Simple LiFePO4 system, soliciting comments

[Hkalan]

Hello,

If you incorporate a CellLog 8s into your system ($15 USD), and have a relay on the Alarm port for your HVC as a backup disconnect. Not to expensive !

I am using the CellLog 8s as the backup LVC Alarm that is wired directly into the inverter. As I also have the Victron Blue Power Panel VE.Net full system monitoring. I am able to connect that to a relay as another HVC back up cutoff.

All comes down to how well you want to protect your system.

Alan

[durundal]

Originally Posted by Hkalan

Hello,

If you incorporate a CellLog 8s into your system ($15 USD), and have a relay on the Alarm port for your HVC as a backup disconnect. Not to expensive !

I am using the CellLog 8s as the backup LVC Alarm that is wired directly into the inverter. As I also have the Victron Blue Power Panel VE.Net full system monitoring. I am able to connect that to a relay as another HVC back up cutoff.

All comes down to how well you want to protect your system.

Alan

My concern with the cell log is that you have to get a DC/DC converter for it or else it will bring whatever cell is driving it out of balance with the rest. For the price maybe it's worth just getting a little converter and replacing it semi annually but it would really be nice to be able to buy the equivalent of that that runs off 12V and is marinized for $50. In my case it's a 22' trailerable boat so I'm expecting that any electronics that aren't sealed will get wet and break sooner or later (and shake themselves on the trailer).

[Hkalan]

Hello,

My house bank is 24v, so I installed a cigarette lighter receptacle from the generator 12v bank. Located it about a meter from the CellLog 8s, and use a simple mobile phone car charger adapter that has 2 USB ports from the cigarette lighter side. Plug in the USB cable, and there is now balance in the universe !

Alan

[marujo.sortudo]

Originally Posted by durundal

This is my concern with the BMS units I've seen so far, they all appear to be un-ruggedized PCBs (maybe not even conformal coated?) that are diving board attached to one of the cell lugs. Even if they work as designed that's a fatigue failure waiting to happen, is there any sort of plug and play ruggedized unit with cell level monitoring similar to the house power setup? Any equipment capable of performing shunting functions is just another possible failure mode for small systems like this, just a bank shut off if something goes wonky is sufficient (in my case in a little coastal cruiser take it home and debug there). I also am setting up a 12V 100Ah system and am ok with the risk of the cells longevity being compromised but not with something falling off and possibly shorting across terminals causing a fire. It would be great to monitor cell voltages to catch a potential problem but not at the expense of reducing total system reliability.

I have your same concerns, but decided to go with a MiniBMS system mainly to provide HVC in the event of an alternator regulator failure. The wiring with cell boards on a 100Ah bank gets wicked crowded and I plan on boxing up the whole bit to try to keep it dry should a wave ever make it below decks near the bank. There does seem to be some slight coating on the board, but it doesn't remind me of marinized electronics. I noticed after the fact that they have a MiniBMS 4S cell board that would allow you to put all the cellboards and the BMS unit together in an enclosure which could help.

Originally Posted by durundal

I am only charging from a Genasun lithium MPPT controller which I think is reasonably likely to fail safe, but am considering one of those latching relays (thanks for the link, I had been hunting for something like that for a while!) to turn off the panel if it tries to overcharge somehow (two required failures to produce an overvoltage condition, genasun has to not limit voltage and the Prolatch has to not work). If the bank dies due to low voltage that's at least an energy-poor condition so less likely to set my boat on fire though it could kill cells, maybe worth a second Prolatch to avoid that case anyway.

Alas, those relays have a very configurable LVC, but the HVC is not configurable at all and is up near 15V. This is too much for LiFePO4 which is why I've elected to use a BMS for my HVC, albeit somewhat reluctantly. I did also consider driving my charge sources through NC relays hooked up to the alarm connection on my battery monitor. This would be somewhat stupid in that it would cut charging on HVC, LVC or any other alarm condition, so a manual override would be needed to recover from an LVC event. I haven't researched if the battery monitor is configurable enough for this purpose, and obviously this wouldn't involve any cell level monitoring, so investigate this fully if you intend to go this route.

There seems to be a little weirdness with the Sterling ProLatch, too, where when it powers up if first disengages for 1-2 secs and then reengages. This isn't a big deal for me as I generally leave the battery switch on.

