Heavy duty DC relay needed

[wmgeorge]

A starter solenoid from a car or truck will work, they are meant to switch a 100 amps or so DC. I think one from a older Ford will work as they are not mounted on the starter. Use a resistor to drop the coil 24 volts to 12, trial and error and a ohm meter would help.

 

[GLC]

A starter solenoid from a car or truck will work, they are meant to switch a 100 amps or so DC. I think one from a older Ford will work as they are not mounted on the starter. Use a resistor to drop the coil 24 volts to 12, trial and error and a ohm meter would help.

I burned up a few auto and diesel solenoids, They would just get hot and melt. I got everything up and running now.

 

[Ampster]

I burned up a few auto and diesel solenoids,

Yes, they are not designed for continuous use. A Kilovac with energy saving coil would work in continuous use

 

[A.Justice]

A starter solenoid from a car or truck will work, they are meant to switch a 100 amps or so DC. I think one from a older Ford will work as they are not mounted on the starter. Use a resistor to drop the coil 24 volts to 12, trial and error and a ohm meter would help.

The OEM solenoid on my Ranger that only has 30k miles is already dead / dying. I wouldn't recommend an older Ford solenoid.

 

[BruceM]

Ampster raised a good point on the typical failure of DC SSRs of ON. Relays do occasionally fail with welded contacts, but I expect that the $25 EV relays rated for 900V that A.Justice linked to at BatteryHookup.com would be so overkill for this application that that would never happen.

I like Sunshine's PV shorting method via SSR (solid state DC relay. It has real merit for dedicated PV for water heater load; failure mode is PV off, thus the simplest setup. It's probably my preferred choice. It would also work nicely for 120V or 230V element, with 4 or 8 24V panels in series. For direct 120VDC use,hot weather performance with 4, 24V panels in series is going to suffer but 5 in series is going to be a bit much for cold weather based on my testing. Using 4/8 panels for 120/230V is the simplest.

 

[GLC]

Like I said previously, I did wind up fixing the problem with a little tweaking. I used the relay below. I had to increase the spring pressure where the points disconnect. Then I had to increase the distance of the points so the dreaded green/blue flame would extinguish. By increasing the travel between the the contact points. I have not had an issue since I installed it in May. Everything is working well.

https://www.amazon.com/dp/B07FCKLMNB?psc=1&ref=ppx_yo2ov_dt_b_product_details

 

[Vigo]

As much as i love a problem that's already solved.. just wanted to add, the 'appropriate' version of the starter solenoid mentioned earlier, is a solenoid from an older ~36-48v golf cart before the era of solid state speed controllers. Using 'continuous duty' as a search term while looking for something like that could also help. Plenty of '36 volt dc continuous duty solenoids' of 100a capacity out there when you look at golf cart parts.

 

[BradCagle]

These are great, and only use 1.7w since it has a built-in economizer.

TE Connectivity EV200AAANA 500a 0-900vdc Tyco 12/24v

These were recovered from EV battery modules. These are VERY EXPENSIVE online. If you have any project that needs a high current relay this is your chance to save some money. Make a cheap 30a BMS into a 500a BMS. This will work for batteries in the 9-36v range so perfect for Lifepo4 and Lithium...

batteryhookup.com

 

[GSXR1000]

mount this to the side of your tank and no electronics and no parasite power consumption

 

[Ampster]

mount this to the side of your tank and no electronics and no parasite power consumption

Are the contacts rated for DC?

 

[GSXR1000]

Are the contacts rated for DC?

it is a bimetalic switch.... so technically no because it is for a 30 amp 240 vac appliance. like is that copper wire rated for DC it doesn't care

 

[Ampster]

it is a bimetalic switch.... so technically no because it is for a 30 amp 240 vac appliance. like is that copper wire rated for DC it doesn't care

Bimetalic means it is a lamination of two different metals that expand at different rates based on temperature. That works fine for AC as the gap gets closer and closer but doesn't work for DC. It works fine for AC because 60 times a second the AC voltage goes to zero so if there is an arc it is very short. With DC the arc could persist for several seconds. DC switches are designed differently with bigger gaps and with mechanisms that snap closed and do not increment like the bimetalic thermostat switch in an AC water heater..
The wire doesn't care if it has DC or AC because it is not a switch.

