Cheap LiFePO4 BMS?

[Murflynn]

21 hours ago, Dr Bob said:

If you understand Volts, Amps,  Amphours used and have kit to measure that lot and know how to use it on Lead Acids, then Lithiums are pretty simple.

The discussion on here spends an awful lot of time on things like balancing which I only do once per year and its pretty easy once you understand the rules for Lithiums. As long as you set up with safeguards over excessive charging etc then Li's become very simple. Dont let all this hi tech stuff put you off. You dont need to create computer based battery management systems and just buy off the shelf components and bolt them together.

You'll never again need to worry about having to charge to 100%.

It really is very easy for someone with a reasonable level of battery management knowledge.

thanks Bob.  that cuts through all the carp and gives me a better sense of direction.   I reckon the only precautions I have to take in practice are:

1.  purchase a purpose made Lipo charger because my "7 stage" charger will keep trying to equalise and other smart things including occasionally shocking the L/As with 16.5v.*

2.  configure my MPPT solar controller to suit the Lipos.

3.  remove or keep the Lipos warm in winter.

 

* I'm supposing that a charger like this one will not allow overcharging:

   https://www.ebay.co.uk/itm/20A-12v-LiFePo4-Lithium-iron-phosphate-Battery-Charger/293653013541?hash=item445f156425:g:0ysAAOSwoGpfCwMN

 

 

[WotEver]

4 minutes ago, Murflynn said:

I'm supposing that a charger like this one will not allow overcharging:

Presumably, but the info on the ad is somewhat sparse and the link to the instructions has been removed.  You could give them a call to discuss it I guess?

[MoominPapa]

24 minutes ago, Murflynn said:

 

 

* I'm supposing that a charger like this one will not allow overcharging:

   https://www.ebay.co.uk/itm/20A-12v-LiFePo4-Lithium-iron-phosphate-Battery-Charger/293653013541?hash=item445f156425:g:0ysAAOSwoGpfCwMN

 

 

I can't see how, If it just limits the voltage to the 14.6v in the spec it sure as hell will overcharge them. As discussed here in the past., any charger that bases charge limit simply on regulating the voltage, will either overcharge or have a voltage limit so low that it takes days to actually charge the batteries. To do charge termination, the charger needs to have some method of determining the SoC, and that needs it to be able to measure the battery current (not the charger current.)

 

MP.

 

 

[Dr Bob]

3 hours ago, MoominPapa said:

I can't see how, If it just limits the voltage to the 14.6v in the spec it sure as hell will overcharge them. As discussed here in the past., any charger that bases charge limit simply on regulating the voltage, will either overcharge or have a voltage limit so low that it takes days to actually charge the batteries. To do charge termination, the charger needs to have some method of determining the SoC, and that needs it to be able to measure the battery current (not the charger current.)

 

MP.

 

 

 

4 hours ago, Murflynn said:

 

* I'm supposing that a charger like this one will not allow overcharging:

   https://www.ebay.co.uk/itm/20A-12v-LiFePo4-Lithium-iron-phosphate-Battery-Charger/293653013541?hash=item445f156425:g:0ysAAOSwoGpfCwMN

 

 

MP is of course right in talking about termination of charge based on voltage and current but it can be done based just on voltage (which is exactly what I do) if you go for lower voltages.

ALL (and I mean ALL) of the Lifepo4 chargers I have seen go for much higher voltages which will overcharge. My victron charger on my old boat with a LiFePo4 setting was crap. My Sterling BtoB's are crap on the Lifepo4 setting.

The best way to have an auto disconnect is to use a victon BMV battery monitor and use the voltage measured to terminate charge between 13.8V and 14.0V and activate an isolation relay. Those voltages are fine to terminate charge at 80-90% which is all you need. If you want to go to 90-100% then you need to listen to MP and use tail current to disconnect but why? 80-90% charge is enough. Never go near 100% SoC and avoid balancing issues. If you do want to go to 100%, then you can do that manually and watch the charge rise and turn it off when you get there..

It is best of course to have charge sources that back off before your autodisconnect activates and there is plenty of info in this thread to work out how to do that. We can advise on the best way to get them to back off but we need to know your specific set up.  Solar is easy to get it  to go to float. Alternators a little more tricky. Combi's are even trickier.

Edited September 6, 2020 by Dr Bob

[nicknorman]

5 hours ago, MoominPapa said:

No, The pattern in remarkably consistent. There's one cell that always has the most charge removed, another which has somewhat less, and the the other too take the place of the lowest cell more-or-less at random.

 

MP.

