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CatNewBee · 09-08-2019, 05:53

Your voltage drop is a function of the current fowing through the wires, in your example it was 0.08V, you can measure it also indirectly by comparinf the voltages at charger terminals vs. Battery terminals.

Regarding balancing, it depends. If you usefix preset balancer modules, the cells will not be balanced, if you have an adjustable bms, you can configure the set points to meet your needs.

Balancers kick in ar a preset voltage at cell level,if the cells are way out of balance, even at 13.8V pack voltage a single cell can be above 3.65V.

Usually you want the setup
That way, that balancing takes place only when a charging current is flowing, so well above the resting voltage of the cells, but also that low, that at least three, better all four balancer are active before you stop charging, so the cells get as equal as possible, but not over charged.

Balancing current is usually quite low 1...3A, way lower than the charge current, no problem when burning a small part of the charger energy for balancing.

JetPack · 12-08-2019, 01:47

Please define large bank. Is 4 in parallel large? There are lots of YouTube video showing the LiFePo4 being abused including overcharging. No fire. So. You are saying a few cells charging a defective one will cause fire? Do you have any references for this? Thanks

CatNewBee · 12-08-2019, 05:42

Quote:

Originally Posted by JetPack

Please define large bank. Is 4 in parallel large? There are lots of YouTube video showing the LiFePo4 being abused including overcharging. No fire. So. You are saying a few cells charging a defective one will cause fire? Do you have any references for this? Thanks

I am not saying fire, but maybe bulging and blowing the over-pressure protection vent and causung a lot of unhealthy smoke.

The larger the capacity, the more energy is there, more energy, more trouble. But even a small smartphone battery can produce significant heat as you know, this are LiPo, and may catch fire in contrast to LFP, but as I said, more energy, more pottential damage.

Cpt Pat · 12-08-2019, 11:05

Quote:

Originally Posted by CatNewBee

I am not saying fire, but maybe bulging and blowing the over-pressure protection vent and causung a lot of unhealthy smoke.

The larger the capacity, the more energy is there, more energy, more trouble. But even a small smartphone battery can produce significant heat as you know, this are LiPo, and may catch fire in contrast to LFP, but as I said, more energy, more pottential damage.

Did your battery come with a materials safety data sheet? To my knowledge, most don't. Here's what I found: https://www.klinger.fi/wp-content/up...iFePO4-SDS.pdf

"If the electrolyte contacts with water, it will generate detrimental hydrogen fluoride." Water, like in your eyes and respiratory track.

So, you may not get a fire... only toxic gasses that choke and blind you. If the battery starts outgassing: GET OUT! And hope there isn't a thermal fire from whatever may have short circuited the battery - which you can't get close enough to fight.

**newhaul** · 12-08-2019, 11:21

Quote:

Originally Posted by Cpt Pat

Did your battery come with a materials safety data sheet? To my knowledge, most don't. Here's what I found: https://www.klinger.fi/wp-content/up...iFePO4-SDS.pdf

"If the electrolyte contacts with water, it will generate detrimental hydrogen fluoride." Water, like in your eyes and respiratory track.

So, you may not get a fire... only toxic gasses that choke and blind you. If the battery starts outgassing: GET OUT! And hope there isn't a thermal fire from whatever may have short circuited the battery - which you can't get close enough to fight.

I bet for the electrolyte to come into direct contact with seawater on a boat in sure the offgassing is the least of our worries at that point.

andyalford · 13-08-2019, 06:12

I am trying to design my LVD / HVD contactor circuit for the new version of REC-ABMS for Victron CCGX - the Active BMS that communicates with CAN-bus to a Victron GX Device to control voltage and current during charge and discharge.

The BMS checks the individual cell voltages / temperatures, and send maximum charge voltage & current to the GX Device which broadcasts this to all AC Chargers & Solar MPPT controllers in the network. But, of course, it ignores alternators and makes no allowance for DC Loads.

Is there anyone else who has gone through this process already? I am struggling with some details in the manual and would love to compare notes with someone with recent experience.

Big thanks to @CatNewBee who has been superbly helpful with providing his own experiences for us, but his REC-ABMS is the previous version, so he has solved this particular puzzle somewhat differently.

I am considering putting together a Wiki for this, to publish my results for other to read and update. But first things first ... I need to make it work!!

P.S. I am actually going to be doing this with a Raspberry Pi version of Venus OS, rather than a CCGX. So I will be getting access to more internal information from the CAN-bus and other components. Should be interesting.

john61ct · 13-08-2019, 10:00

I think such a commendable project is worth starting a new thread for.

Then when/if you do decide to host a wiki, everything will be documented in one place without other diluting / diverting discussions mixed in.

Of course point to it from here so those reading this thread in coming years can easily benefit.

SweareDeep · 13-08-2019, 11:09

[Long time reader, first time poster]

With an alternator regulator such as the Wakespeed 500 then the alternator could be included in the CANbus control from the REC-BMS. Also, REC make a Bistable Latching Relay Controller so you could avoid some of the extra circuitry that CatNewBee had to add in order to use Blue Sea latching relays.

I've been going through a similar thought process for an anticipated upgrade to LFP batteries. However, I'm now leaning towards limiting the BMS to battery protection and monitoring to maximize reliability, possibly using a Lithionics system. I want to minimize the risk of problems offshore. Then, on top of that, if I wish to do something other than the programmed charge profile in the various charging devices (alternator, solar, hydro, shore), such as floating early to achieve 50% SOC, then I will do that manually or through a Venus OS device talking CANbus.

