Cheap LiFePO4 BMS?

[eid]

3 minutes ago, Richard10002 said:

If LiFePo4 batteries survive for the number of cycles predicted, they are actually incredibly cheap.

 

I am toying* with paying £1500 for a 300Ah system which, if it survives for 5000 cycles, and I cycle it every 3 days on average, I think they will last for about 40 years, (I will be either 99 or dead, ast the end of their life   ). At £300 every 2 or 3 years, for your cheapo disposables, you will spend £1500 in 10 to 15 years.

 

The calculation obviously relies on you being young enough to survive long enough to make the economies work, and not destroying the batteries.

 

Only toying  

 

And this doesn't take into account the endless hours running an engine to charge LA to 1% tail current. This alone makes it worth it for me.

[Richard10002]

3 hours ago, eid said:

The ebay seller has relisted them showing the cycles on each. I have bought a couple and intend doing exactly as above. We'll see how it goes ?

Have you bought the two with less than 200 cycles used? There is no doubt that they will be good value if you can avoid damaging them.

 

I saw them but had already decided against them. All the info on them says that they should be connected to a BMS. Peter says that, "being careful with voltage" means they are OK, but I didnt fancy the risk, (as I saw it).

 

In the scheme of things, even if I spend £1500 on a brand new 300Ah system, it should last me between 25 and 40 years, and it will be interesting to start with. If I can find used like the Winstons discussed earlier, even better  

[eid]

15 minutes ago, MoominPapa said:

The point is that if you charge to a cut-off voltage of (say) 14.0v and then terminate the charge, then your battery will have a lower SoC at termination if you have 100A alternator than if you have a 50A alternator. Adding to the complication is the transfer curve of the alternator regulator: some are very sharp and leave the alternator at maximum output until the voltage is very close to the set-point. Some start to throttle back alternator current (actually excitation current) half a volt or more before the setpoint.

 

The equation of a set-point voltage with a limit SoC is _very_ approximate.

 

MP. 

So would this work as a testing regime, in order to establish what voltage needs to be the cut-off with each alternator:

 

1. Discharge bank somewhat e.g. 50%
2. Charge to 13.9V
3. Disconnect charge source
4. Read rested voltage
5. If rested voltage is < 13.3V (90 SOC) then..
6. Charge to 0.1V more.
7. Goto 3

Edited November 3, 2019 by eid

[Richard10002]

4 minutes ago, eid said:

 

And this doesn't take into account the endless hours running an engine to charge LA to 1% tail current. This alone makes it worth it for me.

Agreed... I did that sum earlier today, and figured a saving of about £300 a year in petrol for the genny, assuming 6 months of genny running, and 6 months of solar.

 

So I should save my £1500 in 5 years on fuel alone.

 

It's pretty much a no brainer assuming that we can avoid destroying the batteries. Given that I have killed 4 sets of LA batteries in 8 years, I'm a bit wary of doing the same to Lithiums  

[eid]

15 minutes ago, Richard10002 said:

Agreed... I did that sum earlier today, and figured a saving of about £300 a year in petrol for the genny, assuming 6 months of genny running, and 6 months of solar.

 

So I should save my £1500 in 5 years on fuel alone.

 

It's pretty much a no brainer assuming that we can avoid destroying the batteries. Given that I have killed 4 sets of LA batteries in 8 years, I'm a bit wary of doing the same to Lithiums  

 

Did you notice my earlier post regarding the ebay seller you mentioned?

 

EDIT: Sorry, I didn't notice your post above addressing this.

 

Edited November 3, 2019 by eid

[MoominPapa]

1 minute ago, eid said:

So would this work as a testing regime (using 90 amp alternator):

 

1. Discharge bank somewhat e.g. 50%
2. Charge to 13.9V
3. Disconnect charge source
4. Read rested voltage
5. If rested voltage is < 13.3V (90 SOC) then..
6. Charge to 0.1V more.
7. Goto 5

No idea. It depend on the transfer curve of the alternaor regulator, and the capacity of the bank, at least. To get to fully charged, the usual approach is to continue charging, reducing current as necessary to avoid overvoltage, until the terminal voltage exceeds 13.9 or 14.0v AND the current is less that 0.05C AT THE SAME TIME.

