120v DC to 24 or 36v DC step down

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.
thanks,
jess
Reply to
Jess
Loading thread data ...
fork lift or golf cart charger.
Reply to
Edward Heimbach
"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.
Reply to
Leo Lichtman
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.
Reply to
tomcas
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.
Reply to
Ernie Leimkuhler
Thanks Ernie, its probably between 1 to 2 amps. But where is the 120 VDC coming from?
Reply to
tomcas
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.
Bob
Reply to
Bob
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.
Reply to
Leo Lichtman
Here you go, the D-A30-24S will do what you want.
formatting link
for an engineering sample.
Gary
Reply to
Gary Coffman
Maybe one of the big roll around battery chargers that were in so many gas stations that turned into coke and bread stores. Should be some in sales or local flea areas ?!
Martin
Reply to
Martin H. Eastburn
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.
Reply to
Bob
"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 resistor.
Reply to
Leo Lichtman
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......
THANKS
jess
Reply to
Jess

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.