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/diy/ - Do It Yourself

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226578 No.226578[DELETED]  [Reply] [Original]

I've got 4 car batteries hooked into a series. Part of the circuit is a ghetto wire rheostat (sandwiched between bricks). If I try measuring current directly by hooking the multimeter into the series, am I correct to assume that even at the 10 amp setting, it'll fry?

>> No.226580

Oh yeah, I'm trying to limit the current to 3 amps.

>> No.226585

So, is this for heating or suicide?

>> No.226590

Nigga what the fuck you doing with all that power?
you've got 48 volts there. Short-circuit current will be over 200 amps.
The way to determine if you can limit the current to 3 amps is to take your meter on the ohms setting and measure the resistance of your rheostat. Then use ohm's law (V=I*R) to determine how much current would flow. I is current, R is resistance, V is voltage there. So, 48=3R. R=16 ohms. You need 16 ohms there to limit it to 3 amps.

>> No.226593

Making a battery setup for solar charging?

>> No.226596

>>226585
oh bro don't say that... I'm jumpy enough already.

>> No.226599

>>226596
You get much rain where you live?

>> No.226602

>>226599
Dallas. Thunderstorms all last night.

>> No.226639

It's for a heating element, not suicide or solar charging. Good guesses though.

>> No.226652

heating element is a load and will also have resistance. how many ohms is heating element? anus ohms?

>> No.226657

>>226652
Actually that's what this project is trying to figure out. Based on my understanding, the current in a circuit is limited by the portion with the highest resistance? So if the heating element has a resistance higher than my rheostat, the rheostat becomes irrelevant. My rheostat is only a safeguard to ensure that in the event the heating element has lower resistance, current will be limited. I've also got a 200 amp circuit breaker there just in case.

>> No.226665

>>226657
Sort of. In a series circuit, it's the sum of all the resistances. So, the resistor doesn't become irrelevant, it still decreases the current that flows through the heater. But if you were to replace the heater with a short circuit, the current is still limited by that resistor thus protecting against short circuits. But with a high-resistance heater, the resistor is still dropping some of that voltage, and the heater will get hotter without the resistor in there.

>> No.226668

http://www.falstad.com/circuit/
Fool around with this.

>> No.226670

you do not have element yet? Maybe get a couple of them and add in more and more as needed instead of rheostat. sometimes using several smaller ones is done and it works out alright. I have seen some boards use different t stats set to different temps to bring in lag heaters or even timers that will cut off one or two after a certain time giving it extra get up and go during start up for some things.