Looking for an adapter or step down transformer from 120v DC down to 24 or
36v DC. If anyone knows of someone who carries these I would appreciate a
note and or a URL.
It is so I can run my ReadyWelder off my strictly DC SA200 without having to
find a 110v AC plug in or use a generator or use batteries.
"Edward Heimbach" wrote: fork lift or golf cart charger.
The OP wants to work from a 120v DC source. Your typical battery charger
requires AC. Since there are no transformers for DC, this is not an easy
problem to solve. A dropping resistor would waste a huge amount of power.
It might be possible to build a solid-state device that converts DC to AC,
steps the voltage down, and then rectify, but that seems like a LOT of
trouble and expense. The simplest idea I can think of would be a DC motor
driving a DC generator. Maybe you could couple a universal motor from a
power tool, like a saw, to an automotive alternator.
I got to ask- what is the source of the 120 volts direct current? What
you are looking for is an inverter. The price is a basically a function
of the current capacity, which in the case of a welder is going to be
relatively high and relatively expensive.
All he needs to power is the 24 -36 volts for the wire feed motor in
the Readywelder spoolgun.
It is a very small motor, about the size of a film-can.
If you could rig up a micro motor generator that would be fine.
Maybe the alternator from a really small 4 cycle engine coupled to a
little 1/16" HP motor.
The 120VDC power is generated in the exciter generator. That's the small
generator that sticks out of the front of the machine. It supplies power to
the receptacle as well as excitation voltage for the main welding generator.
In an earlier post I objected to using a dropping resistor because I thought
we we dealing with the welding current. If, as Ernie says, you only need to
deal with 1 or 2 amps to a tiny motor, I think a dropping resistor would be
do-able, and certainly simpler than an alternator.
(120v - 36v) x 2 amps = 168 watts. This could be done by tailoring an
electric heater coil.
A dropping resistor would work very well indeed as long as the load remains
constant. I don't have the technical information for the ready welder, but I
suspect that the load will be greatly reduced when the trigger is released.
When the trigger is released the wire drive motor will stop, but the control
circuit will likely remain powered in a sort of stand-by mode and the load
will probably be reduced from about 2 amps to maybe .5 amps. According to
Ohms law a 45 ohm resistor would be required for a 90V drop with a 2 amp
load applied. [(120V-30V = 90V drop) / 2A = 45 ohms]. If that same 45 ohm
resistor were used for a .5 amp load, the voltage drop would be only 22.5
Volts. [ .5 amps X 45 ohms = 22.5 Volt drop] This would leave 97.5 Volts
[120V - 22.5 V drop = 97.5V] applied to the control circuit, which may be
enough to cause damage.
"Bob" wrote: (clip) I suspect that the load will be greatly reduced when
the trigger is released.(clip)This would leave 97.5 Volts(clip) which may be
enough to cause damage.
I was assuming that Ernie's statement meant that the drive current to a
small motor was going to be switched on and off. If your suspicion is
correct, then I can see the problem. I can also see a solution: add a
relay or other switch to add more resistance when the circuit goes to
"standby," and the motor is off. If a very low standby current is needed,
it might be smarter to use a voltage divider rather than a dropping
I want to thank everyone who added their input on this subject. I will
definitly look into your suggestions......as a matter of economics, I don't
want to add another 3 or 400.00 to the price of getting this going on top of
what I paid for the welder. Again......