Relay for up to 100V DC?

[rg12]

I have this load tester with 5 units of 5ohm 1500w resistors.
I connect and disconnect manually to change current draw and want to connect all 5 to 5 relays and have 5 switches to increase the current with.
I'm using it with batteries up to 100V (24S).
So I have about 15A in average and 20A max at 100V for each resistor of 5ohm.
There are plenty of cheap relay boards on eBay like this one:
https://www.ebay.com/itm/250V-30A-4...836625?hash=item3b1ce4f1d1:g:kNYAAOSwZ2BbpVPO
That go up to 30A but they are all rated 250V while if you look at the relay itself it says 250VAC/30VDC
Do you think I will fry it at 100V from a battery?

 

[billvon]

That go up to 30A but they are all rated 250V while if you look at the relay itself it says 250VAC/30VDC
Do you think I will fry it at 100V from a battery?

Yes. It will arc if you try to switch it under load.

 

[rg12]

That go up to 30A but they are all rated 250V while if you look at the relay itself it says 250VAC/30VDC
Do you think I will fry it at 100V from a battery?

Yes. It will arc if you try to switch it under load.

Damn...
Any solution from eBay without going to digikey and ordering a single relay that will come without a pcb?

 

[billvon]

Damn...
Any solution from eBay without going to digikey and ordering a single relay that will come without a pcb?

If they are resistive loads, just use MOSFETs. They are cheap and easy to use. You can get a 120V, 60A MOSFET for about $1.50. You can drive them with TTL signals (0-5V)

If you really want an assembled thing, use a DC SSR. They are a LOT more expensive ($50 or so) but they can be connected with no other parts. A 200V 40A DC SSR is about $50 and comes with screw terminals.

 

[rg12]

Damn...
Any solution from eBay without going to digikey and ordering a single relay that will come without a pcb?

If they are resistive loads, just use MOSFETs. They are cheap and easy to use. You can get a 120V, 60A MOSFET for about $1.50. You can drive them with TTL signals (0-5V)

If you really want an assembled thing, use a DC SSR. They are a LOT more expensive ($50 or so) but they can be connected with no other parts. A 200V 40A DC SSR is about $50 and comes with screw terminals.

Found this for $7.5 shipped
https://www.ebay.com/itm/DD220D40-S...sh=item3b3da6c20d:g:PCMAAOSw-mVd4PtQ&LH_BIN=1
It's rated for 40A and 220VDC which I doubt chinese ratings but I will run it at about 15-18A 70-100VDC
About less than half it's ratings...
Do you think I will need a heat sink for it?

 

[Bikegirl]

I used a zeva contactor and precharger for a 72v system, works well with a cheap ass reducer giving 12v for the start system, and rated dc circuit breakers.

https://www.zeva.com.au › ...
Smart Precharger - Zero Emission Vehicles Australia

https://www.zeva.com.au › ...
Gigavac P195 Minitactor - Zero Emission Vehicles Australia

AU $20.59 | Step down Transformer Electric DC Converter Adapter 48V 72V 96V TO 12V 10A USB 5V
https://a.aliexpress.com/NsYpON0G

Sent from my SM-G950F using Tapatalk

 

[markz]

Buying from Fleabay, I'd want 200Vdc and 40A for the sellers specifications, as they would be over exaggerated.

 

[rg12]

Buying from Fleabay, I'd want 200Vdc and 40A for the sellers specifications, as they would be over exaggerated.

That's exactly what I posted, 220VDC, 40A and I'm using less than half.

 

[john61ct]

eBay sells robust contactors from Gigavac, Kilovac, Tyco, Schneider, ABB, Crydom, Crouzet

not just the poorly spec'd Chinese SS stuff

 

[rg12]

eBay sells robust contactors from Gigavac, Kilovac, Tyco, Schneider, ABB, Crydom, Crouzet

not just the poorly spec'd Chinese SS stuff

These brands are expensive especially when I need 5pcs.
I rather buy a chinese one and use half it's specs for $7 than buy 5pcs $70 brand contactors

 

[john61ct]

Sure, not reco'ing for you specifically, just pointing out eBay is good for higher quality as well.

I've been collecting top notch DC contactors 200A many 500A, for an average of about $15 each.

One dud out of a dozen so far, and eBay refunded me in under 48hrs even though the seller tried to state "as is".

 

[markz]

Sure, not reco'ing for you specifically, just pointing out eBay is good for higher quality as well.

I've been collecting top notch DC contactors 200A many 500A, for an average of about $15 each.

One dud out of a dozen so far, and eBay refunded me in under 48hrs even though the seller tried to state "as is".

That is a good run for dud ratio.

The AS-IS gotta laugh at that, I guess they are trying to take a jab at the buyers who are new(er) to ebay and dont know the rules precisely.

 

[danielrlee]

Sure, not reco'ing for you specifically, just pointing out eBay is good for higher quality as well.

I've been collecting top notch DC contactors 200A many 500A, for an average of about $15 each.

One dud out of a dozen so far, and eBay refunded me in under 48hrs even though the seller tried to state "as is".

That is a good run for dud ratio.

The AS-IS gotta laugh at that, I guess they are trying to take a jab at the buyers who are new(er) to ebay and dont know the rules precisely.

On eBay, "as is" is a fair declaration if the condition is specified as 'faulty or suitable for spares'. 'New' or 'used' condition means that the item must be "fully functional".

EBay policy states that buyers are not covered by the 'money back guarantee' for 'not as described' cases where the item condition is specified as 'faulty or suitable for spares'. In practice though, eBay often ignores its own policy on such matters.

 

[john61ct]

Yes those three options for condition is what rules for not as described.

Only "Not Working Parts Only" status removes warranty protection.

Writing As Is or No Returns is just a bluff if posted as Used.

But be careful about Local Pickup, that can hurt warranty claim, some say must be shipped by the seller

 

[markz]

Thats why I see some sellers always put down "For Repairs" so they got a bigger lee-way on the sellers part.
Overall ebay is on the buyers side if everything is truthful and honest.

 

[john61ct]

To the point it would be easy for a buyer to scam the sellers.

With great power comes responsibility, don't abuse it or they'll take it away.