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Batrium: Using multiple mons to increase total bypass current.
#1
Has anyone implemented (in a production system) multiple mons on a single cell in order to increase the total per cell bypass current as per Daniels recomendation in a related thread ?

(08-15-2019, 05:31 AM)daromer Wrote: From batrium you can balance 10A from a single cell if you want. Just add 10 longmons as example.

For continues 1A per longmons is rather normal. (Depending on ambient temperature and how you mount them)
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#2
Saw a youtube by @HBPowerwall using multiple longmons on a pack - which opened my eyes to this concept.
I understand that it would 'mess up' the nice display as you wouldn't have 1 blue bar to 1 pack anymore...   but that's not a big deal.

I do wonder about the "Nom Series" setting....


Don't understand exactly what Nom Series affects and therefore not sure how multiple mons would affect things.  For example, do you need 'equal number' per pack or can you have 3 on 1 pack and 2 on another...  kind of thing?

Great question!
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#3
My question relates to a single cell, and the use of multiple mons to increase the bypass current of that single cell - the nominal series feature allows for the introduction of addition cells, or packs of cells into an existing system as being nominally in series (when they are actually electrically in parallel).

This is the thread from which my question came ....

https://secondlifestorage.com/t-BMS-inte...tem-design
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#4
(08-16-2019, 03:41 PM)Sean Wrote: My question relates to a single cell, and the use of multiple mons to increase the bypass current of that single cell - the nominal series feature allows for the introduction of addition cells, or packs of cells into an existing system as being nominally in series (when they are actually electrically in parallel).

This is the thread from which my question came ....

https://secondlifestorage.com/t-BMS-inte...tem-design

>How do you ensure that all mons turn on at exactly the same voltage 
The "10 mons" are connected to the same pack or cell, so they see the same voltage (+/- a very small variation I'm sure) and will balance (or not) simultaneously.
Not sure I'm understanding the question as I know you are very experienced.

>the nominal series feature allows for the introduction of addition cells, or packs of cells into an existing system as being nominally
Yes, I get this but this is done by counting mons (I believe).  So if you have 14s  and 14mons and you add 3 more to a pack you'll have 17mons.  So what happens if you have 17mons and set nominal to 14...    seem like this might affect something in Batrium settings.  That's what I'm asking about.
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#5
(08-16-2019, 05:48 PM)OffGridInTheCity Wrote: The "10 mons" are connected to the same pack or cell, so they see the same voltage (+/- a very small variation I'm sure) and will balance (or not) simultaneously.

... that small variation means that they dont start bypassing simultaneously, the only way they will all go into bypass is if the cell voltage is allowed to rise.
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#6
To me the Idea of them turning on at exactly the Same time is not an issue. With long Mons they are totally isolated units. if the voltage gets above your set voltage it turns on. pulls down for Some time until a desirable voltage is reached and then disconnects. If for Example you have 2 longmons on a single Cell and say for example that they are Off in their voltage readings by .01V

So Cell actual get above your set point of 4.1v (4.105v) and Longmon 1 Sees it as 4.11v and turns on and Longmon2 Sees it as 4.099v and does nothing.
Result you get you to 1A of dissipation

No problems as it's only slightly above your setpoint

Now for example your charging your pack at 100A and one cells gets to be full and goes over the 4.1 buy say .25V then Both Longmons will be on and discharging 2A

Yes longmon2 will disconnect slightly later but the tolerance in the longmons has been really close and the only person I recall that had an issue with one reporting out of spec got new ones from Batrium.
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#7
(08-16-2019, 06:07 PM)jdeadman Wrote: Now for example your charging your pack at 100A and one cells gets to be full and goes over the 4.1 buy say .25V then Both Longmons will be on and discharging 2A

I mentioned in the other thread that the only scenario where that I could envisage multiple mons being of productive use would be when charging at a high rate, with a charger outwith BMS control, even when in bypass - I would hope no one would do that without cooling as the mons will fry and thermally bypass - which at 100A would be fraught - I'd also expect that no one would allow a cell to reach 4.1v + .25v

Charge rate would ordinarily be in limited mode when any cell is bypassing - the only advantage of not limiting, and bypassing significant amps would be if cell imbalance was significant, which points to a capacity difference - high rate balance charging isn't a sensible method of masking cell capacity mismatches.
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#8
(08-16-2019, 06:07 PM)Sean Wrote:
(08-16-2019, 05:48 PM)OffGridInTheCity Wrote: The "10 mons" are connected to the same pack or cell, so they see the same voltage (+/- a very small variation I'm sure) and will balance (or not) simultaneously.

... that small variation means that they dont start bypassing simultaneously, the only way they will all go into bypass is if the cell voltage is allowed to rise.

If you have 10mons on a pack and the 1st one (that turns on) is powerful enough to bring down the voltage (within specs of 10mv) so the rest aren't needed - then balance success.   If the 1st one cannot handle it - then 2nd, 3rd etc would turn on until the voltage went down to the desired level.   If all 10 tun on within 10mv difference, then balance is just faster.   Either way it seems like the goal of 10 would be to add extra capacity to balance faster, not necessarily that all 10 would go into bypass instantly/simultaneously on <10millivolt difference.
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#9
Cell voltage needs to be rising in order for multiple mons to all switch on - with large capacity cells a few fractions of a volt is significant.

A rise in voltage above a target indicates an excessive charge current - bypassing that excessive current through a resistive component isn't a productive use of available energy. Bypassing numerous amps via thermal energy is just daft ..... but each to their own etc.

Charging at high rates using a charger that isnt under BMS control is dangerous, limiting the charge rate when in bypass is a fairly well established norm, which is why any competent BMS will be able to signal to a compatable charger a limited charge rate - it's a safety feature, which is why I'm still pondering why anyone would consider multiple mons to increase the bypass current.

I raised the question about bypassing significant amps, by using multiple mons simply as I was curious to see who, and if anyone was using such a configuration in a genuinely productive and effective manner.
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#10
(08-16-2019, 07:22 PM)Sean Wrote:
(08-16-2019, 06:07 PM)jdeadman Wrote: Now for example your charging your pack at 100A and one cells gets to be full and goes over the 4.1 buy say .25V then Both Longmons will be on and discharging 2A

I mentioned in the other thread that the only scenario where that I could envisage multiple mons being of productive use would be when charging at a high rate, with a charger outwith BMS control, even when in bypass - I would hope no one would do that without cooling as the mons will fry and thermally bypass - which at 100A would be fraught - I'd also expect that no one would allow a cell to reach 4.1v + .25v

Charge rate would ordinarily be in limited mode when any cell is bypassing - the only advantage of not limiting, and bypassing significant amps would be if cell imbalance was significant, which points to a capacity difference - high rate balance charging isn't a sensible method of masking cell capacity mismatches.
Sean, aside from victron (I assume they have this feature), do you know of any other mppt controllers that are supported over can or 485 from the watchmon, so they can have their charge rate reduced when bypassing? As you know, I use an fm60 and that is pretty dumb to the outside world. It has taken many months of tweaking to get my voltage settings to the point where I get as much charge as I can into my cells without cooking my mons.
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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