Cheap LiFePO4 BMS?

[MtB]

18 minutes ago, MoominPapa said:

Out of interest, how many people here would be interested in a module to control the BDS-A bistable relay from a single input? Total guess at costs might be £25 or £30 if I made a dozen or so.  No promises.

 

MP.

 

 

I think I'd be interested! 

 

To clarify, the bistable relay needs a 150ms pulse to change states. Your module would monitor the output switch terminals of the "8 cell battery monitor module V2" and deliver that pulse each time the state of the output switch on the "8 cell battery monitor module V2" changes?

 

Two modules per lithium battery installation would be needed I think, one to connect to the over-voltage switch terminals and one for the under-voltage switch terminals on the "8 cell battery monitor module V2", if I am understanding correctly. 

 

 

 

 

 

Edited October 24, 2019 by Mike the Boilerman
Clarify.

[MoominPapa]

6 minutes ago, Mike the Boilerman said:

 

I think I'd be interested! 

 

To clarify, the bistable relay needs a 150ms pulse to change states. Your module would monitor the output switch terminals of the "8 cell battery monitor module V2" and deliver that pulse each time the state of the output switch on the "8 cell battery monitor module V2" changes?

Yes.

6 minutes ago, Mike the Boilerman said:

 

Two modules per lithium battery installation would be needed I think, one to connect to the over-voltage switch terminals and one for the under-voltage switch terminals on the "8 cell battery monitor module V2", if I am understanding correctly. 

 

Making the module with two inputs, so it opens the contactor if the "low voltage" input OR the "high voltage" input is active would be trivial.

 

Out of interest, are these outputs volt-free contacts?

 

 

MP.

 

[MtB]

23 minutes ago, MoominPapa said:

Making the module with two inputs, so it opens the contactor if the "low voltage" input OR the "high voltage" input is active would be trivial.

 

That would do the trick nicely!

 

23 minutes ago, MoominPapa said:

Out of interest, are these outputs volt-free contacts?

 

 

From my casual reading of the data sheets, yes. 

 

 

23 minutes ago, MoominPapa said:

so it opens the contactor

 

Presumably sends a pulse to open the contactor?

 

And sends another pulse to close the contactor when the output switch de-activates? 

 

 

P.S. Put me down for two, I'll put some lithiums in Reg too.

 

In fact perhaps Reg could be a test bed for the 'lithiums on a budget' project you were thinking about... (was that you?)

 

 

 

 

Edited October 24, 2019 by Mike the Boilerman

[Dr Bob]

2 hours ago, MoominPapa said:

 

Out of interest, are these outputs volt-free contacts?

 

 

 

 

Yes.

2 hours ago, Mike the Boilerman said:

 

In fact perhaps Reg could be a test bed for the 'lithiums on a budget' project you were thinking about... (was that you?)

 

 

 

 

I think that was Tom

[MtB]

On 20/10/2019 at 01:51, Tom and Bex said:

If I was to install another system, I'd probably use this together with a couple of bi-stable relays 

 

The 'this', for the benefit of peeps who didn't click the link, is this cell monitor for between four and sixteen cells, costing 128 Euros. Appears capable of being configured to give a pulse output for operating bistable, or latching, relays.

https://www.ev-power.eu/Battery-Management/GWL-Cell-Performance-Monitor.html#tab3

 

 

 

On 20/10/2019 at 01:51, Tom and Bex said:

a couple of bi-stable relays such as thiis (often available cheaper 2nd hand on Ebay - try searching for bds-a, Ford battery disconnect, v23130, or 6C1T10B728).

 

Unfortunately the above link appears to be a link to ordinary non-latching relay. The bistable version looks identical visually. I think the correct link is as follows:

https://uk.rs-online.com/web/p/latching-relays/6900802/

 

 

But there is more. I see ev-power.eu have a latching 120A relay for only 11 Euros. Here:

https://www.ev-power.eu/Battery-Management/DC-Power-Latching-Relay-100A-Coil-12V.html?cur=1

So I have just ordered the GWL cell performance monitor board above and three of these latching relays. Total cost including shipping and the 4% PayPal surcharge came almost exactly £200 all in.