One area I'm still thinking about is unattended mode. Suppose we're leaving the boat for a couple of weeks some place to fly home, what's the best thing to do? I'm thinking it may be to switch off the LFP system completely (at say 50% SOC) and run the boat off shore power into the starting battery (AGM) to keep things ticking over in our absence. In my experience, unfortunate things like the shore power being unplugged sometimes happen in marinas, and I wouldn't want to put my LFP battery in harm's way.

Cpt Pat · 13-08-2019, 15:09

Quote:

Originally Posted by yachtshah

I am trying to design my LVD / HVD contactor circuit for the new version of REC-ABMS for Victron CCGX - the Active BMS that communicates with CAN-bus to a Victron GX Device to control voltage and current during charge and discharge.

The BMS checks the individual cell voltages / temperatures, and send maximum charge voltage & current to the GX Device which broadcasts this to all AC Chargers & Solar MPPT controllers in the network. But, of course, it ignores alternators and makes no allowance for DC Loads.

Is there anyone else who has gone through this process already? I am struggling with some details in the manual and would love to compare notes with someone with recent experience.

Big thanks to @CatNewBee who has been superbly helpful with providing his own experiences for us, but his REC-ABMS is the previous version, so he has solved this particular puzzle somewhat differently.

I am considering putting together a Wiki for this, to publish my results for other to read and update. But first things first ... I need to make it work!!

P.S. I am actually going to be doing this with a Raspberry Pi version of Venus OS, rather than a CCGX. So I will be getting access to more internal information from the CAN-bus and other components. Should be interesting.

I'm using this for low voltage cutoff, set to 12.7 volts, no delay (with normal loads, the voltage on the bus is actually 12.8 volts, with a 0.1 volt resistive drop): APO3: Automatic Power Off 3 - APRS World, LLC

I set the Victron relay to open at 80% SoC (nominally) and to close at 79% SoC for charge resumption. If you use the Victon to control your charge cutoff using the SoC counter, then you can't configure the relay for any other setting - all other relay thresholds will override the SoC configuration. You can set the alarms anywhere you want (but the alarm isn't very loud).

I avoid using any type of computer for BMS controls - I want deterministic "appliances" controlling the parameters. But since I work in computer risk management - I'm a bit paranoid...

CatNewBee · 14-08-2019, 02:32

Our boat was at the marina for last winter, I just changed the settings on the solar controller. All batteries remain online to the charge bus, BMS was watching the battery, SOC was around 80%, AIS, bilge pumps on, everything else off. Not too bad. After the winter settings back to normal.

andyalford · 14-08-2019, 08:34

Quote:

Originally Posted by SweareDeep

[Long time reader, first time poster]

With an alternator regulator such as the Wakespeed 500 then the alternator could be included in the CANbus control from the REC-BMS. Also, REC make a Bistable Latching Relay Controller so you could avoid some of the extra circuitry that CatNewBee had to add in order to use Blue Sea latching relays.

Thanks for introducing this option to me. But now I have seen the complexity and cost, I realise that it is not that important to me! I am currently planning on a HVD energised relay to the 12V supply of my existing Balmar MC614 regulator. LFP doesn't seem to need a fancy profile from what I have read so far - "maximum current from the alternator & belt limited by the Alternator temperature" I think this will involve a bit of experimentation. Before I buy another Balmar unit (for my second alternator) I expect to search for an OpenSource Alternator controller, as it just doesn't seem that difficult. But pride comes before....

Quote:

Originally Posted by SweareDeep

I've been going through a similar thought process for an anticipated upgrade to LFP batteries. However, I'm now leaning towards limiting the BMS to battery protection and monitoring to maximize reliability, possibly using a Lithionics system. I want to minimize the risk of problems offshore. Then, on top of that, if I wish to do something other than the programmed charge profile in the various charging devices (alternator, solar, hydro, shore), such as floating early to achieve 50% SOC, then I will do that manually or through a Venus OS device talking CANbus.

I have been so impressed with the VENUS OS for RPi. The support from that community seems to be amazing. I am looking forward to getting that going. Then Tank sensing with Arduino, OpenPlotter, OpenCPN for RPi, etc...

I looked at Lithionics, but couldn't get enough hits for people using that combination of equipment. Of course, there are a fair few folks using REC BMS for DIY battery packs, and all seem to have things working. I'm not brave enough to do the OpenBMS thing just yet!

Quote:

Originally Posted by SweareDeep

One area I'm still thinking about is unattended mode. Suppose we're leaving the boat for a couple of weeks some place to fly home, what's the best thing to do? I'm thinking it may be to switch off the LFP system completely (at say 50% SOC) and run the boat off shore power into the starting battery (AGM) to keep things ticking over in our absence. In my experience, unfortunate things like the shore power being unplugged sometimes happen in marinas, and I wouldn't want to put my LFP battery in harm's way.

Interesting what @CatNewBee says about his well established installation. I will have this same challenge, though no shore power to worry about, as the boat will be on a mooring or at anchor when I leave her. But I would like to think that VRM will allow remote access and some comfort to see all is going well, and I think that it should be possible to change parameters if you notice something wrong. Certainly, I think that is the intention of VRM to allow remote configuration of non-managed power installations (e.g. on snow covered mountains, etc.)

Yes... I was never so worried about those old Trojan T105's....

andyalford · 14-08-2019, 23:17

By the way, anyone interested in Blue Sea Systems ML-RBS 7700 contactors. They are on some kind of crazy discount at amazon.com right now $136-142. This is less than trade price is $152 ! They were $190 last week.

Blue Sea Systems 7700 ML-Series Remote Battery Switch with Manual Control (12v DC)

**newhaul** · 15-08-2019, 07:37

I just got an email from renogy . They are now doing preorder for a 50 amp b2b charger with a combined solar mppt controller .
https://www.renogy.com/products.php?...eid=4d9301f21b

And at $300 it sounds like a good deal .