100A Contactor Burned on First Try

R

rg12

100 kW
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Jul 26, 2014
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Bought this 12V 100A contactor from eBay, I thought that the voltage is just for the coil (to turn it on) so I connected a 100V DC with 80A of load and connected the contactor to a 12V input, then it turned on and my amp meter reads 80A (all good so far), turned it off by removing the 12V from the contactor and suddenly I hear a khhhhhh sound and smoke came out of the contactor.
I thought the only thing that matters is the current which I didn't exceed but it sounded like an arching inside when I turned the contactor off.
Will that suite my 100V?
https://www.aliexpress.com/item/33021723308.html?spm=a2g0o.productlist.0.0.736a607avb44pf&algo_pvid=268d56c6-95ec-411b-a179-dea8e3c73cd5&algo_expid=268d56c6-95ec-411b-a179-dea8e3c73cd5-0&btsid=e72f36fc-e8e6-4406-ad6c-e02da025b9e9&ws_ab_test=searchweb0_0,searchweb201602_6,searchweb201603_52

It's rated for 72V (I believe lead acid battery nominal) but will I have to turn the contactor on by connecting 72V to it?
I want to control it with a 12V and have it handle 80A at 100V DC.
 
G'day rg, maybe I can help.
Was the contactor rating DC or AC? The way they switch can be different. DC switches "snap" open quickly to kill the arc while AC switches open more slowly to let the reversing current quench the arc. Take a look at those old style "scissor" or "blade" type switches used for high voltages. An AC switch slides the contacts apart but a DC switch has sprung contacts that snap apart. Also, if your contactor was rated for switching 12v, it may not open the contact far enough apart to quench the arc.
Hope I've made sense.

AussieRider
 
Eaton, Bussman Cooper, Blue Sea

Cheap Chinese from random suppliers are never appropriate for critical use.

Ratings are shall we say, "optimistic"
 
rg12 said:
I thought the only thing that matters is the current which I didn't exceed but it sounded like an arching inside when I turned the contactor off.
Will that suite my 100V?
Click to expand...

As AussieRider says, breaking DC is difficult due to arcing across the contacts as they open. It sounds like this happened to your contactor despite using it in accordance with the seller's claims. Unfortunately this would mean it is not suitable for the voltage & current claimed by the seller, despite them saying it's suitable for vehicle use up to 120V.

Looking more closely at the spec, the fault current it can break is given as 800A/5ms @ 48VDC, which seems pretty weak for a batter application. I don't know what interupt rating is typical for DC breakers, but your household AC breakers are rated for tens or hundreds of thousands of amps.
 
But you didn't address my main question if the rating is both for the main current or just for the coil?
 
What you seek does not exist for cheap, unless on eBay when you know the exact part# you're looking for and are patient

Look through and read how to use the specs here:
https://www.google.com/search?q=site%3Awww.electriccarpartscompany.com+contactor

For even quality makers, if you need 100A, then buy gear rated for 150A.

For cheap chinese stuff, if you need 100A in reality, you need to go to at least 300A maybe 500.


 
Coil and contact ratings are 2 separate things. The coil part is usually marked separately, and on good contactors is actually swappable unit. They can also be AC or DC.

The one you listed at the top appears to be a 24V coil in the picture but you can select 12V, 24, 48, 72, etc
 
dustNbone said:
Coil and contact ratings are 2 separate things. The coil part is usually marked separately, and on good contactors is actually swappable unit. They can also be AC or DC.

The one you listed at the top appears to be a 24V coil in the picture but you can select 12V, 24, 48, 72, etc
Click to expand...

The coil is the "trigger" voltage right?
How do you know that they mean that it's the coil voltage? it doesn't say in the listing...
Would the contactor be different if it was built for 12V DC or 100V DC but same amp rating?
 
rg12 said:
Would the contactor be different if it was built for 12V DC or 100V DC but same amp rating?
Click to expand...



Yes

Good luck finding a 100V 100A dc contactor that is affordable. Even then you really will need a pre charge circuit to keep the contacts from welding themselves shut when energizing.
 
