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Cheap LiFePO4 BMS?


jetzi

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So we went out cruising the last week didnt get far as 300 ton reed bank is blocking the lock entrance at Doncaster! [so the lock keeper told me] Anyway the new speed controller is putting out much more power than the old one, and as always the solar is providing the motive and leisure power that I use. The upshot is for me quality solar controllers are a must buy with LifePo4 batteries and realistic charging voltages the only thing I care about, I look at the NASA BMV2 and I see the top number and below that amps in and out, in reality only the voltage matters. I really should put some safety features in, but as it seems to be doing ok it does seem to be pointless, its fused up and has MCBs and surge protection for the solar controllers so do I really need to do anything else? For me the Kiss principle works for others that still have ICE Nicks board will save a lot of pain and cost in the future, if I still had ICE I would be buying one

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2 hours ago, Dr Bob said:

Changing the topic slightly, I thought I would update you on my re-install of my Lifepo4s on my new boat – rather than start a new thread.

For those of you keeping up, you will remember I had my 480Ahrs of Lifepo4s in parallel with the 660ahrs of LAs on my last boat. These were removed in March as we prepared to sell the boat leaving the LA's intact and fully operational. I now have a newly built boat and am installing the Li's as per the old boat with some subtle differences. The new boat came with 480Ars of AGMs, a 240A alternator (and a 50A one) and a Victron Quattro 5K combi thingy. One limitation is not to mess too much with the warranty on the new boat so taking the alternator apart is not an option for 12 months – but then it will be! (Nick, I am watching your progress closely!!).

So, the set up is that I am putting the 480Ahrs of Li's in parallel with the LA's but using a pair of Sterling 60A BtoB's. See summary diagram below. The BMS side (battery management system – not battery monitoring system) is the same as before. I am using a BEP701-md motorised switch to isolate the Li bank in the event of over or under voltage (or temp excursions) as measured by the dedicated BMV701 and BMM8v2 (Aussi cell monitoring unit) and with multiple layers of warning alarms (now the BMV701 has had its firmware updated so we can hear the alarm!). This system has worked very well for 12 months so has proven itself.

The difference to the old boat is how it is paralleled in to the LAs. Previously I had an alternator which could be controlled to back off when over 80% full and a full controllable solar set up. Now however I have an alternator that can deliver over 200A (and it does) plus a combi box that can also do 200A – and neither have controllers with a Lithium setting.

I am therefore going with a manual arrangement of a “1 2 Switch”. It can be in the 'Off” position in which case the Li bank is isolated. This will be the position most of the time when we are on shore power and the Combi and the LAs will be doing all the duty. When off shore power – and the engine not running- the switch will be in the '2' position with the Li's directly connected to the 12V 'bus bar' therefore providing 'all' the power. On starting the engine I will turn to the '1' position so isolating the bank from the 12V LA side but opening up the feed from the two BtoB's. I have chosen 2 *60A units which should give circa 100A together (in parallel). The BtoB's have a number of charge profiles including a 'custom' but I am starting on the AGM1 setting which gives 14.1V/13.75V/13.40V for bulk/conditioning/float. As the Li's have circa 4M of 50mm cable, there is a drop of around 0.2V down the line so although the BtoB will charge to 14.1V in bulk/abs, the Li's will only be at 13.9V (this is the way it worked on the old boat). The BtoB's should therefore reduce the voltage when I am at 80-90% full. If this doesnt work, then I can move to a custom setting. I was used to charging only at 30-40A and it may be that I need to go to higher voltages for bulk/abs if I am charging between 50A and 100A. It should be possible to therefore charge with the engine running without the emergency disconnect being activated.

As I am expecting to get 100A with the 2 BtoBs, they will likely be taking 120A from the alternator which should be OK for temperature. That is something to keep an eye on but the BtoB's have a setting to reduce to half power or turn one off (and one has an isolation switch) – so I have the option to charge at 25A, 50A, 75A or 100A with the alternator.

I have so far checked the system out with the combi box firing up one of the BtoBs (need to wire the other one in yet) and that was putting in 45A in.

