How to turn on a 100A load?

rg12

100 kW
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Jul 26, 2014
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I have 10pcs 1500w 5ohm resistors that I will be playing with pretty soon.
Im planning on paralleling them to get 100-180A for short periods but what worries me is the spark when connecting such high load.
Any ideas?
The spark in 60A destroid most gators and XT60's I used...at 100A+ making a connection equals blast, even huge breakers seem that they will spark inside until destroid...
 
What do you mean by 'gators'? sounds like animal abuse..
Have you tried the anti spark XT90 or the anti spark QS8 connectors?

The load when connecting a battery to a controller is not based on the amperage you set in the controller. It's based on voltage, internal resistance of the battery, etc filling up the main capacitors in the controller as fast as possible. Without a resistor somewhere to handle the massive rush of thousands of amps in a millisecond or two, there is a 1000's of amps load which creates the spark.

You don't need 1500w resistors.. try an anti spark connector!
 
A big FET switch would work. If the FETs are fully on or fully off they won't dissipate much. Something like about 5 parallel IRFB4110s would work.

The old-school method is a giant knife switch. Still sparks but can handle it. Where you get a really big spark is when you disconnect it as it will draw an arc.
 
I thought hooking up to a load bank of resistors wouldn't cause a giant bang.

My bad if i thought you were trying to connect an ebike controller..
 
fechter said:
A big FET switch would work. If the FETs are fully on or fully off they won't dissipate much. Something like about 5 parallel IRFB4110s would work.

The old-school method is a giant knife switch. Still sparks but can handle it. Where you get a really big spark is when you disconnect it as it will draw an arc.

My electronics knowledge is kind of limited...
I have the fets but I assume that this is not the only component in the circuit...
 
rg12 said:
I have the fets but I assume that this is not the only component in the circuit...
Search for "fechter" and "anti spark" or "limiter" and you will get a LONG thread that discusses this issue in all detail.
The circuit shown there is quite simple, and uses only the FETs, some resistors, caps and a diode.
 
Since a load resistor isn't capacitive, you don't need to precharge. You can just use a simple FET bank with a 12v supply to power the gates. A SPDT switch toggles the gate between 12v and ground. The wires or resistors may have some inductance, so probably a good idea to use a freewheel diode on the output. For the 12v you need an isolated supply. Just a regular 9V battery would work fine too and last practically forever.

The diode should be rated for the full pack voltage (and a bit more). You can simply use a FET with the gate tied to the source leg as a diode.

 
I read this yesterday, came across it today. Why not do something fancy dancy and have an actuator move the blades of the switch.

A anti-spark XT90 would suffice, or custom antispark.

Another option, get one of those bigass Anderson Power Poles, dremel a bit of the housing out and insert a custom a.s.
 
The anti-spark feature on the XT90s won't help with switching a 100A resistor load. You just need a big metal contact and it will make a spark. Disconnecting the load is where it gets interesting as the contacts will draw a really impressive arc when you open them. If the contacts can open by more than an inch or so, the arc should go out. Otherwise you need a way to blow it out, either magnetic or with air.
 
Chalo said:
Go get you a DC contactor; that's what they're for.

They don't mention the switching voltage, only the coil voltage (the coil is the voltage to turn it on/off right?)

Why wouldn't an anti spark XT90 work?
 
rg12 said:
Why wouldn't an anti spark XT90 work?

I know nothing about anti-spark connectors. But I know they're not a thing you find in industrial equipment.
 
There's a link to a PDF datasheet under the photo that lists the voltage & current capability. I'm not sure what the difference is between SU60 and SU60B is, though. Maybe it means with the blow-out option?

The anti-spark connector won't work as the resistor in those is intended to gradually charge speed controller capacitors. That same resistor is never going to gradually warm up huge load bank. And even when fully warm they would still draw a lot of current when connected to the battery!
 
rg12 said:
Why wouldn't an anti spark XT90 work?

The anti-spark connector has an insulated tip that is fed by a resistor to limit the current to a non-sparking value while the controller caps charge up. Once the caps are precharged, there is practically zero current. The precharge only lasts less than a second.

With a 100A load, the precharge resistor will turn into a rather large ball of plasma as it vaporizes. It would probably make for a good video but your hands may be burned by the blast.

You might look around on Craigslist or eBay for a used service disconnect. You can find new ones at Home Depot or an electrical supply place. A 100A rated one should work for a while and you can resurface the contacts if they get fried. Most have a place for a fuse as well.

 
I would assume a contact voltage rating of 48v dc regardless of coil voltage. For a resistive load, it won't have any problem when the contacts close and when the load is running. The only problem might be when you try to open the contacts it might arc. At 48v, it shouldn't as it is designed for this. At higher voltages, it may or may not sustain an arc. The maximum voltage it can handle also depends somewhat on the current. It can handle more voltage at a lower current.

The dielectric strength is the allowable voltage difference from the contacts to the coil.

My guess is something like these will work OK. 100v would be pushing it, but at anything lower should be fine. If you split the load and used two of these in parallel, you could be pretty sure.

Contactors really made to open 100A 100V loads have magnetic blow outs and are pretty expensive.
Here is a selection of EV contactors:
https://www.electriccarpartscompany.com/Contactors_c_35.html
 
Here's a solid state relay that meets your specs.
https://www.amazon.com/SSR-100A-MGR-1DD220D100-3-32VDC-5-220VDC-5-25mADC/dp/B076GZDXH8

It's cheap, even. I hadn't come across one before with 100A capacity, so I didn't mention it until now.
 
eee291 said:
Chalo said:
Here's a solid state relay that meets your specs.
https://www.amazon.com/SSR-100A-MGR-1DD220D100-3-32VDC-5-220VDC-5-25mADC/dp/B076GZDXH8
It's cheap, even. I hadn't come across one before with 100A capacity, so I didn't mention it until now.

For some reason the Link wasn't showing.
Wow, that is cheap. I've never seen a DC rated one that cheap before. No worries about arcing. It will need a big heat sink for continuous operation, but that should be pretty easy.
 
fechter said:
I would assume a contact voltage rating of 48v dc regardless of coil voltage.

I thought that too, but squinting at the labels in the photos suggests possibly two different voltage ratings, presumably for coil and contacts for each of the 12, 24 & 48V variants. The listing is badly described TBH.


If the SSD Chalo linked to will do the ratings it claims then it looks like a good bet.
 
Ok the link to the listing I posted shows in the photo 12V input 14V output at 200A
So...
Looked for the SSR like Chalo posted on eBay and found this listing for almost half the price:
https://www.ebay.com/itm/162952525681
but while the listing says 100A the photo says 10A (they go from 10A to 100A in different versions) so I sent the seller a message just to make sure it's the 100A.

MEANWHILE, I found the same one in a 120A version but the price is more than double:
https://www.ebay.com/itm/High-Quali...8753be6:g:adUAAOSwSypY9BQn:rk:3:pf:0&LH_BIN=1
 
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