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Cheap LiFePO4 BMS?


jetzi

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I have a vague recollection that back in the days when we used to use a handheld dmm to take cell measurements. The spreadsheet we recorded the results on would sometimes indicate an anomalous reading based on the sums of the cell voltages. I think we concluded that probing the nut gave unreliable results. It's been a while since we've had to take manual measurements and my memory is a bit hazy.  Probing the terminal post propper started to cause damage to the insulating terminal covers. Then we decided enough was enough and automated the process.

 

I suspect there might be some form of thermal junction or galvanic effect between dissimilar metals at the interface of the nut and terminal threads that causes voltage measurement error on the DMM.

 

I did read somewhere (unable to find the link) that the nuts might have thread locking compound, but the fact that you've been able to rotate it suggests otherwise.

I believe the nuts are made of zinc plated steel, and the terminal post is aluminium or copper.

 

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3 hours ago, Craig Shelley said:

I have a vague recollection that back in the days when we used to use a handheld dmm to take cell measurements. The spreadsheet we recorded the results on would sometimes indicate an anomalous reading based on the sums of the cell voltages. I think we concluded that probing the nut gave unreliable results. It's been a while since we've had to take manual measurements and my memory is a bit hazy.  Probing the terminal post propper started to cause damage to the insulating terminal covers. Then we decided enough was enough and automated the process.

 

I suspect there might be some form of thermal junction or galvanic effect between dissimilar metals at the interface of the nut and terminal threads that causes voltage measurement error on the DMM.

 

I did read somewhere (unable to find the link) that the nuts might have thread locking compound, but the fact that you've been able to rotate it suggests otherwise.

I believe the nuts are made of zinc plated steel, and the terminal post is aluminium or copper.

 


yes certainly when measuring small voltages, dissimilar metals and temperatures can cause issues. In my case it was very repeatable, I measured the voltage between nut and bolt/copper strips several times, for each electrode of each of the 3 cells in the group. Every time for the 5 cells the voltage was a few mV, for the one cell it was repeatably 200mV or so during charge. When charging stopped, the 200mV gradually fell to near zero over a minute or two. And the symptoms perfectly match a (relatively) high resistance connection.
All this was repeated after I’d removed all the connections from the rogue electrode, checked for cleanliness, signs of over heating etc (there were none), partially tightened it, wiggled the mating surfaces around a bit so they rubbed against each other, then fully tightened. Identical results were then obtained.

 

I agree it seem impossible/unreasonable, but it was what it was!

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Looking at the teardown videos, I'd be worried that it might be the internal connection failing, and tightening that nut may just be a temporary fix. Definitely one to keep a close eye on and I'm not sure I'd have thought to check for voltage difference there as I can't see how that would occur. 

Edited by Tom and Bex
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24 minutes ago, Tom and Bex said:

Looking at the teardown videos, I'd be worried that it might be the internal connection failing, and tightening that nut may just be a temporary fix. Definitely one to keep a close eye on and I'm not sure I'd have thought to check for voltage difference there as I can't see how that would occur. 

Agreed. Keeping a close eye on it. So far so good… trouble is I doubt I would be able to source 1 cell, I’d need to buy 4 which would be £600 or so 😪😪

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53 minutes ago, nicknorman said:

trouble is I doubt I would be able to source 1 cell, I’d need to buy 4 which would be £600 or so 😪😪

 

 

Well if you must buy bargain basement cells....

 

A customer of mine's company sells a lot of bespoke engineering products they design themselves and have made in China. He says the Chinese are tricky to do business with until you get to understand their ethics, different from ours here in The west. Here we specify stuff, get quotes, choose a supplier to order from and expect to get what we ordered, yes? In China, they start off the same but after than a game starts, which western customers don't initially realise the Chinese often play. It's name is "Find a way (or better) a series of ways in which to breach the technical spec that the customer won't notice, and which increases their wafer-thin profit margin and makes the contract worthwhile after all". He tells me they have to strictly watch every aspect of the quality of every shipment as it comes in, and if they miss any of these cheese-paring reductions in quality and just accept them, the Chinese lose respect for them a as customer.