So the only manual intervention is to set the '1 2 switch' to '1' setting before we start the engine and then turn it back to '2' when we stop it. If we forget and start the engine in the '2' position – ie direct to the LAs, then the alternator is likely to be putting 150A plus into the Li's and we will soon notice as I ALWAYS check the alternator is putting power in when we start the engine. I could automate this with a motorised 1 2 switch but happy to test it all out this way.

Anyone got any comments on the set up? Have I missed anything? I am not that well up on the BtoB's so not sure how they operate other than what is in the manual. There are no dire warnings in the manual on turning the power on/off to the unit or if the Li's isolate via the motorised switch so I assume they are robust to that. Any inputs?

 

 

 

lifepo4 layout S'A'Chroin.png

Very pretty diagram!
 

I dunno, it just seems very complicated to me. I will just have the Lithiums connected to alternator connected to Combi, with a BMS to monitor cell voltages and adjust alternator and Combi charge voltage and current, built in balancing, audio alarm  and control of the one Tyco relay which will disconnect the lithiums if something goes majorly tits up or I discharge too much.

 

The component cost for each of the 2 boards will probably be around £50. Plus a lot of my time, of course, but that is free in Lockdown!

 

I think the fundamental difference between our approaches is that you are adding expensive kit to compensate for the inability to control the power sources, whereas I am controlling the power sources directly.

 

Oh and surely the 250A fuse, relays and switch are much too small for a 5kva Combi? 

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Oh and also re the 1-2 switch if this is a battery selector switch they are usually make before break. If that could result in the output of the BMS being directly connected to the input, that might be a bad thing (not sure). Or is the off position between 1 and 2?

Edited by nicknorman
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6 hours ago, nicknorman said:

Very pretty diagram!
 

I dunno, it just seems very complicated to me. I will just have the Lithiums connected to alternator connected to Combi, with a BMS to monitor cell voltages and adjust alternator and Combi charge voltage and current, built in balancing, audio alarm  and control of the one Tyco relay which will disconnect the lithiums if something goes majorly tits up or I discharge too much.

 

The component cost for each of the 2 boards will probably be around £50. Plus a lot of my time, of course, but that is free in Lockdown!

 

I think the fundamental difference between our approaches is that you are adding expensive kit to compensate for the inability to control the power sources, whereas I am controlling the power sources directly.

 

 

Oh, I fully agree but I am constrained somewhat in wanting to maintain the warranty on as much as I can - and the build it yourself component route does require major surgery on the alternator. The short term fix is to buy off the shelf stuff and not need the skill to build the controller. In a years time when the warranty is up then I will buy a new alternator and hopefully try one of your solutions!

 

6 hours ago, nicknorman said:

 

Oh and surely the 250A fuse, relays and switch are much too small for a 5kva Combi? 

I did think long and hard about this so good you have brought it up. We will never run 5KVA but may get to 3KW which is why we didnt go for the 3KVA one. The motorised switch and 1 2 switch are both rated at 300A continuous so the 250 A fuse should go first. There are 50mm cables to the Li's....about 5 metres of cable each for black and red. The Quattro is wired to the LA's via 2*90mm cables. If we put a couple of things on which would draw 250A -300A then power will flow from both banks of batteries. There is always a good 'surface charge' on the LA's as the voltage is usually 12.9-13.2V and you always saw discharge from the LAs when there was a big draw on our old boat. The 2*90mm to the LAs and 1* 50mm cable to the Li's should mean power also flows from the LAs. I will check this out when we get up and running. We are always careful on running high power 240V kit so not likely to exceed 3 KW.

 

6 hours ago, nicknorman said:

Oh and also re the 1-2 switch if this is a battery selector switch they are usually make before break. If that could result in the output of the BMS being directly connected to the input, that might be a bad thing (not sure). Or is the off position between 1 and 2?

Yes they are normally make before break but this one has position 1 and position 2 separated by off so I am happy that point is ok.

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12 hours ago, ivan&alice said:

Per cell or across the whole 12V battery?

That's the whole battery, but the measurement point is not right at the battery terminals. It is at the "bus-bars", the junction points of the 3 packs. These are connected with about 1m of 50mm2 wire to each of the 6 terminals.