 

 

 

 

 

Edited October 24, 2019 by Mike the Boilerman

[Dr Bob]

44 minutes ago, Mike the Boilerman said:

 

The 'this', for the benefit of peeps who didn't click the link, is this cell monitor for between four and sixteen cells, costing 128 Euros. Appears capable of being configured to give a pulse output for operating bistable, or latching, relays.

 

https://www.ev-power.eu/Battery-Management/GWL-Cell-Performance-Monitor.html#tab3

 

Unfortunately the above link appears to be a link to ordinary non-latching relay. The bistable version looks identical visually. I think the correct link is as follows:

https://uk.rs-online.com/web/p/latching-relays/6900802/

 

But there is more. I see ev-power.eu have a latching 120A relay for only 11 Euros. Here:

https://www.ev-power.eu/Battery-Management/DC-Power-Latching-Relay-100A-Coil-12V.html?cur=1

 

So I have just ordered the GWL cell performance monitor board above and three of these latching relays. Total cost including shipping and the 4% PayPal surcharge came almost exactly £200 all in.

 

 

The drawback of your choice of the cell monitor (that will work with the latching relay) and the latching relays, is that you will still have a problem if you try and use the latching relay with other monitoring sources ie the total voltage of the system. You really need to control on total voltage so a BMV battery monitor or a 12V monitoring board ex amazon will still require the interface MP was offering. Not sure if your cell monitor does overall voltage.

Are you happy the 100A latching relay is big enough?

[MtB]

1 hour ago, Dr Bob said:

The drawback of your choice of the cell monitor (that will work with the latching relay) and the latching relays, is that you will still have a problem if you try and use the latching relay with other monitoring sources ie the total voltage of the system. You really need to control on total voltage so a BMV battery monitor or a 12V monitoring board ex amazon will still require the interface MP was offering.

 

Which leads me directly into the next of my stream of questions about your installation.

 

I'm not sure I buy your point about needing control on total voltage (if by that you mean a disconnect if total voltage runs too high or too low), because I'll have individual cell monitoring. In any situation where total bank voltage is too high, there will be at least one cell above the individual cell high voltage disconnect threshold and disconnect will occur anyway, and vice versa at the low end, so what purpose does whole bank monitoring serve?

 

I can see that it could serve as a coarser resolution of backup disconnect should the individual cell level disconnects fail to work, but on your system the weakest link is the common electric switch, operated by both your cell monitoring and by your total voltage monitoring by the BMV.  

 

 

 

1 hour ago, Dr Bob said:

Are you happy the 100A latching relay is big enough?

 

100A at 24V is PLENTY to run my fridge, a water pump and a few lights!

 

 

(Hopefully  )

[peterboat]

I go out to watch a film and have a few bevies and this whole thread gets ever more complex!! However I am sure between you a cheap drop in system will be deigned and for sale shortly, just dont try to sell me one my system works just fine for me

[MtB]

 

 

 

1 hour ago, Dr Bob said:

Not sure if your cell monitor does overall voltage.

 

No it doesn't, instead it has a third latching relay output triggered at 0.3v higher than whatever I set the max cell voltage and 0.3v lower than whatever I set the min cell voltage to. I guess they are thinking along the same lines as me in post 157, that this gives better protection than total voltage monitoring. In this case though, the weak link is the GWL-CPM board in the first place!

 

 

[MtB]

6 minutes ago, peterboat said:

I go out to watch a film and have a few bevies and this whole thread gets ever more complex!! However I am sure between you a cheap drop in system will be deigned and for sale shortly, just dont try to sell me one my system works just fine for me

 

Well Dr Bob and I both understand perfectly what we are both droning on about, and it is the process of arriving at a simplified method of bare cell management that will suit a large proportion of would-be lithium users. 

 

The problem with your system is your system is proprietary and the manufacturer won't spill the beans and tell you exactly what the BMS is doing inside each battery, or sell you the BMS system that connects them all together. So you can never really understand what is going on under the hood. Even though it works for you, it might not for another boater.

 

 

[Dr Bob]

1 hour ago, Mike the Boilerman said:

 

100A at 24V is PLENTY to run my fridge, a water pump and a few lights!

 

 

 

Ah, 24V. Ok.

 

 

[WotEver]

1 hour ago, Mike the Boilerman said:

In any situation where total bank voltage is too high, there will be at least one cell above the individual cell high voltage disconnect threshold

Agreed 100%. 