 

Thanks. Because we cruise a lot and/or are on shore power, and have precise control over charging voltages from alternator and Combi, I was thinking of an algorithm that would adjust the charge voltage such that the highest cell was say 3.65v, activate the balancing resistors on the higher cells until they were all at 3.65, then stop charging when the current fell to the relevant % of capacity to get 100% SoC. But perhaps you way is better because it avoid holding a cell at 3.65v for possibly several hours.

[WotEver]

3 hours ago, MoominPapa said:

I can't see how, If it just limits the voltage to the 14.6v in the spec it sure as hell will overcharge them

I wondered what “two step automatic charge process with Led charge indicator” meant? I guessed it meant ‘drops down to float’ but maybe not. So what’s the microprocessor control do, I wonder. 

[MoominPapa]

37 minutes ago, nicknorman said:

Thanks. Because we cruise a lot and/or are on shore power, and have precise control over charging voltages from alternator and Combi, I was thinking of an algorithm that would adjust the charge voltage such that the highest cell was say 3.65v, activate the balancing resistors on the higher cells until they were all at 3.65, then stop charging when the current fell to the relevant % of capacity to get 100% SoC. But perhaps you way is better because it avoid holding a cell at 3.65v for possibly several hours.

To make that work may require  large currents in the balance resistors and consequent large dissipation. My way can use very small balancing currents and just spreads the balancing out over up to twelve hours, in the extreme case. (The balance current is ~200mA,  so the maximum charge removal of 2.5Ah takes 12.5 hours)

 

MP.

 

[nicknorman]

2 hours ago, MoominPapa said:

To make that work may require  large currents in the balance resistors and consequent large dissipation. My way can use very small balancing currents and just spreads the balancing out over up to twelve hours, in the extreme case. (The balance current is ~200mA,  so the maximum charge removal of 2.5Ah takes 12.5 hours)

MP.

Ok I can see that, but 0.2A seems a very low current. I was thinking of using 50w resistors so current could be 5A or more, without them getting too hot. The AD7280 chip I’m using can only programme the balance output to be active for a max time of 37 minutes. Of course I can always retrigger them from the micro, but life (coding) would be a bit easier if I could send the requisite time to the hardware balance output timers and then forget! (ie get it done in 37 mins). At the expense of chunkier resistors and FETs of course.

[Murflynn]

It seems odd that even though there are millions of mobility buggies and golf carts out there, most being equipped with Lifepo4 batteries, no-one can identify or recommend a suitable charger.

[nicknorman]

1 hour ago, Murflynn said:

It seems odd that even though there are millions of mobility buggies and golf carts out there, most being equipped with Lifepo4 batteries, no-one can identify or recommend a suitable charger.

There are some to be found on eBay. I have personal experience of this one, we use it on our glider batteries. But of course they are only 7.5Ah and the charger is only 4A - which is plenty for an overnight charge for a mobility buggy. When the battery reaches fully charged, it shuts off.

 

https://www.ebay.co.uk/itm/MOTOCADDY-GOLF-BATTERY-LiFePo4-CHARGER-4-AMP-BLUE-BLACK-CONNECTOR-12-8V-4S/264781628755?hash=item3da6370553:g:eG0AAOSwkXBdjL2r
 

no personal experience of this one  but it seems to operate likewise (shuts off when fully charged), and 30A

 

https://www.ebay.co.uk/itm/12V-30A-LITHIUM-BATTERY-LIFEPO4-240V-CHARGER/293694590974?hash=item44618fcffe:g:GpIAAOSwODZfIySD

 

I should add that these chargers are designed to charge batteries with built in BMS, not bare cells.

Edited September 7, 2020 by nicknorman

[Dr Bob]

55 minutes ago, Murflynn said:

It seems odd that even though there are millions of mobility buggies and golf carts out there, most being equipped with Lifepo4 batteries, no-one can identify or recommend a suitable charger.

I may get shot down here by the experts who know charging but one of the issues is how fast you charge. As Li's accept a big charge through most of their charge cycle (unlike LAs), everyone wants to charge fast. On my 480Ahr bank, the MPPT solar controls worked fine and went to float at the right time but that was charging at 10-30A with a max charge of 30A At that charge you are always in bulk (constant current) so the termination point is easy based on voltage. My Sterling AtoB also terminated well as that had a limit of 40A so never got to the constant voltage phase.

On our new set up, I am charging at 90-100A which means I do get to the constant voltage phase if I go too far i.e. over 90%. I guess most chargers want to get you up to at least 95% so therein lies the problem.

I wouldn't trust any charger that 'picks' it's own termination point but it's not difficult to find your own solution. 

