Monitoring lithium batteries

[MtB]

3 minutes ago, peterboat said:

Mike buy 8 of those to sort out your battery problems for ever!!

 

You reckon they are LiFePO4 then? If so, why does the manu of the car they came from say they use something else? 

[TheBiscuits]

2 minutes ago, Mike the Boilerman said:

 

You reckon they are LiFePO4 then? If so, why does the manu of the car they came from say they use something else? 

Link please.  I only found vague reference to Fe batteries when I looked, which are either LFP or NiFe at a guess.

[peterboat]

Beijing has provided subsidies for electric buses using lithium-iron phosphate (LFP) batteries, a type used by BYD but not by many foreign manufacturers due to its lower power capacity.

Google is your friend Mike I would buy 8 of those batteries before someone else beats you to it

25 minutes ago, Mike the Boilerman said:

 

You reckon they are LiFePO4 then? If so, why does the manu of the car they came from say they use something else? 

Yes mike read my post

[nicknorman]

2 hours ago, Mike the Boilerman said:

 

The former I reckon. 

 

I have a switch to turn the field ON and if I forget to switch it ON, the alternator still loads up the engine and delivers full rated output once engine revs get up to about 250rpm. Annoying as the boat won't go very fast when it does this!

Yes so what that switch is doing is providing some initial stator current (typically via a warning bulb) to get things going, but once going it’s entirely self-stoking. And there is sufficient residual magnetism to get things going anyway, if the revs are high enough.

 

What you would need is a switch or relay to interrupt the current going between the field diodes and the stator, which would prevent any possibility of “self-stoking” and gracefully reduce the alternator output to near as dammit zero.

 

It would involve a little surgery to disconnect the wire going from the alternator regulator or field diodes to the stator, but no more than is required eg to install an ADVERC. Just a matter of removing the regulator to gain access to the wire.

 

All that said, I think an intelligent regulator that just reduces the charge voltage to a safe float value once the batteries are full is the much better option.

2 hours ago, Tom and Bex said:

I think this thread demonstrates the range of options available from the very basic with owner doing the monitoring and taking any action necessary, to the complex fully integrated (expensive!) systems from the likes of Victron and Mastervolt etc. I suspect most real life systems fall somewhere between these 2 extremes (as does ours).

 

Our 2nd hand cells came from http://www.ev-support.co.uk and we paid £600 for 8 Thundersky 160ah cells. Those ones MTB linked to above look like good value if they are as they say they are. 

 

If anyone interested is in the Lapworth area, I'd be happy to show them our system and talk it through with them. 

Can you give me an idea how much the Arduino regulator cost and did you have to solder it up yourself?

[MtB]

34 minutes ago, TheBiscuits said:

Link please.  I only found vague reference to Fe batteries when I looked, which are either LFP or NiFe at a guess.

 

Ok I'm back home now so can post links. 

 

A couple of weeks go when I first looked I found a section on the BYD site promoting an ordinary car but today I can't find it. Nearest thing is a taxi, which also says it uses "BYD Iron Phosphate (Fe) Battery", which I think the other page might have said too.

 

Not sure there ARE any other battery technologies that could have been used anyway...

[TheBiscuits]

And a bit more digging suggests byd are the largest manufacturer of LFP batteries ... so I suspect they are!

 

While rummaging, I also found the EMUS BMS modular system which looks very interesting:

 

https://emusbms.com/wp-content/uploads/2018/04/Emus_BMS_User_Manual_v.1.2.1.pdf

 

https://www.nothnagel-marine.de/index.php?cat=c266_EMUS-BMS-System.html&filter_id=37&language=en

 

[Tom and Bex]

24 minutes ago, nicknorman said:

Can you give me an idea how much the Arduino regulator cost and did you have to solder it up yourself?

I got mine from here http://arduinoalternatorregulator.blogspot.com/?m=0 and think it cost about $120. Came fully assembled, but as just a board so mounted it in a cheap box from Toolstation. Found the chap extremely helpful when emailing him with questions, I had zero experience of arduino and programming prior to this, but with his help was able to set it up and change some of the parameters to suit my needs. Says currently out of stock but always worth an email. He wasn't pushing me for a sale at any point, just very helpful with my enquiries. 

