MPPT or PWM charger? For LiFePO4 battery?

[T1 Terry]

Unsure if I should be posting this link, but there are manufacturers supplying LiFe batteries with BMS, I wonder if anyone has any experience with batteries from this supplier, good or bad.

These 2 lines from the PDF tell me they either haven't got a clue or they are scare mongers Why a Battery Management System (BMS) is needed:
1. A LFP cell will be destroyed immediately if the voltage over the cell falls to less than 2,5V.
2. A LFP cell will be destroyed immediately if the voltage over the cell increases to more than 4,2V.


This of course pure and utter nonsense so I stopped reading at about that point. It's a pity because Victron have a great reputation for selling quality equipment so I don't undrstand why they would be putting such nonsense forward trying to pass it off as fact. Simple too much of this nonsense out there, all from BMS sellers.

T1 Terry

[Beanyboy57]

Link to advertisement

Hi Williams,

I'm also looking for a charger solution or provider. Would you please share with me once you get any update? I'll do the same for sure.

Since I'm designing a standalone solar generator for disaster recovery, I am keen to integrate LiFePO4 into my system in order to replace the Lead acid type.

with kind regards
Thomas

Unsure if I should be posting this link, but there are manufacturers supplying LiFe batteries with BMS, I wonder if anyone has any experience with batteries from this supplier, good or bad.

[rreinha]

Hi all,
I have a 60V/24Ah li-ion battery 16S/6P coming from my e-scooter. It can't anymore provide enough current for the scooter (25-50A), but it can easily provide 4-5 A I need to turn on my fluorescent lights (100 W in total at 230V).
I also have two 240 Wp solar panels, which currently charge two 12V/65Ah Pb-gel batteries using a "standard" charge regulator.

How could I "move" my system to lithium so I can count on 1440 Wh rather than 780 Wh?

I read somw of you use lead chargers with lithium battery "equipped with balancer and BMS" and whatelse.
Does it exist a ready-made solar-lithium charge regulator for 60V batteries?
Or, which is the alternative?

This pack in a brand new state was only 1200Wh, the 60V label is at full Charge (3.75/cell) and not the nominal of 51V. New it should have produced 2200W for 45 minutes, until 44V.
I suspect the BMS is very limited on what it does and I agree with Ti Terry, that you may have a few 0V cells, sometimes you can re-charge them (IF THERE ARE LFP) and have no huge negative effect. BUT If they have any Cobalt in them DON'T try to charge them (BANG!).
Do you know the scooter maker name?

[T1 Terry]

I would first check the voltages of all the Li cells at the end of charge. there is a very big chance the BMS has failed to properly balance the cells and some of the cells are just flat. Charge each cell seperately to 3.6v till no more amps flow into that cell, then try the scooter again. If it still doesn't work properly check all the cell voltages, when the scooter seems sluggish before recharging, number each cell and post what the voltages are and I will see if I can help you build a hose battery from the old cells that are still any good.

T1 Terry

[Sunking]

Hi all,I have a 60V/24Ah li-ion battery 16S/6P coming from my e-scooter.

So why are you HJ an old thread?

[inetdog]

Hi all,
I have a 60V/24Ah li-ion battery 16S/6P coming from my e-scooter. It can't anymore provide enough current for the scooter (25-50A), but it can easily provide 4-5 A I need to turn on my fluorescent lights (100 W in total at 230V).
I also have two 240 Wp solar panels, which currently charge two 12V/65Ah Pb-gel batteries using a "standard" charge regulator.

How could I "move" my system to lithium so I can count on 1440 Wh rather than 780 Wh?

I read somw of you use lead chargers with lithium battery "equipped with balancer and BMS" and whatelse.
Does it exist a ready-made solar-lithium charge regulator for 60V batteries?
Or, which is the alternative?

Hi and welcome to the Forum!

Not very many solar charge controllers come with support for that high a battery voltage. 48 volts is the usual high end. But some do support 60.
If the connection between the battery and the rest of the scooter, including the charger, is only two wires, + and -, then the battery management system, or enough of it for the scooter use case, will be integrated into the battery. The only things that the external charger will have to do is control the voltage and current to the profile needed for that battery.
Without charging information from the battery manufacturer or the scooter manufacturer, it is hard to know what those setting should be.