For me though, the charger is the least of the problem as I hardly ever use mine as we never charge the Li's on return to the marina...as they are then isolated ....and then I just charge for a set number of hours before leaving the marina but with the autodisconnect in place if necessary. We don't use a genny but if I did I would just put it on a timer. More important to plan your system on the solar and alternator.

[peterboat]

4 minutes ago, Dr Bob said:

I may get shot down here by the experts who know charging but one of the issues is how fast you charge. As Li's accept a big charge through most of their charge cycle (unlike LAs), everyone wants to charge fast. On my 480Ahr bank, the MPPT solar controls worked fine and went to float at the right time but that was charging at 10-30A with a max charge of 30A At that charge you are always in bulk (constant current) so the termination point is easy based on voltage. My Sterling AtoB also terminated well as that had a limit of 40A so never got to the constant voltage phase.

On our new set up, I am charging at 90-100A which means I do get to the constant voltage phase if I go too far i.e. over 90%. I guess most chargers want to get you up to at least 95% so therein lies the problem.

I wouldn't trust any charger that 'picks' it's own termination point but it's not difficult to find your own solution. 

For me though, the charger is the least of the problem as I hardly ever use mine as we never charge the Li's on return to the marina...as they are then isolated ....and then I just charge for a set number of hours before leaving the marina but with the autodisconnect in place if necessary. We don't use a genny but if I did I would just put it on a timer. More important to plan your system on the solar and alternator.

He only has solar and a mains charger as like me he is full electric, he needs a proper charger for when the sun doesn't shine 

[MoominPapa]

8 hours ago, nicknorman said:

Ok I can see that, but 0.2A seems a very low current. I was thinking of using 50w resistors so current could be 5A or more, without them getting too hot.

At less than a watt dissipation, there's no problem with heat-sinking or getting rid of the heat. The actual value was almost an accident, chosen early in the design when I had very little idea,  but it's turned out to be fine. No reason I can see not to use larger balance currents, as long as you arrange from the electronics to not fry.

 

MP.

 

6 minutes ago, Dr Bob said:

We don't use a genny but if I did I would just put it on a timer. More important to plan your system on the solar and alternator.

Charging with the genny is the one time I really want to get to 100% and ASAP. If I'm using the genny that implies we're not moving much, so not much charge will be available from the engine in the near future, and I want to amortise the cost of getting the genny out, filling it with petrol, connecting it up and pulling the cord over as many angry pixies as possible.

 

MP.

[Richard10002]

5 hours ago, Murflynn said:

It seems odd that even though there are millions of mobility buggies and golf carts out there, most being equipped with Lifepo4 batteries, no-one can identify or recommend a suitable charger.

The fact is that the settings for Lifepo4 can vary from user to user, and system to system, so there isnt one suitable setting, nor one suitable charger.

 

I use a Sterling Pro Charge Ultra 60A charger. It has a custom setting for Max Voltage and float voltage - you can set it as high or as low as you like, (within limits). I set them both the same, at 14.8V, and that serves my Li Bank fine, given a bit of voltage drop. I would set them both much lower if I was on shore power, rather than genny.

[Murflynn]

5 hours ago, nicknorman said:

 

https://www.ebay.co.uk/itm/12V-30A-LITHIUM-BATTERY-LIFEPO4-240V-CHARGER/293694590974?hash=item44618fcffe:g:GpIAAOSwODZfIySD

 

I should add that these chargers are designed to charge batteries with built in BMS, not bare cells.

that's the same as the one I posted, charges to 14.6v, already commented on by Moomin Papa.

 

Valence batteries that I am interested in apparently have some form of internal BMS and protection, but I am not about to invest £1000 in a new battery bank when such anomalies cannot be clarified.

 

the industry does not make is easy and the wise words from experts on this forum and on specialist websites just fill me with a sense of impending doom!!

 

I am a qualified engineer (civil) and understand basic electrical engineering, but once monitoring by laptop and balancing cells is mentioned my mind goes into blank mode.

[Richard10002]

5 minutes ago, Murflynn said:

Valence batteries that I am interested in apparently have some form of internal BMS and protection, but I am not about to invest £1000 in a new battery bank when such anomalies cannot be clarified.

 

the industry does not make is easy and the wise words from experts on this forum and on specialist websites just fill me with a sense of impending doom!!

I have the Valence batteries:

 

1) the internal electronics provide no protection, but do allow monitoring, once you have worked out the cabling to connect them to a laptop - if I can do it, most people can

 

2) You could do what Peter does, and set them to charge to a max of 13.9V, plus not let them go below about 12.5V, and Bob seems to be your Uncle.