 

MP.

 

 

 

 

[peterboat]

10 minutes ago, Richard10002 said:

Have you bought the two with less than 200 cycles used? There is no doubt that they will be good value if you can avoid damaging them.

 

I saw them but had already decided against them. All the info on them says that they should be connected to a BMS. Peter says that, "being careful with voltage" means they are OK, but I didnt fancy the risk, (as I saw it).

 

In the scheme of things, even if I spend £1500 on a brand new 300Ah system, it should last me between 25 and 40 years, and it will be interesting to start with. If I can find used like the Winstons discussed earlier, even better  

Richard I have been doing this for a year on two banks of these and had no issues, those leads you see dangling can be connected to the puter and you can see the BMS working in the battery I have posted videos of this in the past. Now my new batteries are Valence as well 36 volt ones, some were showing 2.7 volts when acquired cheaply! They happily charged up the BMS was reset and they are holding 40 volts plus after a couple of months. So are they that fragile? these have been in buses working hard and yet they took in nearly all of the KWHs they were designed for

[eid]

1 minute ago, MoominPapa said:

No idea. It depend on the transfer curve of the alternaor regulator, and the capacity of the bank, at least. To get to fully charged, the usual approach is to continue charging, reducing current as necessary to avoid overvoltage, until the terminal voltage exceeds 13.9 or 14.0v AND the current is less that 0.05C AT THE SAME TIME.

 

MP.

 

 

 

 

But can you rely on the same alternator/bank to produce the same result each time?

[MoominPapa]

2 minutes ago, eid said:

But can you rely on the same alternator/bank to produce the same result each time?

There might be temperature effects, but apart from that, yes. The main source of noise is the variation of domestic loads happening at the same time as the charging; fridge, washing machine etc.

 

MP.

 

[eid]

25 minutes ago, Richard10002 said:

Have you bought the two with less than 200 cycles used? There is no doubt that they will be good value if you can avoid damaging them.

 

I saw them but had already decided against them. All the info on them says that they should be connected to a BMS. Peter says that, "being careful with voltage" means they are OK, but I didnt fancy the risk, (as I saw it).

 

In the scheme of things, even if I spend £1500 on a brand new 300Ah system, it should last me between 25 and 40 years, and it will be interesting to start with. If I can find used like the Winstons discussed earlier, even better  

I bought 2 at ~ 600 cycles as they were cheaper and I didn't think the difference was worth it. I have read from Peter and seen on you-tube people saying that these batteries have an internal BMS of some sort which at the very least balances the cells. That will do for me.

 

Time will tell if I made the right choice ?

[peterboat]

I will see if I can find the videos of the batteries in charging and discharging mode and post it again for all you potential valence users

[eid]

2 minutes ago, peterboat said:

I will see if I can find the videos of the batteries in charging and discharging mode and post it again for all you potential valence users

I remember that video. Your dirty screen gave me anxiety ?

5 minutes ago, eid said:

 seen on you-tube people saying that these batteries have an internal BMS of some sort which at the very least balances the cells

Speaking of which, people might find this interesting:

 

 

[WotEver]

1 hour ago, eid said:

So would this work as a testing regime, in order to establish what voltage needs to be the cut-off with each alternator:

 

1. Discharge bank somewhat e.g. 50%
2. Charge to 13.9V
3. Disconnect charge source
4. Read rested voltage
5. If rested voltage is < 13.3V (90 SOC) then..
6. Charge to 0.1V more.
7. Goto 3

I think your #6 might be a bit coarse. In your initial experiments I’d suggest raising the voltage by 0.01 or 0.02V. It might take longer to get there but it would be safer. 

[eid]

28 minutes ago, WotEver said:

I think your #6 might be a bit coarse. In your initial experiments I’d suggest raising the voltage by 0.01 or 0.02V. It might take longer to get there but it would be safer. 