 

I rather suspect this happens a lot with Chinese lithium cells sold over here as there is little we as buyers can do to check the quality of the cells they send over, other than doing random tear-downs of a few cells from each palette. Obviously impractical for the end user to do, and you might have fallen victim to this practice. 

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4 hours ago, MtB said:

 

 

Well if you must buy bargain basement cells....

 

A customer of mine's company sells a lot of bespoke engineering products they design themselves and have made in China. He says the Chinese are tricky to do business with until you get to understand their ethics, different from ours here in The west. Here we specify stuff, get quotes, choose a supplier to order from and expect to get what we ordered, yes? In China, they start off the same but after than a game starts, which western customers don't initially realise the Chinese often play. It's name is "Find a way (or better) a series of ways in which to breach the technical spec that the customer won't notice, and which increases their wafer-thin profit margin and makes the contract worthwhile after all". He tells me they have to strictly watch every aspect of the quality of every shipment as it comes in, and if they miss any of these cheese-paring reductions in quality and just accept them, the Chinese lose respect for them a as customer.

 

I rather suspect this happens a lot with Chinese lithium cells sold over here as there is little we as buyers can do to check the quality of the cells they send over, other than doing random tear-downs of a few cells from each palette. Obviously impractical for the end user to do, and you might have fallen victim to this practice. 

I’m sure you are right in general. Stuff from china varies from excellent (eg an iPhone) to absolute rubbish (lots of plastic tat) and all shades on between. It was a bit of a risk going with the supplier I did, but the general impression was good. Stuff arrived on schedule, extremely well packed, no hidden taxes etc to pay. But yes I doubt the quality control was top notch, just more or less adequate. And in the context of that cell, less adequate. Still, the other 11 are doing fine and this one is now fine for the time being at least.

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6 hours ago, nicknorman said:

I’m sure you are right in general. Stuff from china varies from excellent (eg an iPhone) to absolute rubbish (lots of plastic tat) and all shades on between. It was a bit of a risk going with the supplier I did, but the general impression was good. Stuff arrived on schedule, extremely well packed, no hidden taxes etc to pay. But yes I doubt the quality control was top notch, just more or less adequate. And in the context of that cell, less adequate. Still, the other 11 are doing fine and this one is now fine for the time being at least.

I am waiting for a charger from China,  a friend of mine has lived there and sorted out my purchase fingers crossed it's a good one 

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When taking conductance measurements (or ohmic measurements of any type) never use the stainless steel hex head set screw as you always measure the additional resistance of the SS as well. The same will apply to the draw nut under the connector as again there is additional resistance. This was always one of the first things we taught when we ran training courses for BT engineers. Many just would just not believe it until they actually put a meter on a cell.

Personal I never understood why the Vasaline never affected the result but it just didn't.

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Unlike ordinary lubricating greases,which are designed to strongly adhere to metal surfaces to prevent them coming into contact,;Vaseline is a pure hydrocarbon that readily flows under pressure and does not strongly adhere to metals. It therefore allows the metal surfaces to achieve a good electrical contact while preventing atmospheric oxygen from coming into contact with the mated surfaces and oxidising them.

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19 hours ago, Ronaldo47 said:

Unlike ordinary lubricating greases,which are designed to strongly adhere to metal surfaces to prevent them coming into contact,;Vaseline is a pure hydrocarbon that readily flows under pressure and does not strongly adhere to metals. It therefore allows the metal surfaces to achieve a good electrical contact while preventing atmospheric oxygen from coming into contact with the mated surfaces and oxidising them.

 

Thanks Roaldo47 you learn something new every day.

 

Daren

 

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8 minutes ago, sueanddaren said:

 

Thanks Roaldo47 you learn something new every day.

 

Daren

 

Yes that was interesting.
So far, the rogue cell is performing fine, touch wood.  But I need to find more ways to use battery juice, we barely make a dent in the 7kWh of available energy.

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I don't claim to be an expert in lubrication, other than possibly under the definition of "expert"  mentioned by my college professor many years ago: " A person who knows the meaning of one more technical word than you do" !

 

What I know about friction and  lubrication stems mainly from lectures at college half a century ago, which started with the prof saying that the mechanism of friction in general  was poorly understood.

