Lithium charging via large alternator ?

[MtB]

41 minutes ago, ditchcrawler said:

And I thought one of their selling points is you can do what you like to them and they just keep going

 

This couldn't be more wrong.

 

They are desperately easy to wreck by overcharging, or undercharging, or charging below 0 degrees C, or letting the cells get wildly out of balance, or by float charging them, or letting them get too hot, or, or.....

 

 

Edited May 31, 2019 by Mike the Boilerman

[peterboat]

36 minutes ago, ditchcrawler said:

And I thought one of their selling points is you can do what you like to them and they just keep going

Never above 80% or below 20% and they will last a very long time abuse them and they wont, it isnt hard and in my case they will last my lifetime whats not to like?

[Dr Bob]

On 31/05/2019 at 16:44, Mike the Boilerman said:

 

This couldn't be more wrong.

 

They are desperately easy to wreck by overcharging, or undercharging, or charging below 0 degrees C, or letting the cells get wildly out of balance, or by float charging them, or letting them get too hot, or, or.....

 

 

No Mike. They are desperately easy to keep between 20 and 80% so you never get into the regimes where problems occur. I know I have only had mine for 6 weeks of CC'ing but they are so much easier than LA to manage.

[Col_T]

Using LA as a dump load for when the lithium battery is charged to the specified level - does anything need to use the LA as a source, or is it in the design purely to receive the alternator trickle charge once the lithium charge is complete?

 

[MoominPapa]

36 minutes ago, Col_T said:

Using LA as a dump load for when the lithium battery is charged to the specified level - does anything need to use the LA as a source, or is it in the design purely to receive the alternator trickle charge once the lithium charge is complete?

 

The way I've done it is that everything (engine loads, domestic loads, alternator and starter) are connected direct to the single LA battery. Apart from the domestic loads, it looks like what you'd find in any car. The Lithiums are paralleled with the LA using a contactor controlled by the BMS. Opening this contactor achieves charge termination when the Lihium bank is full, and once that happens the alternator continues to supply the loads. Once the engine stops, (or a very large load is imposed, larger than alternator output) the BMS notices that the LA voltage has dropped below the Lithium bank voltage and reconnects. This is working very well.

 

When the lithium bank is empty, the BMS similarly opens the contactor to save the bank from over discharge. This leaves the load on the LA battery, which might mean a flat start battery, but also means that the lights won't go out without warning. The BMS sounds a very loud alarm in this case.

 

MP.

 

[Dr Bob]

41 minutes ago, Col_T said:

Using LA as a dump load for when the lithium battery is charged to the specified level - does anything need to use the LA as a source, or is it in the design purely to receive the alternator trickle charge once the lithium charge is complete?

 

Yes, purely to receive the alternator trickle charge. We have 6*110Ahrs of LA and 480Ahrs of Li's wired in parallel. If I use 70% of the Li charge the voltage is down to 12.7V and then the LA's start to give power in addition to the Li's. Once you disconnect the Li bank on charging the alternator just tries to charge the LA bank as normal. No drama.

[Col_T]

Thanks, chaps. It all becomes clearer bit by bit!

 

[MtB]

1 hour ago, Dr Bob said:

No Mike. They are desperately easy to keep between 20 and 80% so you never get into the regimes where problems occur. I know I have only had mine for 6 weeks of CC'ing but they are so much easier than LA to manage.

 

Only desperately easy if you are actually there to do the managing, Shirley!

 

When I leave my bote, I often have no idea whether I'll be back in seven hours or in seven days. So to get around this I thought I should just isolate the lithiums when I leave the bote.

 

But what if I forget and we have a few sunny days? ???... One solution to this would be another internet-controlled switch the same as I use to operate the Whispergen, but use it to operate a relay that operates a contactor that isolates the lithiums. Then I only have to hope the internet connection stays up and running.....

 

 

[MoominPapa]

26 minutes ago, Mike the Boilerman said:

 

Only desperately easy if you are actually there to do the managing, Shirley!

 

When I leave my bote, I often have no idea whether I'll be back in seven hours or in seven days. So to get around this I thought I should just isolate the lithiums when I leave the bote.

 

But what if I forget and we have a few sunny days? ???... One solution to this would be another internet-controlled switch the same as I use to operate the Whispergen, but use it to operate a relay that operates a contactor that isolates the lithiums. Then I only have to hope the internet connection stays up and running.....

 

 

You have a battery management system that's capable of doing charge termination and does so at the relevant point.

 

MP.

 

[Dr Bob]

41 minutes ago, Mike the Boilerman said:

 

Only desperately easy if you are actually there to do the managing, Shirley!

 

When I leave my bote, I often have no idea whether I'll be back in seven hours or in seven days. So to get around this I thought I should just isolate the lithiums when I leave the bote.