 

Thanks, I'll do that.

Edited November 3, 2019 by eid

[eid]

This is another possible scenario I've been thinking about, using the devices I have:

 

Again, 2 banks connected in parallel with an isolator between the lifepo4's and the LA.

 

The Victron BMV-712 relay has 3 connections and is a 3 way switch.

1. Normally Open (NO)
2. Com
3. Normally Closed (NC)

(The relays default state can be chosen in the settings)

 

The relay switches between Com>NO and Com>NC. (when the relay is set at open, there is a circuit between Com and NC. When it is switched to closed, the circuit is made between Com and NC instead.)

 

So...

 

When the engine is started, the Victron BMV recognises the higher voltage, activates the relay, disconnecting isolator 1 (NC) and therefore the lithium bank from both charge and loads.

 

It also connects isolator 2 (NO) switching on the inverter and the Victron IP22 charger (lifepo4 charge regime).

 

When the engine is turned off, the voltage reduces on the LA bank and the BMV switches the relay back, reconnecting the lithium to the LA, and disconnecting the inverter.

 

What could go wrong?  ?

[Richard10002]

10 minutes ago, eid said:

This is another possible scenario I've been thinking about, using the devices I have:

 

Again, 2 banks connected in parallel with an isolator between the lifepo4's and the LA.

 

The Victron BMV-712 relay has 3 connections and is a 3 way switch.

1. Normally Open (NO)
2. Com
3. Normally Closed (NC)

(The relays default state can be chosen in the settings)

 

The relay switches between Com>NO and Com>NC. (when the relay is set at open, there is a circuit between Com and NC. When it is switched to closed, the circuit is made between Com and NC instead.)

 

So...

 

When the engine is started, the Victron BMV recognises the higher voltage, activates the relay, disconnecting isolator 1 (NC) and therefore the lithium bank from both charge and loads.

 

It also connects isolator 2 (NO) switching on the inverter and the Victron IP22 charger (lifepo4 charge regime).

 

When the engine is turned off, the voltage reduces on the LA bank and the BMV switches the relay back, reconnecting the lithium to the LA, and disconnecting the inverter.

 

What could go wrong?  ?

MtB has his Lithiums in parallel with his Lead Acid, with an isolator between them - more than that I dont know, but it seems to be working for him. I toyed with that, but it seemed that a close eye needs to be kept in order to know when to have the isolator open or closed.

 

I like the idea of single cells and a BMS that takes care of shutting things down, and starting them up again, as events occur, (hi and low voltages and temps, it seems).

[eid]

18 minutes ago, Richard10002 said:

MtB has his Lithiums in parallel with his Lead Acid, with an isolator between them - more than that I dont know, but it seems to be working for him. I toyed with that, but it seemed that a close eye needs to be kept in order to know when to have the isolator open or closed.

 

I like the idea of single cells and a BMS that takes care of shutting things down, and starting them up again, as events occur, (hi and low voltages and temps, it seems).

You can have the isolator open/close function controlled by a Victron BMV-712. It can activate the isolator on high/low voltage, high/low temperature or low state of charge. This is in effect a BMS except for the cell balancing function, which Valence batteries do internally (allegedly).

 

It's a shame the BMV can't activate the relay on 100% SOC as this is determined by your choice of voltage and tail current.

Edited November 3, 2019 by eid

[Dr Bob]

4 hours ago, eid said:

This is how I intend to set things up:

 

lifepo4 bank connected in parallel to a LA bank. BEP motorised switch between the LA and lifepo4, controlled by a Victron BMV-712 relay which will disconnect at low voltage, high voltage or perhaps 100% SOC (defined by voltage and current).

 

So alternator charges at 14.4V. Once lifepo4 reach 13.9V the BEP isolator disconnects them from charge and the LA bank continues to charge.

 

The BMV sensors will be attached to the LA and will reconnect the lifepo4 bank when the alternator stops sending current.