 

What might appear to be a smooth surface is far from flat at the microscopic level, when it will be seen to consist of random peaks and valleys. When two unlubricated surfaces are pressed together, the concentration of force at coinciding random  peaks can fuse them together, which is an explanation for the phenomenon of "stiction" , in which a larger force is required to start something moving from rest, than the force needed to keep it moving. The stiction force is needed to break the welded-together peaks. 

 

When oil is applied to a surface, 

the oil molecules in contact with the surface,  become arranged with one end sticking to the surface and the opposite end directed away from the metal surface like the bristles of a brush. The opposite ends repel each other, so when two oil-coated surfaces get close together, the mutual  repulsion of the oil molecules, which coat the entire surface, including the peaks,  make it hard for the  surfaces to come into physical (and therefore also electrical),  contact, and allow the surfaces to easily slide over each other. 

 

Later, for a work project where I needed to find out information about the electrical properties of greases, I had a meeting with a chemist who was a grease expert, and he told me about how lubricating greases are mixtures of oil and soap, the soap helping to ensure that oil stays put. Vaseline, being a pure hydrocarbon , does not contain soap, and its molecules do not behave like the molecules of oil.  Under pressure, vaseline will readily flow and allow the peaks of the metal surfaces to come into intimate contact. That is why the presence of vaseline does not have an adverse effect on electrical  contact resistance when two metals are urged into contact.

 

The beneficial effect of vaseline in making low-resistance  joints in busbars carrying high currents was discovered in the late 19th century when attempts were made to use cheaper aluminium busbars instead of copper ones. Aluminium metal is highly reactive, and on exposure to air, its surface immediately becomes coated with a layer of non-conducting aluminium oxide.  So attempting to simply bolt two aluminium busbars together will result in a high-resistance joint. It was discovered that, by coating a thick layer of vaseline over  the areas of the busbar where the joint was to be made, filing the joint areas bright through the vaseline with a coarse file, and then bolting the busbars tightly together without cleaning off  the dirty vaseline first, produced excellent low-resistance joints.

 

This jointing  method is described in a book on power engineering published in the late 1920's, the author writing that joints he had inspected  that had been made in this way more than 30 years earlier were still in use, and that the technique could also be used with advantage on copper bus bars where a really low resistance was required.  

 

And that's about the sum of my knowledge as to why, on the one hand,  vaseline is good for making low-resistance electrical joints, while on the other hand,  conventional lubricating grease needs to  be kept well away from them.  I don't suppose the laws of physics have changed that much in the past 50 years!

 

 

 

 

 

Edited by Ronaldo47
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40 minutes ago, Ronaldo47 said:

I don't claim to be an expert in lubrication, other than possibly under the definition of "expert"  mentioned by my college professor many years ago: " A person who knows the meaning of one more technical word than you do" !

 

What I know about friction and  lubrication stems mainly from lectures at college half a century ago, which started with the prof saying that the mechanism of friction in general  was poorly understood.

 

What might appear to be a smooth surface is far from flat at the microscopic level, when it will be seen to consist of random peaks and valleys. When two unlubricated surfaces are pressed together, the concentration of force at coinciding random  peaks can fuse them together, which is an explanation for the phenomenon of "stiction" , in which a larger force is required to start something moving from rest, than the force needed to keep it moving. The stiction force is needed to break the welded-together peaks. 

 

When oil is applied to a surface, 

the oil molecules in contact with the surface,  become arranged with one end sticking to the surface and the opposite end directed away from the metal surface like the bristles of a brush. The opposite ends repel each other, so when two oil-coated surfaces get close together, the mutual  repulsion of the oil molecules, which coat the entire surface, including the peaks,  make it hard for the  surfaces to coming into physical (and therefore also electrical),  contact, and allow the surfaces to easily slide over each other. 

 

Later, for a work project where I needed to find out information about the electrical properties of greases, I had a meeting with a chemist who was a grease expert, and he told me about how lubricating greases are mixtures of oil and soap, the soap helping to ensure that oil stays put. Vaseline, being a pure hydrocarbon , does not contain soap, and its molecules do not behave like the molecules of oil.  Under pressure, vaseline will readily flow and allow the peaks of the metal surfaces to come into intimate contact. That is why the presence of vaseline does not have an adverse effect on electrical  contact resistance when two metals are urged into contact.