 

1 hour ago, peterboat said:

Mike buy 8 of those to sort out your battery problems for ever!!

Not sure if it's the same seller, but I did look at these when I was looking, but unfortunately they had sold out. 

[Tom and Bex]

28 minutes ago, TheBiscuits said:

While rummaging, I also found the EMUS BMS modular system which looks very interesting:

Can't remember seeing that one before. I was looking at the smart 123 BMS from here https://www.ev-power.eu/Battery-Management/123-Smart-BMS-Complete-Set-4-cells-with-Bluetooth-4-0.html but went with a simpler and cheaper option in the end. 

[eid]

On 29/11/2018 at 10:25, Robbo said:

Cell>4V or temperature (red): charge disconnect output low because of imminent cell over voltage or over temperature. -

Cell>2,8V (blue): load disconnect output high. Load disconnect output low when off, due to imminent cell under voltage (Vcell≤2,8V).

 

I noticed yesterday in the Victron Connect app, there is the feature to reduce the cell under-voltage down to 2.6V. Now if they would add the feature to reduce cell over-voltage, the need to do cut off the charge in other ways would be negated.

I notice however that you don't seem to think this is necessary. I wonder, do you have a Victron system installed, relying on the BMS to cut off the alternator?

 

 

 

 

 

 

[eid]

On 28/11/2018 at 16:03, Mike the Boilerman said:

 

I gave two examples actually

 

In the case of over-voltage you could just look at the volt meter and make a judgement about how much over the voltage is, and balance this with with how much longer you need to cruise before stopping. If you see fit, you could just moor up and stop the engine immediately.

 

If cell imbalance is indicated you would just make a note of it, then next weekend disconnect your bank and use a bench power supply to accurately charge each cell individually to precisely the same voltage, put the bank back together again and carry on for a few more years before it needs doing again. 

 

 

 

 

 

I've been thinking about this a lot since yesterday. It would certainly be a lot cheaper than the system I had quoted.

 

I think stopping cruising might work on short journeys, as the batteries charge so quickly and I don't really use much electricity anyway. On longer journeys I'd have to cut the alternator manually I guess. I could use my Victron battery monitor's alarm to tell me when the voltage reaches the desired figure, though it is not very loud so I may have to use it's relay in conjunction with one of these bolted to the roof:

 

https://www.youtube.com/watch?v=DD0Ry32NP5c&feature=youtu.be&t=12

 

 

 

What would rebalancing manually entail; opening the battery and disconnecting each cell before measuring voltage?

 

 

The only other difficulty would be getting batteries that have decent amount of cycles left on them. Is there a way to tell?

 

Edited November 30, 2018 by eid

[Tom and Bex]

3 hours ago, eid said:

I noticed yesterday in the Victron Connect app, there is the feature to reduce the cell under-voltage down to 2.6V. Now if they would add the feature to reduce cell over-voltage, the need to do cut off the charge in other ways would be negated.

As Nick says, ideally the system should be designed so the cell under and over voltage protection never activates and is there as a fail safe only. If the under or over voltage cuts in there had already been a failure of some sort, so the protection cuts in to save the expensive batteries from destruction. 

 

3 hours ago, eid said:

I've been thinking about this a lot since yesterday. It would certainly be a lot cheaper than the system I had quoted.

It would be cheaper, but would rely entirely on manual intervention to protect potentially very expensive batteries. Depends how much risk you are prepared to take. Having said that, these batteries are more robust than many think though. 

 

3 hours ago, eid said:

I could use my Victron battery monitor's alarm to tell me when the voltage reaches the desired figure, though it is not very loud

That's why we use the ISDT BC-8S to monitor cell voltages and have set the alarms to alert me prior to the BMS high and low voltage levels. This has quite a loud alarm (90db?) considering the size and price, certainly loud enough to hear above the engine whilst cruising, and at the opposite end of the boat. 

 

3 hours ago, eid said:

What would rebalancing manually entail; opening the battery and disconnecting each cell before measuring voltage?