 

(This could have been better explained in a diagram I guess)

 

 

Sorry to go on about this. I just really need to understand it ?

 

Sorry I am late in responding but I think you have the answer to the 14.4V.

Volatge will rise as you charge from say 13.5V upwards. I rely on my charge sources backing down on charge as they get towards the voltage knee so the BEP switch is only there for an emergency. I am lucky that I have the AtoB to do that control. Without that you can of course use your BMV to isolate the Li bank at 13.9V (or wotever you chose) but that puts wear and tear on the switch. Will it be reliable? What you could do is use that disconnect at 13.9V but put a 2nd isolating switch activated by the cell monitoring unit as a second line of defense IF the BEP fails. Using the Tyco relay would be cheaper. Get two of them and get MP to make you up a control board.....MP, I will buy one as well!

 

 

2 hours ago, eid said:

So would this work as a testing regime, in order to establish what voltage needs to be the cut-off with each alternator:

 

1. Discharge bank somewhat e.g. 50%
2. Charge to 13.9V
3. Disconnect charge source
4. Read rested voltage
5. If rested voltage is < 13.3V (90 SOC) then..
6. Charge to 0.1V more.
7. Goto 3

I wouldn't do that.

Have you got a battery charger that works at 30A to 40A. 

If so, discharge you Li 's to 50% ish.

Put charger on and take readings. Make up a table. For each line -

Amps in, Ahrs reading, Total bank voltage, individual cell voltage, delta between high and low cells, time. 

Take readings every 5mins....less at start....more at end. Write them down!!!!!!! They will be useful next time you do it.

PM me if you want to see an example!!!!

Watch the voltage rise and the current stay pretty constant. If the bank is well balanced, as you reach 3.45V per cell, start looking every few minutes. You should start to see the current drop from 30A. Don't let an individual cell get above 3.6V. Terminate the charge if it does and balance the cells.  As the current drops to 15-20A you are fully charged and terminate the charge.....turn off the charger. Now, if you have recorded all the voltages, Amps and Ahrs used, you can see what voltage refers to 80%, 90% and 100 % SoC. You can then choose the termination voltage you want. 

Note in the above, your Ahrs may not be correct but you can write this into the table as you know how it is changing with time when you have a steady current....i.e. If you are at 30A then you know the Ahr changes by 1Ahr every 2 mins.

Quite simple really. Just watch your cell voltages don't take off and at 30A charge rate you should be around 14.0-14.1V when nearing 100%.

 

One other question raised....At 50% SoC in you Li's, your LAs will be full. You LAs will only start to be used once the voltage in the Li's drops to <12.8V which is 30% on my system. I try and avoid going that low.

 

One thing not mentioned is the danger of burning out your alternator. I avoid this by keeping the current less than 50% of rated output. MP and Tom have both burned their alternators out this year by allowing them to run at much higher rates. By charging at 14.4V, it sound like the alternator may be putting out big Amps. You must pay attention to this and make sure the temp of the alternator doesn't get too high. 90C seems to be good for me.

My AtoB has. US gel setting that is 13.7V max on my Li bank. Maybe it is a function of my wiring that the voltage on the LA bank is 13.9V. Not sure if Sterling has changed the unit.....I got mine 2 years ago. 

Edited November 3, 2019 by Dr Bob

[Dr Bob]

Oops.

You are using the Valance batteries. Wot I wrote above was for bare cell batteries. I do not know how these work on charging to 100%. Peter can you help? Can you monitor cell voltage on charging and do the isolate themselves on full charge?

Personally I would try and source bare cells i.e. Thunderskys, as you will have more control. Will th Valance batteries cope with 200-300A loads if you are using them with your start batteries? Peter doesn't have LAs in his system.

[eid]

I found this thread discussing a Niehoff A2-102 regulator which can switch between 13.8V or 14.5. Which alternator does this connect to?

Edited November 4, 2019 by eid

[eid]

8 hours ago, Dr Bob said:

One other question raised....At 50% SoC in you Li's, your LAs will be full. You LAs will only start to be used once the voltage in the Li's drops to <12.8V which is 30% on my system. I try and avoid going that low.