[Dr Bob]

1 hour ago, Mike the Boilerman said:

 

I'm not sure I buy your point about needing control on total voltage (if by that you mean a disconnect if total voltage runs too high or too low), because I'll have individual cell monitoring. In any situation where total bank voltage is too high, there will be at least one cell above the individual cell high voltage disconnect threshold and disconnect will occur anyway, and vice versa at the low end, so what purpose does whole bank monitoring serve?

 

The thing with total voltage control is that you can set it to a higher resolution ie 13.8V, 13.9V or 14.0V. At the cell level you may only be able to set it 3.4V, 3.5V or 3.6V.

If I was after a cheap system, I would forgo the cell control and just have the total voltage done by BMV or a cheap amazon board and limit charge to a 13.8V (maybe 80% SoC). For £25 add in a cell voltage meter so you can see the cell voltages and sound an alarm if one goes high (or low). For your 24V system you will have even higher resolution on total voltage.

Peter is right in what he is saying ....if you keep to <80% SoC so down around 13.7V max, you dont need to worry about cell voltages.

In practice each morning I glance at the total voltage and know exactly where I am on charge ie 12.8V is low and 13.2V is high so much easier than seeing 8 individual cell voltages. Total voltage is what I am used to.

[WotEver]

1 minute ago, Dr Bob said:

In practice each morning I glance at the total voltage and know exactly where I am on charge ie 12.8V is low and 13.2V is high so much easier than seeing 8 individual cell voltages. Total voltage is what I am used to.

A simple voltmeter will achieve the same result without needing to have any complexity whatsoever. 

[WotEver]

5 minutes ago, Dr Bob said:

The thing with total voltage control is that you can set it to a higher resolution ie 13.8V, 13.9V or 14.0V. At the cell level you may only be able to set it 3.4V, 3.5V or 3.6V.

But in practical terms, will it actually make any difference? 

[peterboat]

57 minutes ago, Mike the Boilerman said:

 

Well Dr Bob and I both understand perfectly what we are both droning on about, and it is the process of arriving at a simplified method of bare cell management that will suit a large proportion of would-be lithium users. 

 

The problem with your system is your system is proprietary and the manufacturer won't spill the beans and tell you exactly what the BMS is doing inside each battery, or sell you the BMS system that connects them all together. So you can never really understand what is going on under the hood. Even though it works for you, it might not for another boater.

 

 

I do know, they are all balanced and I know that because when I last checked them with the puter months years ago they were fine...........................I have however checked them on my truck and that works harder than my boat batteries and they are all linked, all balanced and cells balanced as well. so i will check them next year just to make sure they are ok? Seriously Mike these batteries are top spec which is why they are expensive secondhand

[WotEver]

So he’ll be setting his limit at say 84% instead of 80%. Or maybe 78% instead of 80%. Does it really matter?

1 minute ago, WotEver said:

But in practical terms, will it actually make any difference? 

 

[Dr Bob]

1 hour ago, Mike the Boilerman said:

I can see that it could serve as a coarser resolution of backup disconnect should the individual cell level disconnects fail to work, but on your system the weakest link is the common electric switch, operated by both your cell monitoring and by your total voltage monitoring by the BMV. 

 

Yes, the weakest link is the motorised switch but that is the last line of defence as it is only used in the event of other equipment failure as the charging devices cut off before the critical voltage points. Having both total voltage (cheap to do) and cell level monitoring you get multiple layers of redundancy. So in my system it is:

 

- at 13.6V the alternator cuts voltage and amps

- at 13.7V the total voltage device sounds audible alarm (I SHOULD TAKE ACTION)

- at 13.9V the total voltage device isolates the Li bank (normally if the cells are in balance then the cell level monitoring will not be at the trigger point

- at a higher voltage the alarm will sound on the cell monitor (ACTION MUST BE TAKEN).....and on the cell voltage meter.

- at 3.8V on any cell the device isolates the bank

 

If the motorised valve fails on the total voltage, I will know if the cell alarm goes.

 

This will only happen with the engine running and for me the only risk of not being on the boat is if I was in a lock flight and off the boat. Over the past 6 months we have never been in a lock flight when above 80% SoC. I would notice if the alternator hadnt cut its charge in the first step.

Edited October 24, 2019 by Dr Bob

[Dr Bob]

6 minutes ago, WotEver said:

But in practical terms, will it actually make any difference? 

