Contactor question

EmVeeTee

10 mW
Joined
Mar 15, 2021
Messages
27
This relates to a IC scooter conversion to electric but I’m thinking this is the best place for this question.

I keep killing my contactor and I am not sure why. Here are the basics of the electrical setup:

4kw 72V hub motor
Kelly sinusoidal controller
72v batter pack that can sustain 150A and peak to 250A

The fully charged pack voltage is 84v. I have fried a couple of Sayoon 72v 200A contactors. I tried a 72v 300A contactor and it stopped working. I also have a 84v 400A contactor.

The contactor has a pre charge resistor and a diode in place for protections.

Is the pack voltage at 84v frying the 72v contactor? Should I focus on the contactor max voltage or make sure it will handle the max peak amps? When it all works it is fantastic but the contactor issue is ongoing. Thanks for any thoughts!
 
Are you trying to go cheap, say too far under $100?

Cheap Chinese need to be very deeply de-rated

by half or more.

I assume you want it to work under load more than just a few dozen cycles?

Mechanical better than SS

TE, Tyco, Potter & Brumfield, Gigavac, Kilovac, Schneider, ABB, Crydom, Crouzet

Vendors like Mouser, Digikey, allied, newark, arrow, element14, avnet
 
EmVeeTee said:
This relates to a IC scooter conversion to electric but I’m thinking this is the best place for this question.

I keep killing my contactor and I am not sure why. Here are the basics of the electrical setup:

4kw 72V hub motor
Kelly sinusoidal controller
72v batter pack that can sustain 150A and peak to 250A

The fully charged pack voltage is 84v. I have fried a couple of Sayoon 72v 200A contactors. I tried a 72v 300A contactor and it stopped working. I also have a 84v 400A contactor.

The contactor has a pre charge resistor and a diode in place for protections.

Is the pack voltage at 84v frying the 72v contactor? Should I focus on the contactor max voltage or make sure it will handle the max peak amps? When it all works it is fantastic but the contactor issue is ongoing. Thanks for any thoughts!
When you say it's a 72V contactor, are you describing the contact voltage rating, or the coil rating? If it's the coil rating, you're probably just frying the coil when your battery is charged up, and need the 84V version. For the example below, the contact voltage is 80V for all versions, but the coil rating is what the description lists:

https://www.aliexpress.com/item/4001113267161.html?af=cicig&cv=buynow&cn=api-xyz1&dp=abv.cicig.co&aff_fcid=4e97eaf92c9f43b8abb05827532b8504-1637966422177-02539-_pyPAvQr&tt=API&aff_fsk=_pyPAvQr&aff_platform=api-new-link-generate&sk=_pyPAvQr&aff_trace_key=4e97eaf92c9f43b8abb05827532b8504-1637966422177-02539-_pyPAvQr&terminal_id=b05273e725e24d088486f99b0e79ffe7
 
This is the type I have been buying: https://www.aliexpress.com/item/1005003605345485.html

When I say 72V or 84V, it is the coil rating. Across all of this type/brand of contactor, the contact voltage is stated as <= 80V

I haven't intentionally gone cheap. This contactor is often recommended by the controller manufacturer. I think my battery spec is just pushing too much power for this tier of contactor.
 
EmVeeTee said:
This is the type I have been buying: https://www.aliexpress.com/item/1005003605345485.html

When I say 72V or 84V, it is the coil rating. Across all of this type/brand of contactor, the contact voltage is stated as <= 80V

I haven't intentionally gone cheap. This contactor is often recommended by the controller manufacturer. I think my battery spec is just pushing too much power for this tier of contactor.
I think rated voltage means rated voltage in this case. It's not nominal voltage like for a bike battery; so when you fully charge your battery to 84V (20S, assuming lithium ion), you're exceeding the 72V rating by ~17%.
 
Thank you for the comments. I'll wire up the 84V 400A version that I have and give that a go. It is quite a bit bigger physically so I just need to modify my mounting plate.

@john61ct - are you suggesting something like a 120V coil might be worth exploring with these Chinese contactors?
 
Going much higher in DC voltage capacity rating cannot hurt.

Certainly make sure to ignore the AC rating completely.

But the ampacity maximum stated is what is particularly suspect.

Testing a few hundred cycles to destruction would give the real answer

but then many cheap-Chinese can't be relied upon to be consistent from one year to the next

even from one production run to the next.

So IMO really, buying a known good Western-brand product from a trusted vendor is worth even 5x the cost.

These type if components should not be purchased through open marketplaces.

Although I have had great luck with eBay +PayPal, even secondhand industrial sources

sometimes the older it is, the better
 
So what is the benefit of mechanical (at the cost of several watt/h) vs. solid state?
 
The FET based units at such high power use cases are just not as reliable robust, long-lived

cheap Chinese versions even more unrealistically rated.

I would love to be proven wrong.
 
john61ct said:
The FET based units at such high power use cases are just not as reliable robust, long-lived

cheap Chinese versions even more unrealistically rated.

I would love to be proven wrong.

Are there any links to FET based units? I've never seen one.

But, there is already a FET based "contactor" on every E-bike, it's the battery BMS. :mrgreen: No?
 
I'm now looking at a Gigavac GX11-HA or GX12-HA. Here are the specs for each:

GX11-HA
Coil Voltage Nominal - 72VDC
Coil Voltage Max - 96VDC
Contact Current Continuous - 150A
Contact Current Max - 225A

GX12-HA
Coil Voltage Nominal - 72VDC
Coil Voltage Max - 96VDC
Contact Current Continuous - 225A
Contact Current Max - 350A

I'm leaning towards the GX12-HA which should provide the headroom that I need on power surges. Gigavac notes that you do not need/want to use a diode on this contactor.

Anyone have experience with these? Thoughts on this contactor for my application? A good pre-charge resistor to use with this and a Kelly Controller?
 
EmVeeTee said:
I'm leaning towards the GX12-HA which should provide the headroom that I need on power surges. Gigavac notes that you do not need/want to use a diode on this contactor.

It seems that you're using this for protection, not just as an on/off switch, and in addition to your BMS. What components are you trying to protect?
 
You might want dissect one of the failed ones to see what exactly failed. If the contacts are fried, possibly your precharge circuit isn't working. If the coil is going open, then it is probably running at too high a voltage.
 
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