 

One thing not mentioned is the danger of burning out your alternator. I avoid this by keeping the current less than 50% of rated output. MP and Tom have both burned their alternators out this year by allowing them to run at much higher rates. By charging at 14.4V, it sound like the alternator may be putting out big Amps. You must pay attention to this and make sure the temp of the alternator doesn't get too high. 90C seems to be good for me.

My AtoB has. US gel setting that is 13.7V max on my Li bank. Maybe it is a function of my wiring that the voltage on the LA bank is 13.9V. Not sure if Sterling has changed the unit.....I got mine 2 years ago. 

 

 

 

Yes I had intended to cut the Li bank off at this point (I would only reach that low rarely).

 

I had forgotten about the hot alternator problem. So not only the voltage needs to be restricted, but the current too! More reading for me then..

 

9 hours ago, eid said:

This is another possible scenario I've been thinking about, using the devices I have:

 

 

What could go wrong?  ?

 

I realised this morning that this plan wouldn't work as my charger is only 15 amps.

Edited November 4, 2019 by eid

[eid]

On 22/10/2019 at 16:05, Dr Bob said:

 

Bob, may I ask how you are making these charts? What operating system/device are you using? I assume its Victron Connect?

[PeterF]

34 minutes ago, eid said:

I found this thread discussing a Niehoff A2-102 regulator which can switch between 13.8V or 14.5. Can these be fitted to any alternator or just a certain type/brand?

I do not know the answer to that. What I do know is with Balmar regulator you could set the voltage down to 13.9V and set a float at 13.2. You would need to disable the voltage regulator in the alternator to go that low. The Balmar regulator also monitors the alternator temperature and reduces field (and hence charge) current if it gets too hot. You can also limit the maximum field current to effectively derate the alternator output. You can install a relay on the ignition line to the Balmar regulator driven by the BMV to turn the alternator field current off when the BMV requests rather than needing a dump battery. However, this is getting well away from the cheap BMS idea, but if I was specifying a full Victron type system, this is how I would handle the alternator, rather than using an LA dump battery.

[eid]

15 minutes ago, PeterF said:

I do not know the answer to that. What I do know is with Balmar regulator you could set the voltage down to 13.9V and set a float at 13.2. You would need to disable the voltage regulator in the alternator to go that low. The Balmar regulator also monitors the alternator temperature and reduces field (and hence charge) current if it gets too hot. You can also limit the maximum field current to effectively derate the alternator output. You can install a relay on the ignition line to the Balmar regulator driven by the BMV to turn the alternator field current off when the BMV requests rather than needing a dump battery. However, this is getting well away from the cheap BMS idea, but if I was specifying a full Victron type system, this is how I would handle the alternator, rather than using an LA dump battery.

Not cheap at £320 but it seems to deal with all of the problems raised in an alternator based lithium install. With this, some used cells, and the necessary isolators/BMS I'd still consider this a cheap system when compared to Victrons offering.

 

[Dr Bob]

9 minutes ago, eid said:

 

Bob, may I ask how you are making these charts? What operating system/device are you using? I assume its Victron Connect?

It is information that is stored at the

https://vrm.victronenergy.com

site.

The normal way of doing this is to buy a Victron venus GX or the more expensive display (the CCGX?) and connect your BMV to it. I was going to buy the Venus GX but it was £250 (IIRC). Instead I had a spare Rasp Pi around so downloaded the Victron system to put on the Pi  and connected that up to the BMV. The Pi is on all the time, connected to the BMV and to the router so is sending data every minute to the Victron VRM site which can be accessed from anywhere. We are off the boat for a few days this week and I can log in and see the power status of my batteries from 200 miles away.

If you are more interested have a look at

 

Go to post 59 which starts to detail how I did it. I am not a whizz at programming or Pi's but still managed it. In the end I had to buy a better Pi. The Pi 2 didnt work so I ended up buying a Pi 3 for £40.