Lower voltages in DC are **more** stressful, so need even greater "overkill" wrt ratings. they generally are designing for the upper parts of the quoted range.

With cheap Chinese, best approach is order a bunch of different overkill-rated ones, then actually test.

But then inconsistencies from one batch to the next can sabotage you.

Much better to order from Mouser, Digikey or Newark/Element14 in the first place, can inspect detailed data sheets you can (mostly) trust before ordering.
 
The coil voltage is for your low-current relay "signal" to control the main contactor closing (connecting). That is the voltage chosen, 12/24 etc.

The contactor spec is for the high current (way above) the actual power being connected / isolated, and voltage very widely specified if at all.

So if you applied a high current to the coil, that likely fried it. Especially if the voltage applied was higher than the coil voltage you ordered.
 
Is there any reason not to use a solid state relay (SSR) on an Ebike? How well do they handle the inrush of a controller and disconnecting high loads? Better than contacts?

For example this one is $41, looks OK for "normal" requirements, but light for the posters stated requirements:

AD-SSR6M40-DC-200D

Crydom makes a sufficient rated one, but more like $150:

DC100D100

Might find something in the middle. For a mechanical contactor, I would suggest a Gigavac:

GV200-MA

Make sure you get the 12/24 coil with economizer. Uses about 1/2 the current to hold closed. The previously mentioned Tyco EV200 is also a good choice. It also has the coil economizer option, normally the default.
 
john61ct said:
So if you applied a high current to the coil, that likely fried it. Especially if the voltage applied was higher than the coil voltage you ordered.
Click to expand...

You can't "apply" a higher current to the coil, it draws what it draws just like any other inductive load.

There is a voltage range however, too low and you don't pull hard enough to overcome the spring, possibly leading to arcing if you manage to get them "almost" closed.

Too much voltage and you'll overheat and burn out the coil, and it will let go when it can't pull hard enough to overcome the spring any more.

As for an SSR, their enemy is mainly heat. They're a semiconductor, and therefore get pretty hot when being run near their ratings. Too long running hot and like any other semiconductor their resistance increases making them run hotter still, and you can guess how it ends. Maybe with some considerable heat sinks they'd be OK if you over rated them enough.
 
The contactor listed by the OP comes with your choice of a 12/24/48/72V coil. Selectable in the venerable "Color" option on AliExpress. He was pretty clear he used 12V on the coil, which wouldn't likely smoke any of those choices.

Do you think the heat generated by an SSR would be worse than the traditional pass through BMS boards? Isn't it really a standalone version of the same switching circuit in a pack BMS. The SSR a UL rated industrial device would seem on the surface more likely to be more robust? Rated for peak requirements, it would be coasting at 1/4 to 1/2 the rating normally.

I've been discussing the possibility of using an Orion BMS in my build. It's the BMS I've used several times in off grid energy storage applications. It would need an external battery disconnect switch/contactor. In an email discussion with the engineer his concern was MOSFET/FET's usually fail ON. Which defeats the protection circuit.
 
Yes, pretty sure everything fails On (closed), since the usual mode is that contact points weld together.

That's why pre-charging helps, anything that reduces spark-pitting.

SSR are **not** longer lasting, more reliable than mechanical contactors costing hundreds of dollars.

And cheap-chinese ones are much more "variable" in how well designed, built, QA-reject or counterfeit components, just like cheap BMSs.

Sure good quality SSRs can be found, buying from Mouser et al, but still for longevity need to be oversized and regularly tested, bad batches sneak through even with top-notch western makers, just **far** less frequently.

And everyone should realize in regular use, these components do wear out over time, should regularly be replaced, do not believe "millions of cycles" ratings under heavy-amp loads.

For high reliability, double up, two units must close to pass current. But then need a warning when the first fails, or regular test/inspections,
 
I agree periodic testing is a terrific idea. I sort of see that as the Achilles heel of shrink wrapped and especially potted battery packs without some sort of test function. If you are building your own pack, a switch with a resistor can be placed across the voltage sense wires of one cell to simulate a low voltage disconnect.
 
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