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Balancing troubles...
#21
"In bypass" will trigger whatever output you've picked, when any mon goes into bypass 

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#22
Awesome, thanks.... All setup, just got to find some small 12v fans that I can cable tie onto the blockmons somehow

(05-23-2019, 11:05 PM)Redpacket Wrote: I cool my 'mons with a 12V fan triggered by the "cooling enabled" state with the default output relay.
My WM1 doesn't seem to be able to switch the MOSFET outputs based on temp (would prefer this but it didn't seem to work).

With the last pics you're showing this shows a mis-match between the voltages the Outback MPPT & the blockmons are set to.
The pack is in balance & you're still pushing the blockmons quite hard.
You need to back down the charge voltage a bit.

It's a bit of a pain, you need the balance current but don't want to cook the blockmons too hard/too often/too long.

You really, really need to stop the cells getting to 3.75V thing, those cells will die soon.

I've run a few days at absorb set to 55.5v with 12 minute absorb timer. Haven't had any problems with cells going high, and cells 6 & 14 are coming up nicely.

These cells are CALB and the pack they came from were run up to 4.1/cell which the pack builder thought was ok. This was a reputable pack builder (Axeon, got bought by Johnson Mathey, now owned by Cummins).

Just need to sort out some mon cooling fans.
Current system: 9.6kWh wet Nicad batteries, 16S1P Calb LiFePo4 210aH, Batrium WM4, Outback vfx3048 inverter, mx60 mppt controller, flexware 500 mounting hardware, 2.4kW solar array, 6kW lister diesel genset. MY'13 Vauxhall Ampera
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#23
I've got I2C temperature sensors on each mon so only the fans that need to be on, are on when cooling is called for.
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#24
(05-23-2019, 11:05 PM)Redpacket Wrote: I cool my 'mons with a 12V fan triggered by the "cooling enabled" state with the default output relay.
My WM1 doesn't seem to be able to switch the MOSFET outputs based on temp (would prefer this but it didn't seem to work).
I use the "Bypass Temp Limit" to lower heat in the longmons and tuned the system to avoid using bypass under normal circumstances.
Enabled auto-level for a few days last month and it tightened things up nicely (back to 50mv difference) - but then turned it off again with the goal of not using longmons in bypass unless necessary. Necessary ~ 100mv or greater difference between packs.
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#25
You've got to properly, independently confirm the these pack voltages asap!
If you have LiFePo4 cells, getting to 4.1V/cell = cell destroyed, catastrophic venting, risk of fire, definite swollen cells.
If they are LiFePo4 & a supplier told you 4.1V is OK, they're insane!
read this thread, his 200AHr cells were destroyed:
https://secondlifestorage.com/t-Choice-o...8#pid49958

If the cells are not LiFePo4 and are Li-Ion instead like most 18650's then 4.1V is an ideal voltage.

Calb cells are usually LiFePo4 not Li-Ion.

Bypass temp limit is OK & good to set, I've got this set to 60degC.
With the fan cooling,the longmons stay much cooler & you can bypass more without them getting too hot.
But it's OK & normal for bypassing to operate - if it doesn't, the pack is not balancing & will eventually drift out of balance.
Here's my settings:
 
& here's "auto leveling" in action after a week of not quite getting to 100%
Note the bypassing looks strong but each cell only stays at the high current for about 25 secs (as set) because the auto leveling "rolls through" the pack, I see the "bunch" of red bypassing cells step to the right every few seconds (missing low cells as it should).
Running off solar, DIY & electronics fan :-)
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#26
A little more info on voltages to run your LiFePo4 pack at:
https://www.powerstream.com/lithium-phos...oltage.htm
If you look at the tables you only get a few % of extra capacity but the battery life will be shortened because you're pushing the chemistry off the "plateau" where gassing can occur.
Running off solar, DIY & electronics fan :-)
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#27
I know there is no point going above 3.55/cell for capacity reasons. That's why I've tuned absobtion down a bit to what should even out at 3.46v/cell. Got the fm60 set to 55.4 now which works out at 55.45v at the wm4. Unfortunately, you can only tweak the fm60 in 100mv steps.

What do you have your absorbtion setpoint at for your 48v pack?

You mention independently verifying cell voltage under charge, I'll do this when I am back on site with a multimeter. Although I would expect the accuracy of the a2d on the mons to be better than my out of calibration 30yr old fluke.

I use auto levelling too, it seems to do a good job, I start it at 85%SOC.

Here are a couple of screen grabs from Fridays charge session, things settled down nicely after dropping to float and I'm no longer seeing the issue of the top cells drifting up when cell 14 just stayed low. As I said, all I've done differently now is set the bypass voltage to a sensible value above my target cell voltage (which I wasn't doing before) so my mons don't all sit there cooking during absorbtion, and I've dropped the absorbtion setpoint down.





If I wanted to replace the fm60 with something that can talk to the wm4 over canbus, and use the wm4 targets to control charge current etc, what options are there? I need 150v maximum string voltage and it needs to handle 2.5kW of panels, which on a cold, bright, winter's day will hit 2.8kW...
Current system: 9.6kWh wet Nicad batteries, 16S1P Calb LiFePo4 210aH, Batrium WM4, Outback vfx3048 inverter, mx60 mppt controller, flexware 500 mounting hardware, 2.4kW solar array, 6kW lister diesel genset. MY'13 Vauxhall Ampera
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#28
(05-25-2019, 11:27 PM)OffGridInTheCity Wrote: I use the "Bypass Temp Limit" to lower heat in the longmons and tuned the system to avoid using bypass under normal circumstances.

