to get vs other DC type motors.

But the wide variation in what is a "DC Motor", it is possible that some variation of VFD (DC Servo Controller) can power a DC "Servo" Motor. (I.e., a "brushless" DC motor).

Don't claim to be an expert--Just suggesting paths for further investigations.

A VFD+3 phase motor (or DC servo motor) is usually a "better solution" vs a traditional series or shunt would DC motor (aka "brushed" motor or universal motor). While brushed motors have been used for a 100+ years--Typically the brushes will not last more than a few (to 6?) months before needing replacement (in a typical near 24 hour per day operation)--In my humble opinion.

VFDs are (potentially) very nice because they can adjust the RPM of the 3 phase motor based on power available from the solar array... For example, the VFD driven motor simply slows down during less than ideal sunlight--Instead of stalling/shutting down with less than ideal solar radiation (or having to oversize the solar array to provide "enough" power towards the beginning and end of day).

-Bill

Dave Angelini

I was just thinking of my old belt drive refrigeration on my sailboat and if the DC motor the OP has is anything like that I would be impressed if it could be done another way that was reliable. He probably needs a battery unless he is going to not need to need to run this reliably is my point. I am confused at why he needs 90vdc?

BB.

I have seen 90vdc motors in times past (as I recall).

-Bill

Dave Angelini

Well not 90vdc on a sailboat for sure. Maybe he will grace our efforts here and respond? maybe not...
So how the heck are you Bill?

Johann

Most of our DC motors are 90 volt DC with a permanent magnet, we also have some with an field winding or 4 to 6 wire DC motors.
We set them up with an electronic drive either for speed mode or torque mode as needed for an application.

DC motors are not maintenance friendly at all and we are replacing them with 3 phase motors that last 5 times longer without having to touch them. No more arcs that those DC motors have that can interfere with many electronics, no more special wiring and components in order to  kill that arc and interference that usually take out other electronic items or make them run absurd  and no more brushes...........yes, life is good.
 

Dave Angelini

AC appliances always outlasted the DC ones also. On a boat the AC electronics for the inverter were an issue because of lightning and so DC had it's advantages. There is always good news and bad. The VFD electronics can radiate a nice field. When I walk near a water tank with a Grundfos running inside my AM radio cuts out.