Ambrose,
A little more time and reading your response twice and just a few more comments (but not the type to be added to the existing response - miaculpa).
Ambrose said:
The switch I'm using has a center off position so that there would be no direct switching between 37 and 74V. There would be a disconnect from 37V before the switch can go to 74V.
Got it, so XPDT Center Off
That should prevent any chance of shorting going from 37 -> 74 (shorting shouldn't be possible from 74 -> 37v just FTY)
Ambrose said:
I'm not looking for cell level logging since the Sony/Konions are relatively bulletproof.
From what I hear the cells themselves are fairly bullet proof, toolpacks in general the BMSes seem to give some people issues... the charging is what goes goofy on the rest - seems your switch is designed / intended not for the purpose of giving you 2 different maximum speed and thus efficient speed ranges of say 20mph and 40mph but only to facilitate easier charging, retention of factory BMS and simplicity and so on... I can't argue with you here!
Ambrose said:
I'm looking for pack voltages to spot potential problems with any individual cells and the CellLog seems like a perfect candidate for this job.
This is the thing I don't get...
Either you mean individual pack voltages (meaning toolpack 36v 1P readings so 8 in all) but you indicate it's to look for potential problems with any individual "cells" - if by Cells you mean 36v Pack in 1P = 1 Cell okay... If however you mean to spot possible issues within one or another of the Series of 10 cells inside each 36v pack... well that would require bringing out balance taps or wires to get a reading on each cell voltage...
The problem is once you have these Packs in 4P configuration... the best monitoring, display or logging you can do without adding balance taps is:
4P pack level voltage, but you can't guess the cell voltages from this (divide by 10 doesn't do the trick really) and since it has no use for your charging mode of 8P (I assume) you really just get pack level voltage.
Since your goal seems that you want to potentially identify faulty cells, I have some ideas on how you could acheive just this but... they could be complicated to some extent and I don't want to go too deep but I will say that I do agree with the idea and concept - it provides you a chance to yank a bad sub pack and it's mate and keep on going - if you id it in time.
Ambrose said:
I don't need to use 37V with my 72V Lyen's controller. I need the switch so that I can charge at 37V and then flip the switch and run at 74V.
I figured this out finally as elaborated on above... the advantage of this type of system (I'm working one out for 12/24s now) is that your setup may be good for 22mph efficiently at 36v which is enemic but has much better range usually and also is good for throttle tractibility around towns and residential neighborhoods... flipping to 74 volts and the throttle becomes a gun shy child and current draw is enormous off the line... startup in 36v until taper off, flip to 74v when you need the high end speed..
Your Lyen controller could be adapted fairly easily to work from 29v -> 100v (though 98 is the highest I will go) using Knuckles Any Voltage Mod (a Transistor a few diodes and a resistor in place of R1 inside the controller)... then you engage either voltage mode and the controller just keeps on trucking...
This is obviously not what you were after but it would be a nice possible side effect and not difficult to implement.
Ambrose said:
Your solution sounds technically strong, but tough for me to implement. I try very hard to keep the ebike as simple as possible which is why I like BFPs so much. They don't need a BMS to run, but I would love to have an alarm and meter on them just in case they start acting up.
Thank you - I gave it some thought, just not enough
Since there is no way to monitor individual 10S packs voltage levels but only the parallel packs as a whole - the only way you would see an issue would be if a pack flat out failed due to internal BMS... Is that what your thinking, that a pack will cutout and drop to 0v via internal BMS and you want notification of this and some feedback / warning?
Does the internal BMS shut the output of the pack down if the voltage sags too far or a cell is below LVC?
When shutdown, does it interrupt the series connection or leave it in place?
I would assume if you lost 1/4 of your capacity (4P, 1 pack down = 1/4) that if you have a total of 10AH that would be a 2.5AH drop and should result in the effected cluster of 36v via 4P to drop by roughly 25% immediatly...
So assume nominal voltage is currently displayed on Bank #1 (Cell Log #1 Pack #1) and suddenly the voltage drops from 37v down to between 35v and 27.75 but Bank #2 is showing 36v... strong indicator you lost a pack or there is a weak pack... which one, that would require alot more work (doable but more work).
Ambrose said:
You bring up a good point about the CellLog. They can't bridge the pack between 37 and 74V. I will need two CellLogs in order to use it in 74V mode, however, that would allow me to add additional BFPs if I wanted additional range.
They are powered by each 36v subpack so... being isolated they will work in both 37 and 2x for 74v mode... yep 2 cell log8s (and trust me get the logging ones for a few bucks more) (and you do need that for seeing possible loss of 1 of 4 in parallel of any sub pack of BFPs)...
Ambrose said:
Thanks Mike, your questions have cleared up some thoughts in my head and I appreciate your help.
Anytime... you know that man
One thing... loose the switch
Reconfigure using a 24v coil relay DPDT Normally ON of 60-whatever Amp Rate (or multiple in parallel)...
Rewire so your 2 banks of 36v fat packs are connected in series using these DPDT NO position.. so 74v becomes the norm (since your not interested in switching back and forth) - the relay will handle the current load with little resistance so no worries there...
Wire it so that when the 42v charge supply is connected it energizes the DPDT relay and disconnects the Series Connection... while establishing the parallel connection between the 2 banks of 4Packs4Parallel...
This means it will auto switch to 36v mode for charging and then back to 74v mode when charge is complete or charger is removed...
It will also handle the discharge current in a small package and one where the power to engage the charge mode is handled via simply connecting the charger power
That may perhaps be the sweetest feature I've come up with for these yet...
I think I wil need to get some of these, they are what 2.3AH each pack? So I would need just 4 Packs for 40+ mi range @ 20mph and 20+ mi range @ 35-40 ish depending on sag.. What's the sag under load like on them? What are the C ratings (any ideas? - how many amps can each single tool pack deliver?)
I assume besides keeping it simple, you don't want to add balance lines because don't these carry some form of replacement warranty so long as they are not modified / opened?
That would be a big plus towards me picking some up for the customers ride... just have to use whatever type of tools they normally use
Hope I've been helpful and not just more confusing and thanks in advance for the feedback!
-Mike
