Questions from newbie - carbon pile load tester

[kurnia.2]

Hi all,

This is my very 1st day and very 1st post on this site. I'm really excited finding this forum. I've just spent about 2 hrs reading the posts.

I don't have much understanding about electronics. The only thing I know is memorizing the basic formulas. I may not be contributing anything but troublesome posts because my lack of knowledge. I just really want to learn more. Please give me directions.

I have some questions to ask.

What is carbon pile?
How does it work?
What are the applications?
Any relevancies between a carbon pile and a rheostat?


The reason I ask these questions is that I'm into the automotive field. I've seen & used a battery & charging system load tester with carbon pile and I need to own one. Checking the alternator max output is very easy with that equipment. I'm sure most of you know what I'm talking about.

I've browsed my local town & nobody seems to sell it neither know what I'm talking about. I'm in Indonesia by the way. Buying one from abroad will be very expensive.

Is it easy to build? If so, how?


Any recommendations of using a different, easy to use method or equipment to check alternator max output?

Thanks in advance for any directions.


Bob
NB: I'll post another question in different topic on car radio antenna

 

[David Bridgen]

A carbon pile consists of a number of carbon plates or discs held together under pressure in a frame. Their resistance is dependent on the pressure which can be varied with a knob and spring arrangement.

It can be used in exactly the same manner as a rheostat.

 

[kurnia.2]

Thanks again Dave.

I would like to see if I can understand how the system works, then I'll build one. Hopefully I have some luck.

 

[Dean Huster]

A carbon pile is essentially a rheostat, albiet made for very high current and power levels. They're often seen in the automotive industry as variable battery loads for testing the battery. In this application, they're usually spring-loaded so that when the actuating handle is released, the pile returns to its high(er) resistance state. They are not designed to handle the battery load for a long period of time .... just a few seconds, long enough to check the battery for proper operation.

They're big, clunky and imprecise in they can't be reset to the same value repeatedly. Carbon piles were at one time used to vary heater voltage on some old battery-operated tube radios. They were also used to vary the speed of electric fork lifts, although that job has been pretty much been given over to modern power semiconductors.

Dean

 

[ante]

Hi kurnia,

I don’t know if you ever encountered a carbon grain microphone, it works in a similar way. It’s resistance varies with pressure, in this case the pressure from the sound waves.

Dean,

I remember many years ago (pre- SCR) these carbon piles as you mentioned in electric forklifts (very hot). They haven’t used them now for 30 years, even the SCRs is out of the picture. It’s almost all MOSFETs today.

 

[Lenny25]

Hey all, another noob resurrecting an old thread. My first post, so bare with me

I'm building an ac arc welder from old microwave transformers with rewound secondaries (i.e I have stepped the voltage output down and the current up). The secondary circuit (the welding circuit) is producing 27volts, and I have not been able to test the current since i still need to get one of those clamp-on multi-meters. But the machine welds really well, so long as i am welding on something thicker than say 4mm. So it's pretty potent to say the least. I need a way to be able to adjust the amps while keeping the voltage more or less the same. Someone suggested a carbon pile rheostat. I'm struggling to find one though. Any ideas, something i can build that won't cost me the earth?

 

[Reloadron]

Placing a resistance, any resistance be it a carbon pile or big rheostat in series with your transformer secondary will limit the current at the weld, however, it will also cause a subsequent voltage drop at the weld. What you are doing is a basic AC weld and I don't think there is any simple way to maintain the arc voltage and limit the current.

I do have a question though. The 27 volts you are seeing, is that open circuit voltage (no arc) or the actual voltage across the arc (arc voltage) while welding? I am not a welder type but 27 volts across the actual arc while welding seems high to me.

You may want to start a new thread and maybe get some fresh answers. I tend to think there are a few members here who actually weld and built a few home brew welders.

Ron

 

[Lenny25]

When the circuit is open, the volts for each transformer in the secondary windings is around 9v. I experimented with various configurations of transformers to get the best weld.

I can't really remember all the configurations, but I know that two sets of two transformers in series (18v), connected in parallel worked but the arc was very hard to maintain.

Then I tried with a single row of three transformers in series (27v) did'nt seem to work nicely.

Then I tried with two rows of three transformers connected in series, that works really well, gives me a nice arc and is very hot (melts the rod verrrry quickly). So it's great for heavy applications, i just need to tone it down a bit.

To be completely honest, I not completely sure of what effect voltage and amps has on the weld. All I know is that more amps means a hotter and faster weld, and I think one needs a minimum of a certain amount of volts in order to get the electricity to actually jump/arc. Although I could be wrong.

I was worried about the volts dropping and not being able to strike an arc, but something rather obvious that just dawned on me as I am typing now, if i where to use something like a variable inductor or make a coil in the secondary circuit that I can move further or closer to one of the primary coils then the current drop will be inverse to the volts, so the volts will actually increase, which is not really such a big problem ( I think). I wonder what will happen if you have too many volts.

Thanks, I think i will start a new thread. As you can hear I don't know terribly much about electronics, I have just sort of been teaching myself as I go along from forums and websites.