Bypass temp limit just lowers the point at which they'll go into thermal bypass, when that occurs you'll be seeing a voltage rise (uncontrolled) in that cell - that's a bad thing. Cells going into bypass as part of a controlled charge is just a part of a normal charge session, if you actively avoid this occuring your pack will unbalance and you wont be making maximal use of each cells capacity- that's a bad thing.

Unless you've found somehow to turn on cooling when thermal bypass occurs ?

The Victron MPPTs play well with the WM4, but you'll need a Venus device to enable it - I have a few 250/100s - you might get away with their 150 volt versions.

(05-26-2019, 06:35 AM)HughF Wrote: As I said, all I've done differently now is set the bypass voltage to a sensible value above my target cell voltage ....

Perhaps I've misunderstood what you've actually done, but you should be setting the bypass voltage at exactly your target cell voltage.
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#29
(05-26-2019, 06:45 AM)Sean Wrote:
(05-25-2019, 11:27 PM)OffGridInTheCity Wrote: I use the "Bypass Temp Limit" to lower heat in the longmons and tuned the system to avoid using bypass under normal circumstances.

Bypass temp limit just lowers the point at which they'll go into thermal bypass, when that occurs you'll be seeing a voltage rise (uncontrolled) in that cell - that's a bad thing. Cells going into bypass as part of a controlled charge is just a part of a normal charge session, if you actively avoid this occuring your pack will unbalance and you wont be making maximal use of each cells capacity- that's a bad thing.

Unless you've found somehow to turn on cooling when thermal bypass occurs ?

The Victron MPPTs play well with the WM4, but you'll need a Venus device to enable it - I have a few 250/100s - you might get away with their 150 volt versions.

(05-26-2019, 06:35 AM)HughF Wrote: As I said, all I've done differently now is set the bypass voltage to a sensible value above my target cell voltage ....

Perhaps I've misunderstood what you've actually done, but you should be setting the bypass voltage at exactly your target cell voltage.

I found if I set the bypass voltage to my target cell voltage, I end up driving the mons too hard and they thermally reduce their bypass curent, which in turn ends up allowing those cells to float up and stuff gets unbalanced.

Which highlights my underlying problem which I now understand - I need to cool my mons, and I really need to reduce my charge current when I'm heading into bypass. The latter can be sorted with either a new mppt charge controller, or setting a much lower absorbtion setpoint with a longer timer, so it only balances at the end of a longer CV period.

I need some time in front of the system to play with the latter strategy I think.
Current system: 9.6kWh wet Nicad batteries, 16S1P Calb LiFePo4 210aH, Batrium WM4, Outback vfx3048 inverter, mx60 mppt controller, flexware 500 mounting hardware, 2.4kW solar array, 6kW lister diesel genset. MY'13 Vauxhall Ampera
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#30
My understanding of bypass temp limit is it protects the longmon by capping the temp rise.

Like you, I found various voltage reading differences between gear & have had to get used to this too!

Re the bypass & charger voltages it takes some trial & error to tune it to the knee point of your particular pack.
When it's just right, I get some light bypassing (maybe 10-20% red bar) + auto leveling when the batteries are "full".
As said earlier, as soon as any bypassing starts, I have the logic turn on a cooling fan.

When I first set up my packs I saw some voltage rise on one or two cells (got to about 3.6V/cell I recall) - I didn't like this so started tweaking the bypassing & charge voltages.
Here's my notes on that process:
2018-02-14  dropped the absorb from 55.25 (3.453V/cell) to 54.75 (3.421V/cell),
+ dropped the float from 54.5 (3.406V/cell) to 53.75 (3.360V/cell),
2018-02-18  raised the float to 54.25 (3.391V/cell), absorb to 54.75 (3.422V/cell)
2018-03-04  cells 29, 38 still a bit low on float, equal on load, ie undercharged
2018-03-04  raised the float to 54.50 (3.406V/cell), absorb to 54.80 (3.425V/cell)
2018-03-10  cellmon #10 replaced, cells 29, 38 have nearly caught up, cell 38 still a bit behind
tweaked float to 54.40 (3.400V/cell), absorb to 54.50 (3.406V/cell)
2018-03-25  cell #38 still a bit behind, tweaked float to 54.45 (3.403V/cell), absorb to 54.55 (3.409V/cell)
2018-04-01  cell #38 further behind, tweaked float to 54.55 (3.409V/cell), absorb n/c 54.55 (3.409V/cell)
2018-04-04  cell #38 seems to have caught up OK, all cells in bypass 1 or 2 rising,
tweaked float back to 54.45 (3.403V/cell), absorb n/c 54.55 (3.409V/cell)
2018-04-12 cell #38 dropped behind again tweaked float to 54.50
2018-04-15 cell #38 caught up, tweaked float to 54.47 as too much bypassing happening
2018-09-12 bypassing too hard still , float to 54.42, abs to 54.51  eq V = abs
might not be balanced between chargers
2018-09-15  cell 38 low again + might not be balanced between chargers tweaked other MPPTs float to 54.44V
2018-09-30  cell 38 low again + might not be balanced between chargers tweaked other MPPTs float to 54.46V
(since then seems to have been good, current state is float = 54.42, absorb = 54.51)
Now cells track up & down together pretty well & if there's be a cloudy day or two they'll re-balance a bit next time they get to 100%.

I have two different battery constructions, both are in steel cases, this one the cells are a pretty tight fit & there was no room for the longmons in the case.
So I ended up with the longmons packed together, increasing the need for cooling. The clear plastic is polycarbonate & has a gap at the bottom.

So I made this fan housing with 120mm 12VDC PC fans, "corflute" sheet & hot melt glue:

With the control logic, seems to really help keep the temps down.
Running off solar, DIY & electronics fan :-)
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