[durundal]

Found these interesting looking voltage monitoring relays:

Voltage Monitoring Relays for Protection Against Voltage Faults

I believe they can be configured to have the solenoid sit unenergized up until the high voltage band is breached, at which point it would energize and (for my purposes, limited to 5A) disconnect the solar panel until the battery voltage drops. Spec sheet says 3W power draw but I assume that must be for the energized state.

On the downside, can't seem to find any units actually in stock from the usual electronics suppliers I know...

(and to save some time if you, like me, were unfamiliar with the terms they use in their spec sheets:

Pick up voltage (also defined as pull in voltage, or must operate voltage): As the voltage of a de-energized relay is increased, the value at or below which all contacts must function.
Drop out voltage (also defined as release, or must release voltage): As the voltage on an energized relay is decreased, the value at or above which all contacts must return to their de-energized position.)

[Wireless1]

These relays look to me like they are for monitoring 3 phase AC voltages for AC motor circuits, and trip if any of the phase voltages get out of the preset range. Don't think these are anything to do with DC.

[durundal]

There are many flavors, DC and AC. Look at the part number option lists closer.


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[Wireless1]

Originally Posted by durundal

There are many flavors, DC and AC. Look at the part number option lists closer.

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Thanks for pointing that out. Boy...they sure don't make it easy on someone looking for DC models. You'd think they would mention something as simple as AC AND DC voltage/current sensing models available in the product photo blurb, but instead they make is sound like it's all AC phase sensing. Good on you for searching further. Had to download what was called the catalog, and then fish around for it. Then again, at my age I don't see a LOT of obvious things! Ha!

After reading the relay parameters I don't think they will work for me as the drop out on their 48 volt relay is 53 volts? A wee low at 3.4 volts per cell when my Voltronix (2p,16s) LiFePO's are 3.6 nominal. See, I'm kind of stuck between what the EV guys are doing, and what the boat house battery guys are doing. I am using EV technology to drive the boat, but am stuck using low C charging rates with solar and wind like the house battery guys use. In an electric propulsion boat I'm thinking I really don't want LVC cutout. LVC alarm yes, cut out, no.

[goboatingnow]

In my opinion battery level HVC , LVC, monitoring is a waste of time. In reality you are adding s that you take this 5-day course of instruction. BST is actually 4 courses – Basic Firefighting, Personal Survival, Personal Safety and Social Responsibility, and Elementary First Aid. This course has to be renvery little protection as an individual cell could fall to very low voltages or attain high voltages and neither system would detect it. In particular cell low voltage is very dangerous

If you are going to bother them do it right in my opinion.

Dave

[DeepFrz]

In reality you are adding s that you take this 5-day course of instruction. BST is actually 4 courses – Basic Firefighting, Personal Survival, Personal Safety and Social Responsibility, and Elementary First Aid.

GBT, what are you talking about?

[Wireless1]

Originally Posted by Wireless1

After reading the relay parameters I don't think they will work for me as the drop out on their 48 volt relay is 53 volts? A wee low at 3.4 volts per cell when my Voltronix (2p,16s) LiFePO's are 3.6 nominal. See, I'm kind of stuck between what the EV guys are doing, and what the boat house battery guys are doing. I am using EV technology to drive the boat, but am stuck using low C charging rates with solar and wind like the house battery guys use. In an electric propulsion boat I'm thinking I really don't want LVC cutout. LVC alarm yes, cut out, no.

Doh!... Correcting my own mistake here, and not the first time I've quoted my LiFePO4's as having the wrong nominal voltage. They are 3.2 NOT 3.6... My bad.

[goboatingnow]

Originally Posted by DeepFrz

GBT, what are you talking about?

Huh why are u cross quoting

Dave


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[colemj]

Dave, he is right - look at your post and see if it makes sense to you. I can't make heads or tails of it.

Mark

[durundal]

It's an inadvertent cut and paste error, should read:

In my opinion battery level HVC , LVC, monitoring is a waste of time. In reality you are adding very little protection as an individual cell could fall to very low voltages or attain high voltages and neither system would detect it. In particular cell low voltage is very dangerous


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[goboatingnow]

Originally Posted by colemj

Dave, he is right - look at your post and see if it makes sense to you. I can't make heads or tails of it.

Mark

Oh I see, must have been a cut and paste screwup on my behalf.

I was saying that monitoring HVC and LVC are only useful. At cell level. Battery level monitoring is far less useful and in fact can result in cell extremes not being detected. If you are going to the cost of installing good quality high ampere disconnects , it makes no sense to then leave out the cell monitoring

Dave


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