If the battery is connected by more than just two wires, then it is likely that the charging circuit has to receive and act on information (signals) sent back to it from the battery. This could include an end of charge alert, battery temperature, and a host of other things which a controller not designed for that battery will not be able to process properly.

The other side of the problem will be to find an inverter which can handle 60 volts input to give you 120 or 240 volts out. They exist, but they tend to be either large and expensive or hard to find and expensive.

[jumpjack]

Hi all,
I have a 60V/24Ah li-ion battery 16S/6P coming from my e-scooter. It can't anymore provide enough current for the scooter (25-50A), but it can easily provide 4-5 A I need to turn on my fluorescent lights (100 W in total at 230V).
I also have two 240 Wp solar panels, which currently charge two 12V/65Ah Pb-gel batteries using a "standard" charge regulator.

How could I "move" my system to lithium so I can count on 1440 Wh rather than 780 Wh?

I read somw of you use lead chargers with lithium battery "equipped with balancer and BMS" and whatelse.
Does it exist a ready-made solar-lithium charge regulator for 60V batteries?
Or, which is the alternative?

[steveg]

Just realised I missed a digit in the absorption voltage, it should have been 3.475v. So, 3.5v boost, 3.475v absorption and 3.45v float. surprisingly the batteries will take another 20Ah to 30Ah during that absorption phase but the cells are protected from over voltage, float just keeps them full till the sun goes down.
You can only measure the cell balance of fully charged cells, voltages above 3.45v while being charged at less than 10 amps, if 60 amps were going in it was no where near fully charged at the time you measured the cell balance. If they were 70mV ot of balance at that point you might get a big scare when you see what the imbalance is at fully charged and just how high the high cells go. Anything under full voltage my cells remain within 10 mV

T1 Terry

Hi,

No big scare? - they are always <70mV at any point, the worst case will be under full charge load as this accentuates the cell differences.

My full charge voltage is 3.525V per cell

Regards,

Steve.

[T1 Terry]

Just realised I missed a digit in the absorption voltage, it should have been 3.475v. So, 3.5v boost, 3.475v absorption and 3.45v float. surprisingly the batteries will take another 20Ah to 30Ah during that absorption phase but the cells are protected from over voltage, float just keeps them full till the sun goes down.
You can only measure the cell balance of fully charged cells, voltages above 3.45v while being charged at less than 10 amps, if 60 amps were going in it was no where near fully charged at the time you measured the cell balance. If they were 70mV ot of balance at that point you might get a big scare when you see what the imbalance is at fully charged and just how high the high cells go. Anything under full voltage my cells remain within 10 mV

T1 Terry

[steveg]

Not real keen on full time active BMS, too many reports of lost cells from those type BMS units going astray. I'm more into passive monitoring individual cell voltages with an alarm for over and under voltage of the individual cells, it gives a clear warning if anything needs attention. We found a loose cell linking plate on a 24v nom. bank this way because one set of paralleled cells hit over voltage first every time yet had the lowest voltage every time under high load, basically it was one cell down on capacity.
I set max boost voltage to an average of 3.5v per cell, absorption to 3.75v average and float to 3.45 average. The alarm function catches any runaways but with the way the system set up as a 12v nom. the charging amps when/if the sun appears is between 75 amps and 125 amps so runaways happen very quickly if the cells get too much out of balance. This is the reason for looking at a dump load control into the HWS, better to use the excess solar than waste it. I guess that means I will need to lift the max. boost voltage to 3.6v per cell to ensure the solar excess is used by the HWS, more trialling to do.

T1 Terry

Hi,

I have just measured my cells - with 60A coming in they are all within 70mV of each other - I would rather have a BMS that should wsork for the life o fthe cells than worry about checking them once a month, but hey that's just me. My pack came with everything all ready to go, so this was the easy path US$7k for 48V 300Ah including metal housing and BMS - not too bad I thought.

LiFePO4 should never have absorption - and never above 3.65V per cell, so maybe set absorb to off or to 3.65V/cell and float to same - as there is no 'float' wtih this technology cell - just a thought.