 

[Eber]

These are great, and only use 1.7w since it has a built-in economizer.

TE Connectivity EV200AAANA 500a 0-900vdc Tyco 12/24v

These were recovered from EV battery modules. These are VERY EXPENSIVE online. If you have any project that needs a high current relay this is your chance to save some money. Make a cheap 30a BMS into a 500a BMS. This will work for batteries in the 9-36v range so perfect for Lifepo4 and Lithium...

batteryhookup.com

That one is interesting. Here is something that popped up with a 600vdc search.

https://www.farnell.com/datasheets/2710395.pdf

I am not sure of the cost, I found it here-

https://www.newark.com/c/automation-process-control/motors-motor-controls/contactors-accessories/contactors?operating-voltage=600vdc

This is a darn good thread.

 

[12VoltInstalls]

it is a bimetalic switch.... so technically no because it is for a 30 amp 240 vac appliance. like is that copper wire rated for DC it doesn't care

Derate for DC on a AC device is 5%, occasionally 10%. So 30A 120VAC is 3A 12VDC and the voltage has a derate calc that I can’t recall how to do. Those are “round numbers” not calculated numbers but much above 5A DC I would just get a DC rated product that is sufficient for volts and amps required.
Even DC wire is rated for the conductor amps and volts, with a factor for the sheathing as I recall, and open air vs enclosed(conduit), plus environmental rating (UV, oil, gasoline, water)

 

[Maitake]

OP has been gone for months.
Did they burn the house down?

 

[Ampster]

OP has been gone for months.
Did they burn the house down?

Haha, And the thread goes on without him.

 

[OzSolar]

Haha, And the thread goes on without him.

? There are an impressive number of threads where people go full on "rock em sock em" for months on end but the OP has never once returned to see the dumpster fire they started.

 

[GSXR1000]

Derate for DC on a AC device is 5%, occasionally 10%. So 30A 120VAC is 3A 12VDC and the voltage has a derate calc that I can’t recall how to do. Those are “round numbers” not calculated numbers but much above 5A DC I would just get a DC rated product that is sufficient for volts and amps required.
Even DC wire is rated for the conductor amps and volts, with a factor for the sheathing as I recall, and open air vs enclosed(conduit), plus environmental rating (UV, oil, gasoline, water)

you are also talking 38vdc vs 240vac... so the "longer" dc arc would be smaller due to much much lower voltage... it would work with zero issues

 

[efficientPV]

You won't find those rules printed anywhere because they were just made up. Arcing has to do with the voltage, speed of the opening, distance, current and very important, contact material. Primarily the melting temperature of that material. Copper and silver make very low resistance contacts, but they melt very easily and those vaporized atoms make a good conductor for the arc. Contrary to belief, the plasma arc is not the hottest section. It is the transition from metal to the plasma which is hottest. This is the reason EDM machining works. Tungsten is often used for water heater thermostats because of its high melting temperature. While relays seem fast, they can be quite slow if there is a diode connected across the coil. Big contactors have a lot of distance between contacts and there are generally two in series making the gap extra large. The quick and dirty method is to place several contacts in series. A three phase relay could have six gaps the arc would have to pass. There are no set rules of what can be used safely unless an agency has approved it. In some DC breakers and relays there is a magnet which pulls the arc making the distance longer. This is the reason the contacts have polarity. A good book is Gaseous Conductors by James Dillon Cobine in print for more than 70 years.

 

[Vigo]

Since we're talking quick and dirty already, i had recently wondered.. can you put lower DC voltage rated fuses in series to increase their ability to extinguish an arc?

Because there are many cheap high amp fuses available with ratings of 42vdc for example, that i would happily use on my <58v system, if that approach was 'valid'.

I do have a Class T fuse anyway. Just asking..