Seeking Normally Closed Latching Contactor and Q&A about balancing my Li Ion battery bank

LostinSpace · July 2017

Wondering is anyone is using latching contactors in their system design for High and low voltage cutoff (HVD/LVD). I'm shopping for a 12vdc normally closed, latching contactor. So, the contactor is normally conducting, but if 12v is applied to the terminals it latches open, regardless of if that 12 volts goes away.

You don't seem to find these babies on any street corner.

Please Note: This tread has evolved. LostinSpace has asked that this note be placed here--Lots of evolution of thoughts and ideas during debugging and use of system. -Bill B Moderator

UPDATE: This thread started off as a search for a normally closed contactor that would draw power only to switch state when a trigger even occurred. However, a member (@karrak) after seeing a photo of my array suggested a way the pack could be configured more efficiently. In doing so I uncovered a major problem wherein the cells of the pack were not staying balanced... in spite of thorough attempts to do so. The majority of this thread is the process of discovering why the pack wouldn't balance.

LostinSpace April 4th, 2018

dennis461 · July 2017

How many amps AC or DC, how many contacts?

LostinSpace · July 2017

100 Amps. Single pole single throw should do it. (I'm just interrupting the battery to inverter/cc cable on one side).

mcgivor · July 2017

It would be reletivaly simple to achieve electrically, but it sounds mechanically latching is what you are seeking, correct?

mike_s · July 2017

Linky

LostinSpace · July 2017

mcgivor, yes, mechanically latching. I want the relay to stay open in case of loss of 12v to coil.

mike_s, Mouser, of course. I can't tell from the data sheet if the contacts are normally closed. The unit seems to use two coils. Do you happen to know for a fact that it is mechanically latching? But no worries. I will contact Mouser. Thank you!

mcgivor · July 2017

Have you considered using an external relay to control the contactor such as a ratchet or toggle relay, i've used the one in the pdf extensively in security system, just throwing ideas your way.

mcgivor · July 2017

Link to DC latching contactor
http://www.ametekswitch.com/products/DC-Contactors-List.aspx

LostinSpace · July 2017

Thanks mcgivor. Ideas are good. However, I already have a JLD 404 meter in place, which has a relay that is triggering the current contactor I have. And I will continue to use the 404 with the normally closed latching contactor I hope to find and replace the non latching normally open device I already have.

http://www.evwest.com/catalog/product_info.php?products_id=162

Solray · July 2017

Couldn't you just program logic gates to operate solonoids that open and close switches?

mike_s · July 2017

LostinSpace said:

mcgivor, yes, mechanically latching. I want the relay to stay open in case of loss of 12v to coil.

mike_s, Mouser, of course. I can't tell from the data sheet if the contacts are normally closed. The unit seems to use two coils. Do you happen to know for a fact that it is mechanically latching? But no worries. I will contact Mouser. Thank you!

It's a latching relay. They're bi-stable. Energize one coil, the contacts open and stay open. Energize the other coil, and the contacts close and stay closed. You do want a way to reset it, right?

You don't continuously energize the coils, you pulse them to set/reset.

BB. · July 2017

BlueSea makes a bi-stable battery disconnect. May be over kill for your needs:

https://www.bluesea.com/products/category/20/95/Solenoids/ML-Solenoids

-Bill

LostinSpace · July 2017

Solray, yes, I suppose so, although that's a bit over my head so would be a Plan B. ;>

mike_s, Sweet. That's the baby I want then.

BB., That one looks like it would fit the bill too. Now it's just a question of price as to which one I will try out.

I like this forum. My biggest fear about posing such questions in forums is that someone will respond with the dreaded "What are you trying to do?" You know what I mean? Because if you answer that question the post turns into people critiquing your approach, and you never get your question answered. :<

So thank you.

littleharbor2 · July 2017

Most contributors here are here to help. There are a few who seen to mostly have negative or otherwise valueless replies.