 

But what if I forget and we have a few sunny days? ???... One solution to this would be another internet-controlled switch the same as I use to operate the Whispergen, but use it to operate a relay that operates a contactor that isolates the lithiums. Then I only have to hope the internet connection stays up and running.....

 

 

Don't forget!

 

It becomes the same behaviour as locking the front door.....

 

......and I have the auto disconnect.

[MtB]

15 minutes ago, MoominPapa said:

You have a battery management system that's capable of doing charge termination and does so at the relevant point.

 

MP.

 

 

Do I?

 

Its a Tracer 2215BN. I'll have another read of the manual.

 

 

[MoominPapa]

1 hour ago, Mike the Boilerman said:

 

Do I?

 

Its a Tracer 2215BN. I'll have another read of the manual.

 

 

That's a solar charge controller, yes?  The general wisdom is that you need a Battery Management System that monitors the batteries, and tells the charge controller when to shut off, or disconnects the batteries itself. Such controller should be capable of measuring individual cell voltages and the current through the battery (which is not necessarily the same thing as the output from the solar system.)

 

MP.

 

[MtB]

51 minutes ago, MoominPapa said:

That's a solar charge controller, yes?  The general wisdom is that you need a Battery Management System that monitors the batteries, and tells the charge controller when to shut off, or disconnects the batteries itself. Such controller should be capable of measuring individual cell voltages and the current through the battery (which is not necessarily the same thing as the output from the solar system.)

 

MP.

 

 

Err.... I thought we were discussing Dr Bob's suggestion they could be managed manually, without all that stuff....

 

 

 

[MoominPapa]

24 minutes ago, Mike the Boilerman said:

 

Err.... I thought we were discussing Dr Bob's suggestion they could be managed manually, without all that stuff....

 

 

 

My mistake. My take is that it needs to be automatic.

 

MP.

 

[MtB]

6 minutes ago, MoominPapa said:

My mistake. My take is that it needs to be automatic.

 

MP.

 

 

Never mind. Like Dr Bob I am happy to manage my batts by just keeping an eye on the voltage, after all it only changes very slowly I imagine. I was musing about how to manage the solar when I'm away for extended periods. Dr Bob says just NEVER forget to turn it off before going out. I'm not sure I'm that clever....

 

 

[MoominPapa]

14 minutes ago, Mike the Boilerman said:

 

Never mind. Like Dr Bob I am happy to manage my batts by just keeping an eye on the voltage, after all it only changes very slowly I imagine. I was musing about how to manage the solar when I'm away for extended periods. Dr Bob says just NEVER forget to turn it off before going out. I'm not sure I'm that clever....

 

 

 You imagine wrong. The voltage under charge stays flat for most of the charge cycle, then rises very fast as the final one or two percent are added. It's also quite possible to overcharge a LiFePo4 cell without ever getting the voltage up to the limit. A modest charge from solar will keep charging the cell without increasing the voltage, to beyond 100% charge, eventually.

 

MP.

 

[Dr Bob]

3 hours ago, Mike the Boilerman said:

 

Never mind. Like Dr Bob I am happy to manage my batts by just keeping an eye on the voltage, after all it only changes very slowly I imagine. I was musing about how to manage the solar when I'm away for extended periods. Dr Bob says just NEVER forget to turn it off before going out. I'm not sure I'm that clever....

 

 

.....but do you always remember to lock your doors?

 

When first installed, I isolated the bank every time I left the boat. Now I only ever do that if we are leaving it overnight as we are always at least 100Ahrs from full so solar is never going to overcharge it....and if the Amps were that high from solar it would trip the voltage relay when approaching full and auto disconnect. 

I could set my over voltage at 13.5V and it wouldn't have tripped in the last 6 weeks....which would likely catch any over charging by solar. It really isn't a drama.

 

[MtB]

4 minutes ago, Dr Bob said:

.....but do you always remember to lock your doors?

 

When first installed, I isolated the bank every time I left the boat. Now I only ever do that if we are leaving it overnight as we are always at least 100Ahrs from full so solar is never going to overcharge it....and if the Amps were that high from solar it would trip the voltage relay when approaching full and auto disconnect. 

I could set my over voltage at 13.5V and it wouldn't have tripped in the last 6 weeks....which would likely catch any over charging by solar. It really isn't a drama.

 

 

I need to try this and get to know my voltages. Having a cheap second hand set of cells its not a great disaster if I end up wrecking them, just very annoying. 

 

How does your comment square with received wisdom that 101% SoC can be achieved and batts wrecked with long term trickle charging (from say, solar) without the voltage ever rising to trip voltage? As explained by MP in post 66 above your post. 