Initial (top) balancing should be done by connecting all cells in parallel, and charging at 3.8v until current drops to pre determined level. You can do manual rebalancing whilst cells are connected, by noting which cell(s) are slightly high/low at end of charge, and applying a load across high cells to bring them more in line (or charge low cells). This can involve a bit of guesswork though, and parallel balancing is the preferred method. Having said that, experience shows rebalancing should rarely be necessary.

 

3 hours ago, eid said:

The only other difficulty would be getting batteries that have decent amount of cycles left on them. Is there a way to tell?

Unfortunately, unless you use the valence ones such as peterboat where you can connect up computer to see number of cycles and other usage data, you have to rely on the trustworthiness of the seller. About the only other checks that are easy to do, are check for any bulging of cells, and check voltage level. 

Edited November 30, 2018 by Tom and Bex
Change balance voltage from 13.8 to 3.8!

[MtB]

9 hours ago, Tom and Bex said:

Initial (top) balancing should be done by connecting all cells in parallel, and charging at 3.8v until current drops to pre determined level. You can do manual rebalancing whilst cells are connected, by noting which cell(s) are slightly high/low at end of charge, and applying a load across high cells to bring them more in line (or charge low cells). This can involve a bit of guesswork though, and parallel balancing is the preferred method. Having said that, experience shows rebalancing should rarely be necessary.

 

 

And designing some electronics to do this automatically without user intervention, and without taking the batteries off line, is quite some feat as you can imagine. This is one of the reasons proprietary systems like Victron are I suspect, so expensive. 

[MoominPapa]

9 hours ago, Mike the Boilerman said:

 

And designing some electronics to do this automatically without user intervention, and without taking the batteries off line, is quite some feat as you can imagine. This is one of the reasons proprietary systems like Victron are I suspect, so expensive. 

Actually, it's not too bad. (Says he, who knows the theory, but is still working on the practise!) 

 

There chips available that include analog-to-digital converters to read the cell voltages, and transistors and drive circuits to sink some current through a resistor across the battery. All you need to provide is an algorithm that uses the cell-voltage readings to decide which cells need to waste a bit of current, and then set the bits in the cell-balance register corresponding to those cells. The ends of the series string and each cell-cell connection are connected to pins on the chip via low value resistors that actually dissipate the power.

 

The main problem I'm having with this at the moment is that the chips are only available in surface-mount packages with pins on 0.6mm centres. Those are a serious challenge to hand-solder, and really don't work on veroboard.

 

MP.

 

ETA, The point of the post, if it's not obvious, is that once you've arranged to be able to read cell voltages, balancing ability comes more-or-less for free.

Edited December 1, 2018 by MoominPapa

[peterboat]

On 30/11/2018 at 15:04, Tom and Bex said:

As Nick says, ideally the system should be designed so the cell under and over voltage protection never activates and is there as a fail safe only. If the under or over voltage cuts in there had already been a failure of some sort, so the protection cuts in to save the expensive batteries from destruction. 

 

It would be cheaper, but would rely entirely on manual intervention to protect potentially very expensive batteries. Depends how much risk you are prepared to take. Having said that, these batteries are more robust than many think though. 

 

That's why we use the ISDT BC-8S to monitor cell voltages and have set the alarms to alert me prior to the BMS high and low voltage levels. This has quite a loud alarm (90db?) considering the size and price, certainly loud enough to hear above the engine whilst cruising, and at the opposite end of the boat. 

 

Initial (top) balancing should be done by connecting all cells in parallel, and charging at 3.8v until current drops to pre determined level. You can do manual rebalancing whilst cells are connected, by noting which cell(s) are slightly high/low at end of charge, and applying a load across high cells to bring them more in line (or charge low cells). This can involve a bit of guesswork though, and parallel balancing is the preferred method. Having said that, experience shows rebalancing should rarely be necessary.

 

Unfortunately, unless you use the valence ones such as peterboat where you can connect up computer to see number of cycles and other usage data, you have to rely on the trustworthiness of the seller. About the only other checks that are easy to do, are check for any bulging of cells, and check voltage level. 