Solray · July 2017

> @LostinSpace said:
> Solray, yes, I suppose so, although that's a bit over my head so would be a Plan B. ;>
>
> mike_s, Sweet. That's the baby I want then.
>
> BB., That one looks like it would fit the bill too. Now it's just a question of price as to which one I will try out.
>
> I like this forum. My biggest fear about posing such questions in forums is that someone will respond with the dreaded "What are you trying to do?" You know what I mean? Because if you answer that question the post turns into people critiquing your approach, and you never get your question answered. :<
>
> So thank you.

You are very welcome. We are always happy to share a point of view or an option you might have overlooked. It's always beneficial to get more sets of eyes on the problem with different perspectives and specialties rather than just an echo chamber where everyone says the same thing.

We do have a few here that always answer everything the same way, your question cannot be answered because I don't know everything about your life history. Lol

bill von novak · July 2017

LostinSpace said:

Wondering is anyone is using latching contactors in their system design for High and low voltage cutoff (HVD/LVD). I'm shopping for a 12vdc normally closed, latching contactor. So, the contactor is normally conducting, but if 12v is applied to the terminals it latches open, regardless of if that 12 volts goes away.

You don't seem to find these babies on any street corner.

Well, if you just want to open when it gets a signal, with a way to manually close it again, then just get a remotely operated circuit breaker. Midnite sells them. 24V to trip, then manual reset. You can probably trip them with 12V although I haven't tried it. (But generating a momentary 24V from 12V is pretty easy with a small relay.

If you really want a latching relay, YM tech makes a line of them. See: http://www.goodymt.com/pdf/LatchRelay.pdf#page=24 for a 150 amp version.

BTW when you are talking about latching relays there's no such thing as "normally closed" - they stay where you put them, so there's no "normally."

LostinSpace · July 2017

bill von novak said:
BTW when you are talking about latching relays there's no such thing as "normally closed" - they stay where you put them, so there's no "normally."
I'll look into that circuit breaker. It may do. That gives me at least 4 options now... just checking out pricing and whatnot now.

I see your point on the normally closed language. None of the spec sheets for latching relays use that language. Hadn't worked with such an animal before.

Solray said:

>You are very welcome. We are always happy to share a point of view or an option you might have overlooked. It's always >beneficial to get more sets of eyes on the problem with different perspectives and specialties rather than just an echo chamber >where everyone says the same thing.

Yes. There's a balance. What I am actually trying to do is obvious I guess (and I suppose typical). This first timer system I just brought up is working, but now that I see how everything operates there is room for fine tuning. The Magnum inverter has a low voltage disconnect, but I wanted a backup given that LPFs are in use (especially after recently reading in the Midnite forum about a guy who had his charge controller bleed his batteries out even though his inverter had turned off, made me even more certain I wanted a fallback disconnect).

The vendor who sold me my batteries specified the LVD contactor. It's fine, but it is non-latching, normally open contacts. The relay uses 3/4 amp and is energized at all times (from a car battery, connected to a charger, plugged into the inverter output). Since I am only powering a freezer at the moment (baby steps) which uses 1.25 amps resting, the relay draw really stands out. The vendor has a more expensive contactor that draws only .15A, but I thought why even spend .15A if there's a better way? So I started wondering about the idea of a latching relay... and sure enough they exist!

So I am thinking I can program the two low current relays on my JDL-404 meter (assuming you guys know what that is) for high and low cutoff, wire the relays in parallel, and if either trips it will supply power to the relay and latch the contacts open (assuming SPST). And having to manually reset the relay is fine by me. :>

Estragon · July 2017

Makes sense to me. The only issue that occurs to me is finding the right LVDC value that does the job but doesn't cause nuisance trips when the freezer current spikes on startup when Vbatt is at the lower end of okay. Is there a delay in the meter triggering its relay (ie a few seconds that Vbatt has to be < TriggerValue for it to close)?

Solray · July 2017

This is where a programmed circuit has an advantage.