[MtB]

 

 

3 hours ago, MoominPapa said:

You imagine wrong. The voltage under charge stays flat for most of the charge cycle, then rises very fast as the final one or two percent are added.

 

I actually meant track the SoC by voltage during resting and discharge states. Will that work? Is there much droop when batts are delivering (sensibly low) current?

 

I guess I am imagining AH counting with the BMV when charging, and SoC measuring using voltage when not charging. 

 

One more question... Does Mr Peukert interfere when drawing larger currents from lithiums? (Not that I plan to.)

 

 

[peterboat]

5 hours ago, MoominPapa said:

That's a solar charge controller, yes?  The general wisdom is that you need a Battery Management System that monitors the batteries, and tells the charge controller when to shut off, or disconnects the batteries itself. Such controller should be capable of measuring individual cell voltages and the current through the battery (which is not necessarily the same thing as the output from the solar system.)

 

MP.

 

I leave my Midnite controller o its own devices, up to press its done well, I see 13.8 volts, then it goes into float at 13.6 and thats it nothing going in until the fridge draws enough, but it seems to stay in float mode so the batteries remain protected. I recently checked the batteries for balance and they were all good, so for me i will forgo the external BMS systems and stay with limiting the voltage to a maximum of 13.8 volts. I know it makes sense

[MoominPapa]

9 minutes ago, Mike the Boilerman said:

 

I actually meant track the SoC by voltage during resting and discharge states. Will that work? Is there much droop when batts are delivering (sensibly low) current?

Almost none. They have a terrifyingly small internal resistance.

9 minutes ago, Mike the Boilerman said:

I guess I am imagining AH counting with the BMV when charging, and SoC measuring using voltage when not charging. 

Why not track discharge via AH counting too. The discharge voltage curve is very flat, so getting an accurate metric from that is diffiicult.

9 minutes ago, Mike the Boilerman said:

 

One more question... Does Mr Peukert interfere when drawing larger currents from lithiums? (Not that I plan to.)

The Peukert exponent is very close to one. For fractional-C discharges it can be ignored.

 

MP

5 minutes ago, peterboat said:

I leave my Midnite controller o its own devices, up to press its done well, I see 13.8 volts, then it goes into float at 13.6 and thats it nothing going in until the fridge draws enough, but it seems to stay in float mode so the batteries remain protected. I recently checked the batteries for balance and they were all good, so for me i will forgo the external BMS systems and stay with limiting the voltage to a maximum of 13.8 volts. I know it makes sense

It's not clear from this how the controller exits float mode. At 13.8v a LiFePO4 bank will continue to charge and may be overcharged, so leaving float mode too early would be bad.

 

MP.

 

[peterboat]

Bob and I have discovered that these batteries are very easy to live with, my solar controller works well and the Whispergen does as well, as its charge settings are easy to set and work well, so I just dont see over 13.8 volts, which then drops into float, a check on the puter proves this is correct, I am not worried about squeezing the last amp from the batteries as this shortens their life.

[MtB]

2 minutes ago, MoominPapa said:

Almost none. They have a terrifyingly small internal resistance.

Why not track discharge via AH counting too. The discharge voltage curve is very flat, so getting an accurate metric from that is diffiicult.

The Peukert exponent is very close to one. For fractional-C discharges it can be ignored.

 

MP

 

Ok fanx. This seems a Good Idea.

 

I imagine I can use carefully approached high states of charge and discharge (recognised with voltage) combined with AH counting to determine the actual capacity of the bank, then just use the AH counter to know SoC on a day-to-day basis. Unusually low or high voltages being the Big Red Light that the AH counting is going wrong.

 

Cell balance monitoring also needs considering....

 

[peterboat]

6 minutes ago, MoominPapa said:

Almost none. They have a terrifyingly small internal resistance.

Why not track discharge via AH counting too. The discharge voltage curve is very flat, so getting an accurate metric from that is diffiicult.

The Peukert exponent is very close to one. For fractional-C discharges it can be ignored.

 

MP

It's not clear from this how the controller exits float mode. At 13.8v a LiFePO4 bank will continue to charge and may be overcharged, so leaving float mode too early would be bad.

 

MP.

 

Andy it doesnt, I have watched it numerous times and I have watched it in the early days on the puter, now days I dont bother it just happens

[peterboat]

7 minutes ago, Mike the Boilerman said:

 

Ok fanx. This seems a Good Idea.

 

I imagine I can use carefully approached high states of charge and discharge (recognised with voltage) combined with AH counting to determine the actual capacity of the bank, then just use the AH counter to know SoC on a day-to-day basis. Unusually low or high voltages being the Big Red Light that the AH counting is going wrong.

 

Cell balance monitoring also needs considering....

 

How many batteries do you have Mike? if its only a few a couple of cheap lcd gauges and rotary switches will do the job