I did the all batteries in parallel after I had charged them all individually, when I put the puter on the cells and batteries were all in balance. I check the batteries very occasionally now and its always the same cells and batteries in balance, James who I bought the batteries from is the same. I think that the restricted charging regime is the reason for this, and in practice it doesnt matter 13.8 volts down to 11 is more than enough

[MtB]

8 hours ago, MoominPapa said:

Actually, it's not too bad. (Says he, who knows the theory, but is still working on the practise!) 

 

There chips available that include analog-to-digital converters to read the cell voltages, and transistors and drive circuits to sink some current through a resistor across the battery. All you need to provide is an algorithm that uses the cell-voltage readings to decide which cells need to waste a bit of current, and then set the bits in the cell-balance register corresponding to those cells. The ends of the series string and each cell-cell connection are connected to pins on the chip via low value resistors that actually dissipate the power.

 

The main problem I'm having with this at the moment is that the chips are only available in surface-mount packages with pins on 0.6mm centres. Those are a serious challenge to hand-solder, and really don't work on veroboard.

 

MP.

 

ETA, The point of the post, if it's not obvious, is that once you've arranged to be able to read cell voltages, balancing ability comes more-or-less for free.

 

This is all WAY above my level of competence, which is about at the level of the Ladybird book "Magents, Bulbs and Batteries".

https://www.amazon.co.uk/Magnets-Batteries-Ladybird-December-Hardcover/dp/B015YLTW1W?SubscriptionId=AKIAILSHYYTFIVPWUY6Q&tag=duc08-21&linkCode=xm2&camp=2025&creative=165953&creativeASIN=B015YLTW1W

 

(£89? ffs!!)

 

Ebay however decided to send me a link to a cheapo BMS sold in the UK that gets us possibly half way there...

 

https://www.ebay.co.uk/itm/173668095709?ul_noapp=true

 

 

 

[nicknorman]

9 hours ago, MoominPapa said:

 

The main problem I'm having with this at the moment is that the chips are only available in surface-mount packages with pins on 0.6mm centres. Those are a serious challenge to hand-solder, and really don't work on veroboard.

 

MP.

 

Actually I quite like working with SM devices, but you do have to take a different approach. Bin the soldering iron, get a hot air rework station (£35 or so from eBay) which is dead useful for other stuff too. And some solder paste. You just put a tiny dab of solder paste on the pads and roast up with the hot air.

 

i am reasonably good at making single sided SM boards but with the small sizes you allude to, it gets difficult to make double sided and then there are the vias to worry about. However I have recently discovered a Chinese company called Elecrow who will make a batch of say 10 smallish double sided PCBs with solder mask and silkscreen for 5 USD. Incredibly cheap! Of course if you want them in a hurry you have to pay for DHL which is 25USD but otherwise if you can wait for ordinary Chinese postage it’s very cheap. To be honest I haven’t tried them yet but they seem to have a good reputation.

 

currently working of a project with these tiny pressure sensors, underneath are 8 pads to be soldered. No chance of using a soldering iron.

 

PIC microcontrollers are fully loaded with endless analogue and digital peripherals, can be programmed in C and cost just over a quid!

 

Oh and I use RS’ Design Spark free schematic and PCB design software.

Edited December 1, 2018 by nicknorman

[Johny London]

I found this thing but no idea if it would be useful...

https://www.ebay.co.uk/itm/Digital-Battery-Capacity-Checker-Cell-Meter-For-LiPo-LiFe-Li-ion-RC-Models/291495287560

[MtB]

On 06/12/2018 at 11:14, Johny London said:

I found this thing but no idea if it would be useful...

https://www.ebay.co.uk/itm/Digital-Battery-Capacity-Checker-Cell-Meter-For-LiPo-LiFe-Li-ion-RC-Models/291495287560

 

I'm not sure it is that useful as it has no output to operate a relay or audio alarm.

 

While I'm on I bought 8 x 200ah lithium batts today for £640, out of that vandalised BYD car. The chap has plenty more if anyone is interested. 

 

I didn't initially realise but ALL the batteries he is selling are out of the same wrecked car. The wrecked car is there to inspect if anyone wishes. He is a clever bloke, and is currently converting a really nice Landy to electric-only power. Several other cars there on site beautifully converted. 