LostinSpace · July 2017

Right. I've been through the settings on the 404 meter and it does not seem to allow for a time buffer. However, remember that this circuit is a fail safe. Normally the Magnum inverter will act as low voltage disconnect. I have the Magnum programmed to disconnect at pack voltage 48v (2.7v per cell). I suppose I will set the contactor to turn off at perhaps 40v (2.5v per cell). It's there to keep the pack from completely crashing (values subject to change!)

And so far the LVD on the Magnum has not triggered when the freezer comes in. Naturally this is a subjective comment as I don't know how the magnum will behave with multiple loads PLUS borderline pack voltage. It might be interesting to see if the Magnum has a cutout buffer.

Same on the high side. In this case the charge controller is keeping the lid on pack voltage. It's floating the cells at around 3.3v. Does the cc need a backup? I just came across a thread on the Midnite forums where a guy had a rare failure of a Classic 150 whereby the cc allowed unregulated panel voltage to get to the pack. The battery voltage was raised sky high to the panel voltage and the Calb cells were bulging when he discovered the fault. If a HVD had been set at, what, 3.65-3.7v per cell, perhaps such a disaster would have been avoided.

Raj174 · July 2017

Hi LostinSpace,
As you can see by my signature our systems are very similar. I choose to use a JDL-404 also. I have HVD and LVD contactors on a 12AH battery with tender. I also used a piezoelectric alarm. Been up and running 14 months and have had no high or low shutdown. Glad to see you're using LFP.
I mounted the JDL-404 in the front panel of the inverter. (photo below)
Good luck with your system,

Rick

jonr · July 2017

Microprocessors are now so cheap and low power that I'd use one (plus a latching contactor) for most power switching logic. Make things like brief overload, time of day, intermittent operation, monitoring multiple cells, etc easy.

Estragon · July 2017

So if you've found values that protect the bank on LVDC and HVDC, and don't cause nuisance trips, I'd call that a win!

Raj174 · July 2017

Yep, top balance, charge to 99 percent and stay out of the lower knee in the discharge curve which, for LFP, is below 20 percent SOC. Easy peasy and definitely a win.

karrak · July 2017

LostinSpace said:

Right. I've been through the settings on the 404 meter and it does not seem to allow for a time buffer. However, remember that this circuit is a fail safe. Normally the Magnum inverter will act as low voltage disconnect. I have the Magnum programmed to disconnect at pack voltage 48v (2.7v per cell). I suppose I will set the contactor to turn off at perhaps 40v (2.5v per cell). It's there to keep the pack from completely crashing (values subject to change!)

And so far the LVD on the Magnum has not triggered when the freezer comes in. Naturally this is a subjective comment as I don't know how the magnum will behave with multiple loads PLUS borderline pack voltage. It might be interesting to see if the Magnum has a cutout buffer.

Same on the high side. In this case the charge controller is keeping the lid on pack voltage. It's floating the cells at around 3.3v. Does the cc need a backup? I just came across a thread on the Midnite forums where a guy had a rare failure of a Classic 150 whereby the cc allowed unregulated panel voltage to get to the pack. The battery voltage was raised sky high to the panel voltage and the Calb cells were bulging when he discovered the fault. If a HVD had been set at, what, 3.65-3.7v per cell, perhaps such a disaster would have been avoided.

Another option instead of the relay is a Solid State Switch like this http://www.ebay.com.au/itm/Solid-State-Relay-SSR-1-DD60D200-200A-5-60VDC-3-32VDC-/111670587666. These should use very little power when powered on or off.

If your inverter had a remote on/off switch input you could use that instead of the relay. I had a look at the manual and couldn't find anything. It would be slightly more complex but you could hook a small relay across the on/off switch on the front of the inverter and pulse it to simulate pressing the on/off switch. To make sure that it had indeed turned off you should probably monitor the current to see if it drops to nearly zero to make sure that the inverter has turned off.

On my LFP battery I haven't bothered having a relay to disconnect the inverter. My reasoning is that I will have to be around using the power to drain the battery so will hear an audible alarm. If I am away from home and if my solar controller fails, all the equipment left running will take around a week to flatten the battery and I can monitor the battery SOC remotely via the Internet on my phone.