 

The beneficial effect of vaseline in making low-resistance  joints in busbars carrying high currents was discovered in the late 19th century when attempts were made to use cheaper aluminium busbars instead of copper ones. Aluminium metal is highly reactive, and on exposure to air, its surface immediately becomes coated with a layer of non-conducting aluminium oxide.  So attempting to simply bolt two aluminium busbars together will result in a high-resistance joint. It was discovered that, by coating a thick layer of vaseline over  the areas of the busbar where the joint was to be made, filing the joint areas bright through the vaseline with a coarse file, and then bolting the busbars tightly together without cleaning off  the dirty vaseline first, produced excellent low-resistance joints.

 

This jointing  method is described in a book on power engineering published in the late 1920's, the author writing that joints he had inspected  that had been made in this way more than 30 years earlier were still in use, and that the technique could also be used with advantage on copper bus bars where a really low resistance was required.  

 

And that's about the sum of my knowledge as to why, on the one hand,  vaseline is good for making low-resistance electrical joints, while on the other hand,  conventional lubricating grease needs to  be kept well away from them.  I don't suppose the laws of physics have changed that much in the past 50 years!

 

 

 

 

 

Cheers we used vaseline in the forces for terminals on batteries, I never knew how good it was at making good conducting joints but do now

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  • 1 month later...

Thought I'd give an update on how my setup is performing after 2 years (tempting fate ?)

 

I have 3 2nd hand Valences, charged by 500w solar or 60amp Sterling BtoB.

On the whole they are performing well and I've often got more power than I know what to do with. Washing machine, immersion, kettle and toaster etc. use is limited by inverter capacity, but I'm careful not to use them at the same time. I've now got a portable induction hob on board too. 

They are controlled by BMV and a motorised switch, and the settings on the BtoB and Victron solar controller. 

I still have them in parallel with LAs and have a switch to select either paralleled or  charge by engine via BtoB

It could probably be more user friendly but I'd disconnect them if someone else was using the boat(heaven forbid). Engine charging could be vastly improved using an alternator controller as the BtoB gets at best 40a/hr out of the 175a alt..

I'm not a liveaboard and turn them off when leaving the boat.

I haven't plugged them into the software for ages as they we're always fine during the obsessive early days(months).

All in all I'm happy with how they are performing.

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3 hours ago, redwing said:

Thought I'd give an update on how my setup is performing after 2 years (tempting fate ?)

 

I have 3 2nd hand Valences, charged by 500w solar or 60amp Sterling BtoB.

On the whole they are performing well and I've often got more power than I know what to do with. Washing machine, immersion, kettle and toaster etc. use is limited by inverter capacity, but I'm careful not to use them at the same time. I've now got a portable induction hob on board too. 

They are controlled by BMV and a motorised switch, and the settings on the BtoB and Victron solar controller. 

I still have them in parallel with LAs and have a switch to select either paralleled or  charge by engine via BtoB

It could probably be more user friendly but I'd disconnect them if someone else was using the boat(heaven forbid). Engine charging could be vastly improved using an alternator controller as the BtoB gets at best 40a/hr out of the 175a alt..

I'm not a liveaboard and turn them off when leaving the boat.

I haven't plugged them into the software for ages as they we're always fine during the obsessive early days(months).

All in all I'm happy with how they are performing.

Very similar set up to mine (with the LAs in parallel). I think that is 4 years my system has done. Massive reduction in engine running to put power back in.

I've 2 * 60A Sterling BtoB's but given up with them as like you they only put out 40A heating the boat with the wasted 20A. I now just charge direct from the alternator and isolate when I get to 13.8v. No change whatsoever in battery performance since I got them (2nd hand ex vehicle).

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3 hours ago, redwing said:

Thought I'd give an update on how my setup is performing after 2 years (tempting fate ?)

 

I have 3 2nd hand Valences, charged by 500w solar or 60amp Sterling BtoB.

On the whole they are performing well and I've often got more power than I know what to do with. Washing machine, immersion, kettle and toaster etc. use is limited by inverter capacity, but I'm careful not to use them at the same time. I've now got a portable induction hob on board too. 