[peterboat]

16 hours ago, Mike the Boilerman said:

 

I'm not sure it is that useful as it has no output to operate a relay or audio alarm.

 

While I'm on I bought 8 x 200ah lithium batts today for £640, out of that vandalised BYD car. The chap has plenty more if anyone is interested. 

 

I didn't initially realise but ALL the batteries he is selling are out of the same wrecked car. The wrecked car is there to inspect if anyone wishes. He is a clever bloke, and is currently converting a really nice Landy to electric-only power. Several other cars there on site beautifully converted. 

Good buy Mike glad you listened just remember the mantra.................never more than 80% or less than 20% and they will outlive me.

If you feel that way inclined a BMS to do 8 cells shouldnt be expensive have a look on the DIY electric car forum they have a section for it, and they know what they are doing or at least some of them do ?

[MtB]

4 hours ago, peterboat said:

Good buy Mike glad you listened just remember the mantra.................never more than 80% or less than 20% and they will outlive me.

If you feel that way inclined a BMS to do 8 cells shouldnt be expensive have a look on the DIY electric car forum they have a section for it, and they know what they are doing or at least some of them do ?

 

Fanx.

 

So now I need to get to know them. First thing to do is assess the state of charge and acquire some sort of monitoring. I'm inclined to go the 'alarm' route rather than have the unnecessary complexity of positive cut-offs using relays. Low voltage, high voltage, cell imbalance, over temp, under temp. None is critical to shut down IMMEDIATELY. If I know there is a problem I can spend five or ten minutes considering what to do about it.

 

I'll have a look at the DIY electric car forum, thanks fore the tip. 

 

 

 

[WotEver]

Just got an email from TI and when nosing around their site I found this:

http://www.ti.com/solution/battery_management_high_cell_count_for_hev?variantid=14006&subsystemid=17171

 

Might interest some of you. 

[MtB]

On 08/12/2018 at 01:50, Mike the Boilerman said:

 

I'm not sure it is that useful as it has no output to operate a relay or audio alarm.

 

While I'm on I bought 8 x 200ah lithium batts today for £640, out of that vandalised BYD car. The chap has plenty more if anyone is interested. 

 

I didn't initially realise but ALL the batteries he is selling are out of the same wrecked car. The wrecked car is there to inspect if anyone wishes. He is a clever bloke, and is currently converting a really nice Landy to electric-only power. Several other cars there on site beautifully converted. 

 

And here's the link. Chappie has plenty more although they are in packs configured to different voltages. I bought an 8 cell pack at 26v nominal. 

 

https://www.ebay.co.uk/itm/LiFePo4-26v-200Ah-Battery-Home-Storage-For-Solar-Energy-Ev-Project/273595680407?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

 

 

 

 

Edited December 12, 2018 by Mike the Boilerman
Multiple post bug strikes again

[MtB]

And here is what’s under the lid of my box. 

 

Rather weird once you look properly...

 

 

[Johny London]

Regarding the original question - monitoring, I see this meter now comes with the option of 500a shunt: https://www.ebay.co.uk/itm/New-DC-0-120V-0-200A-Volt-Amp-Capacity-Power-Watt-Meter-Battery-State-of-Charge/181289964449?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20131017132637%26meid%3Db9e084c7426c4a84b4621a9dd7321e25%26pid%3D100033%26rk%3D5%26rkt%3D8%26mehot%3Dag%26sd%3D113419653552%26itm%3D181289964449&_trksid=p2045573.c100033.m2042

I remember looking sometime ago when someone on here got one, but at the time I don't think it could do that much amps.

Wonder if these are good for lithiums because they can apparently count amps in and out - like a Victron meter only a fraction of the price? Perhaps the person who has one of these can advise?

[WotEver]

5 minutes ago, Johny London said:

Wonder if these are good for lithiums because they can apparently count amps in and out...

If you want to count Ah then yes, they do this. If you want a safe lithium system with high and low charging protection, cell balancing, auto shut-off etc then they do nothing towards that.