 

3) on temperature, you can use them with gay abandon at any temperature, you merely shouldn't charge them below about 5C. How low does your boat get?

 

In order to protect your LA bank, you have to follow some rules - it's the same with Li, merely different rules.

[Murflynn]

3 hours ago, Richard10002 said:

I have the Valence batteries:

 

1) the internal electronics provide no protection, but do allow monitoring, once you have worked out the cabling to connect them to a laptop - if I can do it, most people can

 

2) You could do what Peter does, and set them to charge to a max of 13.9V, plus not let them go below about 12.5V, and Bob seems to be your Uncle.

 

3) on temperature, you can use them with gay abandon at any temperature, you merely shouldn't charge them below about 5C. How low does your boat get?

 

In order to protect your LA bank, you have to follow some rules - it's the same with Li, merely different rules.

how?  is there a mains charger (20A or thereabouts) that can be set to that figure without complex (for me) electronicky?

[Richard10002]

10 minutes ago, Murflynn said:

how?  is there a mains charger (20A or thereabouts) that can be set to that figure without complex (for me) electronicky?

Sterling Pro Charge Ultra. The lowest might be 30A. You can also set them to charge at 75%, 50%, and 25%, of the max.

 

Its a bit of a button pressing faff to set up the Custom settings but, as I said, if I can do it, you can do it.

[Dr Bob]

1 hour ago, Murflynn said:

how?  is there a mains charger (20A or thereabouts) that can be set to that figure without complex (for me) electronicky?

...or if you keep one or two of your LA's, you could use the Sterling BtoB with its own custom setting and using your existing charger to charge the LAs.

However, if you are spending £1000 on Li cells then it would be prudent to set up your own BMS which disconnects the Li's on over charge, undercharge and low temp - ie the simpest is via a BMV battery monitor connected to a Sterling BtoB which shuts down when told to by the BMV but maybe you want a separate shut down system with the BMV connected to another relay. Relying on just a charger to shut down is a risk so having your own independent disconnect is a good idea.

[magnetman]

New to this topic but I am planning to make a portable Lithium power bank. It's going to be a Peli 1400 case with 8 pcs Calb LiFePo4 cells each one 20ah. So that will result in a 4s 2p block which will be 40ah at 12v nominal. 

 

They fit in the Peli case perfectly with a little bit of space for ventilation and an MPPT controller plus maybe a BMS. 

 

I reckon the way to charge these from mains is with a hobby RC plane charger.  https://www.hobbyrc.co.uk/skyrc-t200-200w-acdc-charger these have all different settings and charge up to 12a. Ok not that fast but suitable. And they have balance charging option. 

 

I was planning to shoe horn a Victron MPPT into the box as well so that the Low Voltage Disconnect can be used to remove load from the batteries to avoid full discharge, via a relay or solenoid. 

 

The reason for wanting this battery is I spend half the time on one boat and half the time on another one and I sometimes have mains access so a portable unit charged by more or less anything seems sensible. 

 

And I am a very low power user. 

 

And it can be used as a jump starter pack if I put in large wires and an Anderson connector. 

 

Sound ok ?

 

Edited September 9, 2020 by magnetman

[Dr Bob]

40Ahr seems very small for a narrow boat. If you are a very small user then aren't the boat batteries big enough? Maybe good for a small grp cruiser without an alternator.

[magnetman]

55 minutes ago, Dr Bob said:

40Ahr seems very small for a narrow boat. If you are a very small user then aren't the boat batteries big enough? Maybe good for a small grp cruiser without an alternator.

I've got more than one boat. All of them are fairly large and comfortable  residential vessels but I use very little power on off grid boats. No fridge, no telly no computer just lights, pumps and phone charging basically. Engines never run unless moving because I disagree with doing that unless absolutely necessary, which it absolutely isn't in most situations . Solar not much use in winter. I have had more generators than you could shake a stick at I don't want a generator any more. 

 

Don't forget a 40ah LFP battery is about the same as 80ah SLA due to the amount of power you can sensibly use. 

 

It just seems a useful way to package mains electric and carry it around. 

It's easily enough for me for a few days on any of the boats. They have their own electric systems already fitted that's not a problem but I don't run the engine when not moving... And sometimes in winter moving is not practical (Thames ).

 

I know some people like fabulous luxuries but one of the joys of boats for me is that you can get away from all the excess and just do things in a basic way.  

 

Phones are good for media because they are such low consumption. Mine is charging now and drawing just 0.33amps from 12v. Talk about efficiency!

