12v 200+ amp contactor

[bizango]

hello, I have a question about a 12v contactor rated for at least 200amps, perhaps 450 amps. it is a large black cylinder with two large threaded posts (assumed positive) and a single small post near the bottom, the base plate is steel and ground. To test the operation and hookup, no labels on the housing, I used a 7.4v lipo battery, switch, and a light bulb. I hit the switch heard a click and the bulb lights up, so it works!

to test in the operation under load, I hooked it up again with a 48v ebike battery, a 1500 watt speed control 200amp breaker, and bldc motor and switch. turned it on, and pushed the throttle just a little bit. tires move.... immediately I noticed a smell and the body of the connector was getting very hot. I didn't take the time to get a temp reading, and i'm not sure what a dangerously high temp would be. given the low load, I thought it prudent to unhook everything. I noticed the heat remained for some time.

if the connector is activated, it must be hooked up properly right? was I overly concerned without cause? I assume the 12v rating is the issue but it is a little surprising it started heating up so quickly to the point I was worried it might start melting down. what is going on here? how do these connectors work, they use a coil and spring right? why would it get so hot so fast?

I thought the main issue with connectors or switches at higher voltage is the arc causing damage to the internal pads, when the connection is made. beyond this, if the load is small, like a small light, it should be ok. is this wrong? this is why you use anti-spark resistor, to slow the charge across the circuit, for example when capacitors charge. I did not have such a resistor hooked up and assumed with the high amp rating and low load it would be ok. I don't think the connector is necessary for this controller but for a different controller, it will be necessary to understand this properly.


if i have a need for accessories that operate at high voltage but low amps what type of switch is suitable? and is the anti-spark resistor the best way to protect the switch from premature wear?


the picture is not the same unit. mine has three posts was originally purchased for another project from a robotics website.

 

[dominik h]

Have you supplied the coil with 12V.
If you put 48V to the coil you have 16 times more heat and this will kill the coil very fast, even without any current over your contacts

 

[E-HP]

are you using "contactor" and "connector" interchangeably? I can't figure out where the connectors come into play.

 

[Jordan325ic]

I think the best thing to do is post a picture of the label on the actual contactor. This post is fairly confusing as written.

 

[ZeroEm]

He's throwing 48v to the 12v coil.

 

[E-HP]

He's throwing 48v to the 12v coil.

Yup. Seems like a fundamental misunderstanding about how a relay works.
Asking a question about one relay and providing a picture of a totally different one just adds to the confusion, as if the 6 paragraphs didn't achieve that already.

 

[ZeroEm]

It's good that people come here to learn. Should ask before acting. Only problem is with electronics is it has magic smoke in side and should never be let out.

 

[bizango]

Yes I put 48v on a 12v contactor, and yes I became concerned when it heated up so I disconnected it. LOL my bad but no smoke, it just got hot. It was purchased nearly 20 years ago so with no label, so it was worth a shot. Contactors rated to take a 72v battery are expensive, so if anyone would like to recommend one rated for 84v, please do.

I'm not fundamentally confused lol. That would be using a contactor in place of a battery or to brush my teeth. People push their controllers well past rated limits all the time. Perhaps not to this extent so I understand the gentle criticism.

 

[ZeroEm]

I run 72v and always on the look out for higher voltage switches with out selling the house. Not sure volts is the problem, it's when you get into high amps DC equipment get's big and expensive.

Will let you know if I find anything. People always point me to home solar storage but most only go to 48v.

 

[E-HP]

Yes I put 48v on a 12v contactor, and yes I became concerned when it heated up so I disconnected it. LOL my bad but no smoke, it just got hot. It was purchased nearly 20 years ago so with no label, so it was worth a shot. Contactors rated to take a 72v battery are expensive, so if anyone would like to recommend one rated for 84v, please do.

I'm not fundamentally confused lol. That would be using a contactor in place of a battery or to brush my teeth. People push their controllers well past rated limits all the time. Perhaps not to this extent so I understand the gentle criticism.

The "rating" for a relay is usually referring to the contact rating (voltage and current). There are also the control or coil ratings/specs which may or may not be the same are the rated voltage, typically only drawing a 100mA or less.

For automotive relays the contact and coil voltages may be the same, but even then, don't represent the same thing. If a relay is "rated" at 50V 40A, which is 2000W, the relay can switch any combination of signals that don't exceed 2000W; 40V 50A for instance. In your case 12V 200A > 48V 50A. The control/coil rating doesn't change though; still 12V 100mA.

In a nutshell, there are coil specs and contact specs; you have some latitude when applying voltage to the contacts, but not the coil.