My regulator is set to 56.4V constant voltage with a 60A current limit - simple setup and the BMS handles the over/under charge if that happens.

Regards,

Steve.

[T1 Terry]

Not real keen on full time active BMS, too many reports of lost cells from those type BMS units going astray. I'm more into passive monitoring individual cell voltages with an alarm for over and under voltage of the individual cells, it gives a clear warning if anything needs attention. We found a loose cell linking plate on a 24v nom. bank this way because one set of paralleled cells hit over voltage first every time yet had the lowest voltage every time under high load, basically it was one cell down on capacity.
I set max boost voltage to an average of 3.5v per cell, absorption to 3.75v average and float to 3.45 average. The alarm function catches any runaways but with the way the system set up as a 12v nom. the charging amps when/if the sun appears is between 75 amps and 125 amps so runaways happen very quickly if the cells get too much out of balance. This is the reason for looking at a dump load control into the HWS, better to use the excess solar than waste it. I guess that means I will need to lift the max. boost voltage to 3.6v per cell to ensure the solar excess is used by the HWS, more trialling to do.

T1 Terry

[steveg]

Hi Steve,
If you use accumulative cell voltage as the trigger how do you use any other method to keep the cells in balance?
I'm leaning toward using the alarm port on the Cell Log8 monitors and using 3.8v as a switch point and using a Jay Car timer circuit running the load for 10 mins but I may bring that back to 3.6v and drop the load back to 5 mins each time high voltage is reached, I will need to trial it first. On another forum a member is trialling a kit to control the 240vac side to 1,000w, if this is a winner I can simply switch the water heater on and off and hard wire it into the 5kW output from the inverter. The element in the HWS is a 3.6kW unit so I'm concerned about this load switching on while other loads are already running like the fridges and/or microwave. Possibly making an issue of a non problem as the inverter is 20% overload rated for 30 mins operation making it 6000w max output, allowing for 20% inefficiency at the overload stage makes that a 7200w battery load absolute max. Worst case scenario, at the moment all the loads turned on a cloud blocked the sun stopping any solar input the max battery load would be 140 amps for 10 mins, 23Ah...... If the inverter can handle it I'm sure the batteries will. Inverter temp derating could be the issue...... Might need to keep the 100w controller for the HWS as a back up plan B.

Sorry for the rambling, funny how typing it through here sorts the issues as I go Think I'll copy this post into my personal folder as a reminder of what plan A & B were so if you see bits I’ve got wrong please let me know, personal blinkers to issues can be a real problem sometimes There is no one around here I can bounce ideas off, mention contemplating a 7200w load on a battery bank for 20 mins and their eyes roll.

T1 Terry

Hi,

My pack came wtih a BMS built in it - blog has all the details - http://offgridnz.livejournal.com all I do is hook the solar reg directly to the charge in terminal of the pack and the inverter to the discharge terminal - easy.

The pack has it's own cell balancing circuit - justa few 100 mA current balance, but seems to do the trick lovely - if you want make an flyback converter that'd be the way to go - I was thinking of making such a beast as there seems to be a lack of high performance balancers out there.

You will find the voltages can be tuned fo ryour system for on/off - be sure not to 100% charge your cell too - from what I have read 90% full and 30% empty are good way points for longer life - my full charge (set by regulator) is 56.4V

btw - I have found someone else here in NZ just yesterday with a 48V LiFePO4 system - I will see how his system is configured.

Regards,

Steve.

[T1 Terry]

Cell balancing

Hi Steve,
If you use accumulative cell voltage as the trigger how do you use any other method to keep the cells in balance?
I'm leaning toward using the alarm port on the Cell Log8 monitors and using 3.8v as a switch point and using a Jay Car timer circuit running the load for 10 mins but I may bring that back to 3.6v and drop the load back to 5 mins each time high voltage is reached, I will need to trial it first. On another forum a member is trialling a kit to control the 240vac side to 1,000w, if this is a winner I can simply switch the water heater on and off and hard wire it into the 5kW output from the inverter. The element in the HWS is a 3.6kW unit so I'm concerned about this load switching on while other loads are already running like the fridges and/or microwave. Possibly making an issue of a non problem as the inverter is 20% overload rated for 30 mins operation making it 6000w max output, allowing for 20% inefficiency at the overload stage makes that a 7200w battery load absolute max. Worst case scenario, at the moment all the loads turned on a cloud blocked the sun stopping any solar input the max battery load would be 140 amps for 10 mins, 23Ah...... If the inverter can handle it I'm sure the batteries will. Inverter temp derating could be the issue...... Might need to keep the 100w controller for the HWS as a back up plan B.