The cells are connected using the proper links, all connections polished before tightening the bolts etc... I would say the majority of that drop will be from the cells rather than the wiring. 

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2 minutes ago, Dr Bob said:

Oh, I fully agree but I am constrained somewhat in wanting to maintain the warranty on as much as I can - and the build it yourself component route does require major surgery on the alternator. The short term fix is to buy off the shelf stuff and not need the skill to build the controller. In a years time when the warranty is up then I will buy a new alternator and hopefully try one of your solutions!

 

I did think long and hard about this so good you have brought it up. We will never run 5KVA but may get to 3KW which is why we didnt go for the 3KVA one. The motorised switch and 1 2 switch are both rated at 300A continuous so the 250 A fuse should go first. There are 50mm cables to the Li's....about 5 metres of cable each for black and red. The Quattro is wired to the LA's via 2*90mm cables. If we put a couple of things on which would draw 250A -300A then power will flow from both banks of batteries. There is always a good 'surface charge' on the LA's as the voltage is usually 12.9-13.2V and you always saw discharge from the LAs when there was a big draw on our old boat. The 2*90mm to the LAs and 1* 50mm cable to the Li's should mean power also flows from the LAs. I will check this out when we get up and running. We are always careful on running high power 240V kit so not likely to exceed 3 KW.

 

Yes they are normally make before break but this one has position 1 and position 2 separated by off so I am happy that point is ok.

Just to clarify on the alternator thing, whilst I can’t speak for your model, there was no real “major surgery” required for mine. The brushes and regulator were in 1 housing held on by 2 screws plus a third for an electrical connection to D+. I simply got a replacement brush/regulator module from ebay for about £15 on which I did the “major surgery” ie snipped the 3 wires to the regulator, and added 1 wire to ground one of the brushes. The wire from my regulator connects to the other brush.

 

So to swap between the standard setup and my setup requires the plastic cover over the back of the alternator to be removed, and the 3 screws undone to remove the brush/reg module and replace it with the other one. Not that I am now expecting ever to have to re-fit the original brush/reg module, but it remains a 5 minute job. Well as it happens, it was too awkward to do it with the alternator in situ so to the 5 mins add the time it takes to remove and replace the alternator, just to get access.

 

1 2 switch you have labelled as 200A but if it’s 300A that is better!

 

Yes I appreciate that there is no intention to use 5kva but that doesn’t mean it won’t happen! I am reminded of one of the first times we had Jeff’s parents on board. His mother trying to be helpful at breakfast, with one sweep of her hand and before I could scream, turned on the 2kw electrics kettle, the Nespresso coffee machine (about 1.6 kw IIRC) and the toaster (950w). Our 2500va Mastervolt didn’t much like that!
 

So you’d better have a couple of spare 250A fuses!

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3 minutes ago, nicknorman said:

Just to clarify on the alternator thing, whilst I can’t speak for your model, there was no real “major surgery” required for mine. The brushes and regulator were in 1 housing held on by 2 screws plus a third for an electrical connection to D+. I simply got a replacement brush/regulator module from ebay for about £15 on which I did the “major surgery” ie snipped the 3 wires to the regulator, and added 1 wire to ground one of the brushes. The wire from my regulator connects to the other brush.

 

So to swap between the standard setup and my setup requires the plastic cover over the back of the alternator to be removed, and the 3 screws undone to remove the brush/reg module and replace it with the other one. Not that I am now expecting ever to have to re-fit the original brush/reg module, but it remains a 5 minute job. Well as it happens, it was too awkward to do it with the alternator in situ so to the 5 mins add the time it takes to remove and replace the alternator, just to get access.

 

 

Yes, I agree but I'm keen not to muck about with the new alternator until out of the boat builders warranty. I will look into how to do this on my alternator next year.

Yes the 1,2 switch is 300A. Typo on the diagram.

5 minutes ago, nicknorman said:

 

Yes I appreciate that there is no intention to use 5kva but that doesn’t mean it won’t happen! I am reminded of one of the first times we had Jeff’s parents on board. His mother trying to be helpful at breakfast, with one sweep of her hand and before I could scream, turned on the 2kw electrics kettle, the Nespresso coffee machine (about 1.6 kw IIRC) and the toaster (950w). Our 2500va Mastervolt didn’t much like that!
 