For the charge controller cutoff, you are better off disconnecting the solar panels from the controller rather than the controller from the battery. You could use a smaller Solid State Relay to do this. In the classic manual they mention that there is an internal relay to disconnect the panels at night. If this is the case I would think that if the classic detected a fault that it could disconnect the panels via the internal relay. Would be good if Midnite made it possible to switch this relay off remotely. Might be worth a phone call to them to discuss this.

I agree with Raj, that it is a good idea to have some sort of audible alarm as well.

Your signature mentions a BMS, do you have any details on what BMS your battery has connected to it?

Simon

jonr · July 2017

> you could hook a small relay across the on/off switch on the front of the inverter

I agree - I did this and it worked well (arduino controlling the inverter).

Nice price on the DD60D200 200A DC SSR (if it holds up under use).

BB. · July 2017

Watch out for the solid state relays--There are a lot of counterfeit product out there. If the price is "too good to be true"--It may be.

http://canada.ul.com/safetyalerts/ul-warns-of-solid-state-relay-with-counterfeit-ul-recognition-mark-release-13pn-52/
http://www.instructables.com/id/The-inner-workings-of-Counterfeit-FOTEK-SSRs/

Also, (it appears) that many of the counterfeit SSRs failed shorted (on). Not a good thing for your application.

-Bill

PS: I should also add that SSRs (in general) need to be well heat sinked. They run much hotter than a typical mechanical relay.

bill von novak · July 2017

BB. said:

Watch out for the solid state relays--There are a lot of counterfeit product out there.

I would also add that even "real" SSR's often have poor specs. For example, a lot of AC SSR relays have 2 volt drops across them. At 40 amps that's 80 watts that has to be dissipated in a heatsink. DC SSR's are _usually_ better but not always - and even .01 ohm at 100 amps results in 100 watts of dissipation.

BB. · July 2017

I agree Bill... SSRs are not wonderful for applications where mechanical relays are OK for the application (typically an average sized mechanical really uses something like ~6 Watts for the coil). And you can usually get then in NC or NO (or both) configurations (i.e., power on for closed/on connection or power on to open/turn off).

-Bill

LostinSpace · July 2017

karrak said:
For the charge controller cutoff, you are better off disconnecting the solar panels from the controller rather than the controller from the battery. You could use a smaller Solid State Relay to do this. In the classic manual they mention that there is an internal relay to disconnect the panels at night. If this is the case I would think that if the classic detected a fault that it could disconnect the panels via the internal relay. Would be good if Midnite made it possible to switch this relay off remotely. Might be worth a phone call to them to discuss this.

I agree with Raj, that it is a good idea to have some sort of audible alarm as well.

Your signature mentions a BMS, do you have any details on what BMS your battery has connected to it?

Simon

Thanks for this input Karrak. Ideally I would like to employ one mechanism to disconnect the batteries, so a cutoff that literally breaks the cable connection from the batteries seems the simplest and most assured approach. Unless you know of some compelling reason to not have solar juice entering the cc if it is powered off??

On the audible, I've ordered a celllog 8, which has one built in.

On the BMS, I would be happy to message you privately with what I'm using, but I'm concerned that mentioning anything to do with battery management here will take the thread off topic. :>

LostinSpace · July 2017

Raj174 said:

Hi LostinSpace,
As you can see by my signature our systems are very similar. I choose to use a JDL-404 also. I have HVD and LVD contactors on a 12AH battery with tender. I also used a piezoelectric alarm. Been up and running 14 months and have had no high or low shutdown. Glad to see you're using LFP.
I mounted the JDL-404 in the front panel of the inverter. (photo below)
Good luck with your system,

Rick

Hey Rick. I see you cut metal to mount that meter. You are braver than me. How did you make such a nice cut?

Let me ask you, is that HVD/LVD contactor a normally open device, using 12v juice to keep the contacts closed?

Seeking Normally Closed Latching Contactor and Q&A about balancing my Li Ion battery bank

LostinSpace April 4th, 2018

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