Sorry for the rambling, funny how typing it through here sorts the issues as I go Think I'll copy this post into my personal folder as a reminder of what plan A & B were so if you see bits I

[steveg]

Hi Steve, I live not far from the banks of Lake Illawarra just past Wollongong, fairly heavily housed so wood heating isn't really an alternative these days, wood is too expensive.
I have a 48v 5kw UPS inverter charger still in it's box but I still need to better organise how to charge the battery pack at 48v nom. The higher amp draw has little effect on Li batteries, their 3,000 cycles rating is at 0.5C discharge/charge routine and
I certainly couldn't pull that sort of current in a house system.
If I link 4 panels in series to create the 48v nom. the Mpv would be 60v to 68v while the battery voltage would be 51v to 55.2v , not very efficient, then there is the loss of output from 4 panels if one is shaded. I've already been through the MPPT scam and that is the biggest rout since the R12/R134 scandal.
I could run 18 cells for nom. 54v, this would give me a battery range of 57.6v to 62.1v, fairly close to Mpv but running very close to the wire for the inverter over voltage of 64vdc. Something to look at in the new year.

The hot water is solar with manual electric back up, it's a matter of making a switchable system that is triggered by individual cell voltage so I know the batteries are near full before solar generation is wasted heating water. 18 cells creates a logistics problem monitoring and balancing them without going over board with electronic circuitry. After quite a few years in the industrial fitting world and a life time in the automotive world I know just how unpredictable micro processor control is so I'd much prefer not to go down that path.

T1 Terry

Hi T1 Terry,

You live in a lovely part of the word there!

you are best to stick to 16 cells - I use a MPPT controller only because it has current limiting and feedback features not because I expect more power from my panels MPPT benefits are very questionable - I erred to the side of MPPT because it was the newer unit, but I guess PWM would work just as well?

The HW switch over - mine is a 20A insulated triac which is being driven by a opto isolated triac driver - so a small 3v signal can now turn on/off my 3kw element - happy to share the details if you are keen on making a small micro controller board to measure battery voltage and turn element on/off - mine turn on at 55.3V and of at around 53.2V (55.3 is pretty close to full charge)

The 53.2V means that if something else turns on the voltage drop will cause the micro to turn off the element and wait till the voltage gets back to 55.3V.

Regards,

Steve.

[T1 Terry]

Hi Steve, I live not far from the banks of Lake Illawarra just past Wollongong, fairly heavily housed so wood heating isn't really an alternative these days, wood is too expensive.
I have a 48v 5kw UPS inverter charger still in it's box but I still need to better organise how to charge the battery pack at 48v nom. The higher amp draw has little effect on Li batteries, their 3,000 cycles rating is at 0.5C discharge/charge routine and
I certainly couldn't pull that sort of current in a house system.
If I link 4 panels in series to create the 48v nom. the Mpv would be 60v to 68v while the battery voltage would be 51v to 55.2v , not very efficient, then there is the loss of output from 4 panels if one is shaded. I've already been through the MPPT scam and that is the biggest rout since the R12/R134 scandal.
I could run 18 cells for nom. 54v, this would give me a battery range of 57.6v to 62.1v, fairly close to Mpv but running very close to the wire for the inverter over voltage of 64vdc. Something to look at in the new year.

The hot water is solar with manual electric back up, it's a matter of making a switchable system that is triggered by individual cell voltage so I know the batteries are near full before solar generation is wasted heating water. 18 cells creates a logistics problem monitoring and balancing them without going over board with electronic circuitry. After quite a few years in the industrial fitting world and a life time in the automotive world I know just how unpredictable micro processor control is so I'd much prefer not to go down that path.

T1 Terry