So you’d better have a couple of spare 250A fuses!

Mrs Bob is well trained and we only have a Nespresso and a hair dryer that uses high Amps without the engine running. All other high usage kit (an 'instant pot' and the washing machine) are only used with the engine running. We try and avoid guests!!!!!

I have one spare 250A fuse. I'll see how it goes.?

Thanks for the inputs. All very useful.

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14 minutes ago, nicknorman said:

Oh and not wanting to spoil your day but the last word of the mountain after which your new boat seems to be named, is normally spelt Chroin. Hopefully a typo on the forum not on the boat?

Yes, it was also spelt wrong on my CRT license but corrected last week when we got the sign writer out.  Hadn't noticed it was also wrong in my profile! At least it's right on the side of the boat.

......and at least someone knows where the name comes from.

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10 hours ago, Dr Bob said:

Yes, it was also spelt wrong on my CRT license but corrected last week when we got the sign writer out.  Hadn't noticed it was also wrong in my profile! At least it's right on the side of the boat.

......and at least someone knows where the name comes from.

One of our long standing members of the gliding club had the good idea of inventing a competition to overfly as many Munros as possible. There is a per-year total and an overall total. It is a great competition because obviously it gets harder the further away from airfield a Munro is. The more you get, the more precise you have to be  (I have to get within 100m of the summit)
 

I have turned Aberfeldy and done most of the Munros between there and the top of Loch Lomond, so probably done that one but can’t check here on the boat. And by the way, getting there by the power of the atmosphere is much easier than having to walk up it!

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  • 3 weeks later...

Top balancing my cells by following Will Prowse's method in this vid: youtube.com/watch?v=x5ABvbbics8

 

I.e. connect the 16 cells in parallel, then using a lab power supply set to 3.6V at full current, and wait for the current to drop to zero.

 

I connected the cells and set up the power supply to 3.6V with minimal current. As soon as I connected the battery the voltage dropped to 3.3V (the voltage of my battery). I set the current to max and it shows 5.05A at 3.3V. My uni-t confirms both numbers.

 

My understanding is that the voltage of the whole system under charge should be at 3.6V? I can't seem to raise this voltage by twiddling the knobs.

 

I imagine this is going to take a very long time, which is fine, but is it going to work at all?

IMG_20200815_155711.jpg

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4 minutes ago, ivan&alice said:

Top balancing my cells by following Will Prowse's method in this vid: youtube.com/watch?v=x5ABvbbics8

 

I.e. connect the 16 cells in parallel, then using a lab power supply set to 3.6V at full current, and wait for the current to drop to zero.

 

I connected the cells and set up the power supply to 3.6V with minimal current. As soon as I connected the battery the voltage dropped to 3.3V (the voltage of my battery). I set the current to max and it shows 5.05A at 3.3V. My uni-t confirms both numbers.

 

My understanding is that the voltage of the whole system under charge should be at 3.6V? I can't seem to raise this voltage by twiddling the knobs.

 

I imagine this is going to take a very long time, which is fine, but is it going to work at all?

IMG_20200815_155711.jpg

I am building a bank for my electric car, they are lithium polymer 4.2 volts per cell, 3 packs of 75 cells 5P x 15S. I have bought 3 battery balancing boards rather than BMSs, I could not find a good enough BMS at a reasonable price for the job. The board is a power transfer type rather than resistor version it balance at up to 5 amps 

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6 minutes ago, ivan&alice said:

It has just clocked over to 3.4V, so it is clearly working. Great!

Yup, you’re drawing more power than it can provide so it’s voltage limiting itself right now. As you state that you’ve twiddled the knobs since the batteries have been connected I suggest you disconnect it in order to correctly set the voltage again. 

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1 hour ago, ivan&alice said:

Top balancing my cells by following Will Prowse's method in this vid: youtube.com/watch?v=x5ABvbbics8

 

I.e. connect the 16 cells in parallel, then using a lab power supply set to 3.6V at full current, and wait for the current to drop to zero.

