lowering dc voltage to drives?

[KEYTEEM]

I have finished a power supply that is going to be used for rutex drives
and my next step is to test+tune the motors without being hooked up to
any mechanicals , the output of the supply is 86v and the instructions say
to use a lower voltage at first,"even 24v will work",.
Can anyone suggest a way to lower the voltage from my supply ,for temp purposes, so I don't have to build/buy another supply.
Inline resistor from supply to drives?





Thanx Den

[vladdy]

you could always try a couple of car batteries [in series], or even borrow a couple of battery chargers, or old pc power supplies..??

just a thought..

enjoy..

[GrantM]

A resistor is not the way to go, it would likely dissipate too much power for a start, not to mention other problems.

Are you using steppers or DC servos?

If DC servos, then assuming it's only supplying the motor (ie. the drive electronics itself has it's own supply), then you could likely get away with just about anything for an inital setup/trial, providing it has sufficient current capacity.

The speed would be limited of course, depending on the motor you're running (RPM/V and drive duty cycle), but as Vladdy suggested, 2 car batteries in series would do (even one may do for a basic trial).

Couple of points though - Car batteries can generate huge (dangerous) currents, so ensure you put a fuse or circuit breaker in the line from the battery, just in case you mucked something up. Fuse/breaker rating should be on the low side for initial testing, no more the motor max current. Battery charges may not work for a number of reasons, some may, some wont, many electronic style ones won't.

Ensure the motor you are using is suitably matched with the suppy voltage you intend using long term (ie. 86V).

[smarbaga]

hello
if you are using a linear power supply ( stepdown transformer )
try to find a power stat, the type that plugs into the wall and has
a wall type of plug on the output with a 0-140 volt knob on the top.
these are usually are good for 8 to 10 amps.
meter your output and bring the dial up untill the desired output is
reached, good luck.

[KEYTEEM]

Yeah I was thinking of batteries but don't have any, and after thinking about a voltage divider resistor setup
just ain't worth setting up, and i have tons of time into this project any how so a little more to do it by the book
seems the way to go, a power stat sounds like it might work but don't have one so,

I'm gonna hack up a line printer I have and use it's power supply, didn't
want to hack it up but have already needed to have one for this project
more than once so chop chop.

Thanx

[vtxstar]

Another choice is a DC to DC converter but unless you have one laying around that will fit the supply you built, you will have to buy one - thus not meeting your initial request.

Is this a classic supply with a bridge rectifier on the secondary of a transformer? If so, did your transformer have other secondary windings?

I'd go with the battery option. As mentioned make sure you fuse it properly or something dramatic could occur.

[GrantM]

You can't pinch the battery out of your car for an hour or two perhaps? (be careful of the radio code!) You didn't mention if it's a DC servo or a Stepper, but still assuming servo, you could also try a Cordless drill battery, but just watch the heating of it. You don't want to overload it.

The Powerstat that smarbarga mentioned is also known as a Variac (I think that's what he's talking about), though you will find a lot of them are only good for about 2 amps. Biggers ones are around (mine for example is good for about 8 or 9 amps), but they are very expensive generally.
The big thing with a Variac is that they are an Autotransformer - and that also means they are NOT AN ISOLATING TRANSFORMER. That may not be so bad in the US where they use lower mains voltage, but it's still potentially very dangerous, especially if you're not experienced. It simple terms it means that one of the wires on your 'low voltage' side is connected directly to one of the mains wires, so it's not quite the nice safe low voltage you might think it is.


As we don't know what the specs of your motor are, it's a bit hard to advise you, perhaps you could let us know.

[KEYTEEM]

Sorry it's a dc servo setup , typical transformer/bridge/cap .
I removed a power supply from a line printer last night and am gonna use
it too test the motors with and it should work fine