Well yes.

If the cells are balanced, if they all reach 3.400V at the same time, that is 13.6V. If set at 3.500V that is 14.0V. If one is slightly high then if you set at 3.4V, then the total bank could be 13.5V or lower which is a bit low.

I prefer to have the flexibilty to set my cut off at 13.8V or 13.9V as it fits my charge sources better. Each set up will be different.

Reacting to total voltage is cheaper than cell voltage. Do you really need to spend £80 or £130 on a cell monitoring board? For a cheap solution, I dont think it is necessary.

 

[WotEver]

2 minutes ago, Dr Bob said:

If the cells are balanced...

Perhaps Mike will find the same as you and Peter and see that they do stay balanced. Perhaps he won’t. At least he’ll know on a daily basis and I’m sure he’ll report back here with his findings. 

[Dr Bob]

Just now, WotEver said:

Perhaps Mike will find the same as you and Peter and see that they do stay balanced. Perhaps he won’t. At least he’ll know on a daily basis and I’m sure he’ll report back here with his findings. 

I would definitely have a cell voltage meter.

Something like this

https://www.hobbyrc.co.uk/isdt-bg-8s-battery-checker

That's the one I am using. £25. I am thinking the £80 I spent on the cell voltage control board was just a nice to have as it has never been needed. Belt and braces.

[MtB]

1 hour ago, WotEver said:

Perhaps Mike will find the same as you and Peter and see that they do stay balanced. Perhaps he won’t. At least he’ll know on a daily basis and I’m sure he’ll report back here with his findings. 

 

Given Peter always seems to focus on cell balance when discussing BMSs and his are always balanced, yet users of bare cells report they drift, I'm wondering if the 'BMS' built into each of Peter's batteries is actually a cell balancing device. E.g. something like this device mentioned by Tom and Bex:

 

https://www.ebay.co.uk/itm/254003975899?ul_noapp=true

 

 

 

Once the cells can be relied upon always to be balanced, then whole bank voltage becomes the only parameter that needs monitoring for disconnection if necessary. And this can be done with the Victron BMV-702 which most peeps will already have, Moomin's planned latching relay drive module and a latching relay. Either the £10 120A relay from GWL or the £60 190A relay from RS.

 

 

 

 

 

[peterboat]

45 minutes ago, Mike the Boilerman said:

 

Given Peter always seems to focus on cell balance when discussing BMSs and his are always balanced, yet users of bare cells report they drift, I'm wondering if the 'BMS' built into each of Peter's batteries is actually a cell balancing device. E.g. something like this device mentioned by Tom and Bex:

 

https://www.ebay.co.uk/itm/254003975899?ul_noapp=true

 

 

 

Once the cells can be relied upon always to be balanced, then whole bank voltage becomes the only parameter that needs monitoring for disconnection if necessary. And this can be done with the Victron BMV-702 which most peeps will already have, Moomin's planned latching relay drive module and a latching relay. Either the £10 120A relay from GWL or the £60 190A relay from RS.

 

 

 

 

 

Thats the issue Mike, Valence say the board in the battery requires a BMS to control it Geeks from the USA say that if you connect the batteries together with the leads the batteries do talk to each other, all I know is that the board is live but changes when the puter is connected, however even when reaching 100% and the puter not connected the cells are well balanced, which shows when the puter is plugged in and cells are green. what this has done is give me a false sense of security, backed up by my recent check of the van, which works very hard, both in acceleration and regen, maybe the constant solar keeps them balanced? maybe its luck? or maybe valence are telling porkies and the board is a BMS which balances cells. But as I dont really know maybe I should check more often? but its a faff so I dont bother unless I am doing stuff on the batteries

By the way that listing is for LA batteries

Edited October 24, 2019 by peterboat

[Craig Shelley]

Are there any solid state solutions to this available yet?

Should be a lot cheaper and simpler than latching or motorised switches, in theory.

Would still want to have a proper switch for manual isolation though.

[WotEver]

8 hours ago, Craig Shelley said:

Are there any solid state solutions to this available yet?

Should be a lot cheaper and simpler than latching or motorised switches, in theory.

Would still want to have a proper switch for manual isolation though.

I doubt it would be cheaper to have 260A Mosfets as opposed to a relay. And I know which one I’d trust more in a fault condition.