 

I connected the cells and set up the power supply to 3.6V with minimal current. As soon as I connected the battery the voltage dropped to 3.3V (the voltage of my battery). I set the current to max and it shows 5.05A at 3.3V. My uni-t confirms both numbers.

 

My understanding is that the voltage of the whole system under charge should be at 3.6V? I can't seem to raise this voltage by twiddling the knobs.

 

I imagine this is going to take a very long time, which is fine, but is it going to work at all?

IMG_20200815_155711.jpg

 

Initially, when connecting a less than fully charged  battety the power supply cannot provide the voltage requested. This is because the current required to charge the batteries is more than the power supply's power rating (volts x amps). 

 

As the battery charges, less current is drawn and so the voltage will rise to the set point.

 

Damn, Wotever got there firdt. As he says, check the voltage setting again if you have moved the knob.

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1 minute ago, nicknorman said:

Did I mention I’ve ordered 12 x 200Ah CALB cells from China? Jolly exciting, except I have to wait 30-50 days for them☹️

Well Nick at last you are entering the lithium world! It's going to be a substantial bank for the boat 

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3 minutes ago, peterboat said:

Well Nick at last you are entering the lithium world! It's going to be a substantial bank for the boat 

Unfortunately there is still absolutely nothing wrong with the 450Ah of Trojans. I will have to find a need to repurpose them! I am certainly not going to do any sort of girly half and half system.

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7 minutes ago, nicknorman said:

Unfortunately there is still absolutely nothing wrong with the 450Ah of Trojans. I will have to find a need to repurpose them! I am certainly not going to do any sort of girly half and half system.

Flog them on here?

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2 hours ago, nicknorman said:

Did I mention I’ve ordered 12 x 200Ah CALB cells from China? Jolly exciting, except I have to wait 30-50 days for them☹️

Fantastic nick! Looking forward to hearing about your install.

 

4 hours ago, WotEver said:

Yup, you’re drawing more power than it can provide so it’s voltage limiting itself right now. As you state that you’ve twiddled the knobs since the batteries have been connected I suggest you disconnect it in order to correctly set the voltage again. 

 

3 hours ago, cuthound said:

Initially, when connecting a less than fully charged  battety the power supply cannot provide the voltage requested. This is because the current required to charge the batteries is more than the power supply's power rating (volts x amps). 

 

As the battery charges, less current is drawn and so the voltage will rise to the set point.

Makes sense. I just thought perhaps it would work like my alternator or MPPT which raises the voltage of the battery while it is charging.

 

However I don't think this is going to work. The battery (16x 160Ah cells in parallel) is 2560Ah at 3.2V. Even if the cells are currently at 80% SoC that means I have to put 512Ah into them - or 100 hours at 5A. This also feels like altogether too much time to keep the cells at a near full SoC.

 

I really didn't want to set it up to charge at 12V battery but I think I may have to do that to get it to full in a reasonable amount of time...

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6 minutes ago, ivan&alice said:

However I don't think this is going to work. The battery (16x 160Ah cells in parallel) is 2560Ah at 3.2V. Even if the cells are currently at 80% SoC that means I have to put 512Ah into them - or 100 hours at 5A. This also feels like altogether too much time to keep the cells at a near full SoC.

 

I really didn't want to set it up to charge at 12V battery but I think I may have to do that to get it to full in a reasonable amount of time...

The only other way of doing it is to connect the cells in parallel then series to make a 12v battery, charge as that and monitor each set of paralleled cells and apply high power resistors to the three sets of cells at the highest voltage to shunt current into the lowest set of cells. Then disconnect the resistors one by one as their cells reach the voltage of the lowest cell.

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31 minutes ago, ivan&alice said:

However I don't think this is going to work. The battery (16x 160Ah cells in parallel) is 2560Ah at 3.2V. Even if the cells are currently at 80% SoC that means I have to put 512Ah into them - or 100 hours at 5A.

Yes. To put it another way, your psu appears to be a 15W device and you have to put around 1600W into the cells. Somewhere in excess of 100 hours. 

21 minutes ago, nicknorman said:

The only other way of doing it is to connect the cells in parallel then series to make a 12v battery, charge as that...

Even then, even with a 50A charger he’ll be looking at around 30 hours charging time. 

Edited by WotEver
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