They are controlled by BMV and a motorised switch, and the settings on the BtoB and Victron solar controller. 

I still have them in parallel with LAs and have a switch to select either paralleled or  charge by engine via BtoB

It could probably be more user friendly but I'd disconnect them if someone else was using the boat(heaven forbid). Engine charging could be vastly improved using an alternator controller as the BtoB gets at best 40a/hr out of the 175a alt..

I'm not a liveaboard and turn them off when leaving the boat.

I haven't plugged them into the software for ages as they we're always fine during the obsessive early days(months).

All in all I'm happy with how they are performing.

 

15 minutes ago, Dr Bob said:

Very similar set up to mine (with the LAs in parallel). I think that is 4 years my system has done. Massive reduction in engine running to put power back in.

I've 2 * 60A Sterling BtoB's but given up with them as like you they only put out 40A heating the boat with the wasted 20A. I now just charge direct from the alternator and isolate when I get to 13.8v. No change whatsoever in battery performance since I got them (2nd hand ex vehicle).

My valence domestic are working fine, however disaster struck with my drive Valences, the lead from the solar controller somehow came lose? 3 years its been on there, anyway tightened up and all good again. The problem was though it looked like it was my Midnite controller that had gone duff so I wasted 2 days playing the wrong thing pure luck that I saw the lead spark, just shows high amps can cause poor contact over time 

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Our Lithiums have been in service since March this year. Only being charged by solar panels at the moment. Its far too early to say whether they have been a success, but so far, so good.

 

ETA.I couldn't have done it without a lot of help from people on this forum, so a huge thanks to you. You know who you are.

Edited by rusty69
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44 minutes ago, rusty69 said:

Our Lithiums have been in service since March this year. Only being charged by solar panels at the moment. Its far too early to say whether they have been a success, but so far, so good.

 

ETA.I couldn't have done it without a lot of help from people on this forum, so a huge thanks to you. You know who you are.

I rarely know who I am these days.

 

 

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46 minutes ago, rusty69 said:

Our Lithiums have been in service since March this year. Only being charged by solar panels at the moment. Its far too early to say whether they have been a success, but so far, so good.

 

ETA.I couldn't have done it without a lot of help from people on this forum, so a huge thanks to you. You know who you are.

We've been out nearly 3 months on our summer cruise this year. Now that Mrs Bob has added a 240v freezer to the bote inventory, we are usually above the 200Ahr power usage each 24 hours - but we have ice for the G&Ts. As routine as clockwork now, we find that if we are not moving, we need to run the engine for 1 hour a day (to heat the water) to put 80 odd Ahrs back in and the 500W of solar usually does the rest. I reckon we'd be running the engine at least 3 hours a day with LAs only. Our best day for solar was 216 Ahrs in (+/- the error in the BMV working out the power in - but that is another story) with no engine running. You would never have got anywhere near that with LAs.

I reckon these Li's will last 10 years+. I regularly look at resting voltage vs Ahrs out and  the results always fall on the same line (after resetting the BMV!). Spent a bit of time in the first 12 months balancing them.....but not touched them since. God, the're boring.

 

 

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2 minutes ago, Dr Bob said:

We've been out nearly 3 months on our summer cruise this year. Now that Mrs Bob has added a 240v freezer to the bote inventory, <snip>

 

 

You need to trade Mrs Bob in  for a less power hungry model. Mrs Rusty is only allowed the luxury of a freezer in the winter months.

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Mine are doing fine after that slight glitch with one of the terminal connections. Software for the BMS has been running continuously for over a year, not crashed yet. Which is just as well as I never got around to setting up the watchdog timer!
 

We are just setting off on a 4 week trip, but being mid summer there will be no chance of using a significant proportion of charge.

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20 minutes ago, nicknorman said:

 Software for the BMS has been running continuously for over a year, not crashed yet. Which is just as well as I never got around to setting up the watchdog timer!

How is your alternator controller performing? If I was starting again I might have asked you if you could've helped me make one, but to be honest it looked at bit beyond my capabilities at the time. I'm assuming it does the same job as the Mastervolt Alpha. 

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