Edited September 9, 2020 by magnetman

[Murflynn]

On 07/09/2020 at 18:24, Dr Bob said:

...or if you keep one or two of your LA's, you could use the Sterling BtoB with its own custom setting and using your existing charger to charge the LAs.

However, if you are spending £1000 on Li cells then it would be prudent to set up your own BMS which disconnects the Li's on over charge, undercharge and low temp - ie the simpest is via a BMV battery monitor connected to a Sterling BtoB which shuts down when told to by the BMV but maybe you want a separate shut down system with the BMV connected to another relay. Relying on just a charger to shut down is a risk so having your own independent disconnect is a good idea.

.................   and there we go - a solution that is probably fraught with pitfalls for the unwary. 

 

the only solution that seems to fit my philosophy is a Sterling Pro-charge Ultra.   thank you Richard.

[Dr Bob]

17 minutes ago, magnetman said:

I've got more than one boat. All of them are fairly large and comfortable  residential vessels but I use very little power on off grid boats. No fridge, no telly no computer just lights, pumps and phone charging basically. Engines never run unless moving because I disagree with doing that unless absolutely necessary, which it absolutely isn't in most situations . Solar not much use in winter. I have had more generators than you could shake a stick at I don't want a generator any more. 

 

Don't forget a 40ah LFP battery is about the same as 80ah SLA due to the amount of power you can sensibly use. 

 

It just seems a useful way to package mains electric and carry it around. 

It's easily enough for me for a few days on any of the boats. They have their own electric systems already fitted that's not a problem but I don't run the engine when not moving... And sometimes in winter moving is not practical (Thames ).

 

I know some people like fabulous luxuries but one of the joys of boats for me is that you can get away from all the excess and just do things in a basic way.  

 

Phones are good for media because they are such low consumption. Mine is charging now and drawing just 0.33amps from 12v. Talk about efficiency!

I am sure what you are saying will work, but it to me there must be an easier way to do it.

You say you spend half your time on one boat and half on the other but only sometimes have access to mains power to recharge the Li pack. What happens when you cant charge it? It sounds like you have solar so for 8-9 months of the year, you should be fine with the solar keeping your LAs full if you are such a low power user. Ok the other 3-4 months of the year you need to find another source of power.

You say you only run your engine when moving....but how do you heat your water? When off grid we run our engine for an hour a day which heats the water and charges the Li's.

You say your 40Ahr lithium will be equiv to an 80Ahr LA but that is not quite right. Ok, the LA will give you 40Ahr of usage but I dont like cycling LAs down to 50%. The Li shouldnt really be taken down below 20% unless you have a rock solid BMS that stops you screwing up. At the top end, unless you have a rock solid BMS then you can also screw up. I would therefore think you will be lucky to get 30Ahrs use out of the 40Ahr bank....but I think you are avoiding the 'perils' of going up to 100%. Phone chargers, RC aircraft chargers etc are designed to get Li banks up to 100% and then turn off. On boats though, we dont have these sophisticated chargers and SoC monitoring that allows us to accurately get to 100% so the tendancy is to go to 80-90% charge. Your system then is part way between the 'heavy duty' Li for boats duty and the duty for a RC aircraft where 100% SoC is typical. I would be concerned that you are relying on a charger to terminate charge when you really need more control.

Also the low Ahr of the bank will cause issues if you are charging by solar. You dont say how much solar you have but 500W of panels used to give us a 30A charge in full sun in summer. If you have a 40Ahr bank, the solar will fill it in less than an hour in these conditions so how do you propose to make sure you control SoC termination under these conditions? Most controllers go to float far too early so you may only have 32Ahrs in when the MPPT goes to float....so even less capacity to use.

Is there another way to get what you want? I am not sure how much you are paying for these cells but why not think about buying a used Relion 12V battery from Peter's mate? <£400 and just hook that up to your existing battery set up. It would be just light enough to carry from boat to boat. Maybe need a rethink on charging but it would certainly store more solar energy.

[magnetman]

I am specifically looking to make myself a portable mains energy storage package. 

 

I won't need it in summer, can just use it as an extra power pack for my electric canoe and recharge on solar, but for winter when I am unwilling to run the engine solely to generate power it makes sense to import the stored mains electric and use it over the weekend that I am on the boat. 

 

The RC hobby chargers seem to have programmable limits on voltage so I think I would trust it not to over charge. And i'd be on top of the thing when discharging anyway so can do manual management and like I said the mppt  LVC via a relay and solenoid would probably sort the low voltage problem fairly reliably. 

 

And I'm not buying used batteries. 

 

It's an unusual way to do if but I reckon it'll work.