Source for Solid State - Normally Closed Relay?

[Marinepower]

I have 2 applications where a normally closed relay is needed.  

One is a shunt trip on a Midnite solar breaker and the other is a shore charger with a remote switch which oddly requires 12v positive to stop charging.  I guess I could also put a NO AC relay on the shore power's AC input ( but it draws about 7 amps).

I know that NC relays are not ideal because they don't fail open.

I have been having a difficult time finding any well priced, moderately powered NC -SSR relays.   There is this 3amp DC one from Digikey I found for $40 cad.  https://www.digikey.ca/en/products/detail/sensata-crydom/DC60S3-B/1135091

Anyone find a reasonably priced, 12volt, quality Normally Closed solid state relay?  Solid State is preferred to keep down the power loss.

MP

[Urs]

Hi,

You write your AC-relay draws 7 Amps. Not shure what main voltage you have but at 110V that would eqals to 770W and at 230V to over 1.5kW! Not shure where you got these numbers from, but that can't be. The typical mains relay I know about have a self consumption of around 1 to 2W at 230V. If you search around you may find some consuming even less than that.

As for the SSR I can't give you an advice on which one to take, but the one you linked needs 3-10V to switch on. With 12V (or with lifepo more realistic 13.6-14.2V) I'd expect that one to be damaged if directly connected to 12V.

[Dacian Todea]

MP,

I have still a few breakers with shunt trips and some that need to arrive and I will then provide info on how to drive them.  I will make a post on this forum after I test them.  One of them is a Midnite 125A 125Vdc breaker so maybe the same as what you have. Curious how it will compare with the more robust China made versions at similar price.

To drive all this I plan to use the CPC1705 an NC SSR as the idea is to use with type 5 on the SBMS thus as long as all is OK with the battery and SBMS then EXT IOx will be close circuit (normal open TLP172GM on the new SBMS0)  so this will supply current to CPC1705 input (around 5 to 10mA) trough an apropiatly sized resistor and that means the CPC1705 output will be open circuit when all is normal and so you can enable (turn ON) the breaker but if anything happen so that EXT IOx becomes open circuit (this can include a fault like under or over voltage lock) or can be that SBMS0 lost power or one of the EXT IOx wires is broken (open circuit) the CPC1705 will default to that normal close and energize the breaker trip shunt coil that will trip the breaker.

On the shore power you only need a normal open SSR and should not draw more than 10 to 15mA typical so can be handled by the EXT IOx directly.

 

[Marinepower]

Urs,

I am in Canada so our mains is 120v.  7.5 amps , 120v draw is what the charger manual says.  Find specifications on page 5 in this link to the manual:  http://assets.bluesea.com/files/resources/instructions/980025140.pdf

The input voltage of the NC - SSR I linked to seems to be 3.5v to 32v.  So that should be fine for most applications. See: https://www.sensata.com/sites/default/files/a/sensata-dc60%20series-panel%20mount%20relay-datasheet.pdf

[Marinepower]

Dacian,

yes I ordered the same 125amp Midnite solar breaker as well.  I too am still waiting for it to arrive in the mail.  It seems like a good unit and and is well certified.  

I also intend to use it as type 5 but I have decided to only connect it to the charge bus.  My biggest concern on a boat with LFP is off-gassing and or fire due to a charge source failing to stop charging , so having a second level (type 5) of protection for charging seems prudent.

Thank you for the referral to the CPC1705.  That seems like a good solid state, normally closed relay and I can easily mount it on a project board. 

My system is 12volts and the Midnite solar shunt trip is 24volts.  I could not find a 12volt shunt trip here or with the Chinese sellers.   So I plan to use a  cheap 10amp, 12v/24v boost converter to step up the voltage to the shunt trip. This will double the current draw through the CPC1705.   I assume that these style of shunt trips do not need more than 1 amp at 24 volts to trip?   Probably more like milliamps - but I could not find a specification for the current draw.

As for my shore charger - its remote input needs a high signal to stop charging.  So a normal NO relay will not work for me unless its on the AC feed line of the charger.  See page 10 of the manual linked above:   "the external shutdown input is a ¼" male quick connect. Applying a voltage between +5 and +32 volts DC (referenced to the battery negative) will place the charger into standby mode. When the voltage is removed, the charger will resume charging"

MP

[Dacian Todea]

MP,

Yes most shunt trips are on 24V or 48V as that is standard in low voltage DC automation and it will be harder to find 12V shunt trip unless the manufacturer can custom made one for you (not the case with Midnite).

You should have the 24V side of the DC-DC trough the CPC1705

I will test the exact current needed to trip on all shunt trips I have together with minimum trip voltages and other details so likely this will be a full day of testing for me.

That sort of remote is not safe so I do not understand why company implement that but a NC SSR will work as you connect that between the battery+ and remote input thus charger will be OFF unless the EXT IOx supply current to the CPC1705 input to make the output open circuit and start the charging. So CPC1705 will just work as a logic inverter.

[Marinepower]

My Midnite solar 125A  breaker arrived.  I tested it with a power supply attached to the  12v - 24v boost converter i plan to use.  It seemed to take about 1.6 amps at 12.5v to trip the breaker when in line with the boost converter ( so approx 0.8 amps at 24 volts) .   

Ideally I would like to put the 12-24 boost converter between the CPC 1705 NC relay and the breaker, to avoid the parasitic load of the 12-24v boost converter.  I'm not sure if these boost converters have much capacitance causing an in-rush current.  The  CPC 1705 NC should just be able to provide enough power to trip the shunt, but I imagine that it would not be able to deal with any in-rush currents. Not sure how to measure this?

[Dacian Todea]

MP,

I also got the Midnite 125A but I'm waiting for some other parts before testing and giving my opinion.

The big downside I noticed is that the trip shunt coil is no internally disconnected so if say you get the supply from the Load side of the breaker but for some reason there is still voltage there the coil will be damaged as it is not designed for continues use.

All other trip shunt breakers I have will be disconnected internally once the breaker is tripped thus there is no risk of damaging the coil.

Yes you will most likely damage the CPC1705 if you try to switch ON a captive load like the DC-DC.

I will let you know exactly how much current the Midnite uses as I will have a current shunt connected to oscilloscope (the only way to properly see the current). I will do that for all breakers.

Midnite looked like a great option except for that trip coil.  Please do not test continues like for example at 12.5V 1.6A you have 20W so even in a few seconds the coil can be damaged (to much heat to dissipate for a very small coil).  At 24V it will not be half it will be double the current.

I will do a proper review for all models that I have then make some recommendations. 

[Marinepower]

Oh, that is not great news on the design of the Midnite solar shunt trip.  As you say -  it should work fine for a LVC it you know one side will not be powered after the breaker is tripped.

Thanks for the warning on the potential of shunt trip coil burn-out.  When I did my shunt trip coil amp draw test, I just momentarily touched the wire to the shunt trip terminal, so no issues of coil burn out.

MP

[Tim Rotunda]

I've not read all this thread but in case no one commented on the need for +12v to stop the charge, you could use an NP relay and pull it to ground when you need to power on the device.  Sounds like you would need a pull-up resistor to keep it off until you close the relay to power it on.  In that case, you could use a Optical DC SSR to control the DC load with a tiny dc current to activate the SSR.  By tiny I mean 5ma to activate the load side, which you could run up to 45amps of DC on the load of the SSR's I am thinking of.