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Discussion Starter #1 (Edited)
Hello and sorry to start yet another BMS thread.

I have 30 EVpower cell modules that I was about to install on TS lfp260ah cells. Recently EVDL list bot reported some failures of these boards, possibly to incorrect install.

Can others report in with success/failure stories for this system? I believe BMS is a good thing, but NOT if it is more likely to cause cell death than running free.

I have an Elcon charger that should protect the pack from excessive high voltage even if the shunts and bms charger control switch fail. (at least I hope so) :eek:

However, a shunt failing open and draining a cell is a BIG CONCERN since these are $300 cells and replacements might be impossible to find. :eek::eek:

Also worth noting is this car will be used by someone who does NOT want to constantly check cell voltages, so I need some kind of fail safe system which is why I chose the cell modules in the first place.

Please advise.
Thanks

p.s. am I heading down the slippery slope to bottom balancing and no bms? argh! ~< :|
 

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Discussion Starter #3 (Edited)
That's not the slippery slope, it's the smart way to go. Just be careful when calculating the max charge voltage.
Not THAT smart. Actually, I would call it "dumb" in the sense of smart-bomb vs dumb-bomb. You wouldn't remove the thermostat on an ICE and hope it was running the correct temp. Electronics have proven themselves very reliable IF properly designed, manufactured, and installed. Thats a big IF. :eek:

If I bottom balance and cell capacities vary by much then the weaker ones will be going to higher voltages, further reducing their capacity and making the problem worse over time. The only solution is to reduce the max charge voltage, which is pre-set and unadjustable at 3.65v on this charger.

Since the charger is stuck at a pretty high voltage, I might be better off top-balancing and not running the batts below 70% if running without bms. yes?

I am still waiting for stories of success/failure using this BMS. Has anyone put on 50,000+ miles without a BMS?
 

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The only solution is to reduce the max charge voltage, which is pre-set and unadjustable at 3.65v on this charger.
You have options regarding final output voltage for your Elcon charger. :)
 

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Discussion Starter #5
You have options regarding final output voltage for your Elcon charger. :)
Is the method of adjustment to send it off to be reprogrammed? From what I gather, the factory installed several charge "profiles" indicated by the number of blinks on startup. Selecting a different profile just changes the amp-rate, not the voltage. To do that I have to get a new set of profiles?

I should mention I have the "Chinoz" stickered Elcon. Later they went by Chennic. It has the tiny 5v wire which activates it that nobody has heard of. I haven't quite figured out how to get that switched with the evpower bms. I can use the aux bat and drop 12v to 6v, but that will drain the 12v while charging and I don't necessarily want the dc-dc on all the time, so I may need a small 12v charger to keep the aux bat happy.

I must say that I am a bit skeptical of bottom balancing since it allows variation at "average" full charge, a place you are going to be A LOT. Top balancing creates issues at full discharge, which can be easily avoided by not running the car down. Am I not getting something?

Also, damage from over-charging seems worse (swelling and venting) than pulling a cell too low from which they seem better able to recover. (from what I have heard)

Cheers
 

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Not THAT smart. Actually, I would call it "dumb" in the sense of smart-bomb vs dumb-bomb. You wouldn't remove the thermostat on an ICE and hope it was running the correct temp. Electronics have proven themselves very reliable IF properly designed, manufactured, and installed. Thats a big IF. :eek:
I don't believe they have. I think they're designed for 2-5 year lifespan and need to be greatly overdesigned to last the lifetime of the vehicle, which makes them really expensive. The batteries can last 10 years. We have BMS's failing all over the place right now. Do you really believe a shunting resistor will last 10 years and over 3000 charges?

If I bottom balance and cell capacities vary by much then the weaker ones will be going to higher voltages, further reducing their capacity and making the problem worse over time.
With batteries which have over 3000 cycle life, the change in capacity between two batteries which finish at 3.65 and 3.60 will be negligible for 1500+ cycles. If you have a battery packs getting 100 miles range, then those batteries will stay together in capacity for 150000 miles. And even then, all you'd have to do is change the lowest capacity battery, costing you $250 bucks?
 

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Discussion Starter #7
but there is no DATA... only probably..

It is no coincidence that the battery companies who make and test these batteries recommend bms or install them at the factory. They should know.

I AGREE wholeheartedly that the current crop of bms has me concerned enough to question the installation.

However, when was the last time you had a blinker circuit go bad? Or a failed relay? Or even a blown fuse? Only bulbs and sensors subjected to extremes of heat and gunk go bad these days. Auto electronics are generally VERY reliable. My Subaru has 200,000+ miles with no issues. Only failures to date are water pump and battery cable. I last changed the oil 45,000 miles ago. :eek::eek:

This guy has 16,000 miles using the same TS lfp260ah batts and the EVpower bms. He does report 2 board failures, but only after several charger failures and batt reconfiguring. These are supposedly very sensitive during install, so that is very likely the cause of failure, not random failure.
http://www.evalbum.com/2314
He has more miles than anybody I have found, but many do not list miles.
 

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but there is no DATA... only probably..

It is no coincidence that the battery companies who make and test these batteries recommend bms or install them at the factory. They should know.
That's so they have something else to blame when a battery fails.

I AGREE wholeheartedly that the current crop of bms has me concerned enough to question the installation.

However, when was the last time you had a blinker circuit go bad? Or a failed relay? Or even a blown fuse? Only bulbs and sensors subjected to extremes of heat and gunk go bad these days.
Seriously? My house heating circuit died about a month ago, had to spend $150 to change it (it was a 24vac relay). Two of my friends just complained their computers died, and I built one of those so I know it had a good air circulation. And if you don't think the battery BMS's will get gunk and will be exposed to high temps (especially the shunting resistor) after 10 years of driving, then I guess you would put your batteries in boxes with no ventilation or cooling.

Auto electronics are generally VERY reliable. My Subaru has 200,000+ miles with no issues. Only failures to date are water pump and battery cable. I last changed the oil 45,000 miles ago. :eek::eek:
I'm going to stop then...
 

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Discussion Starter #9
That's so they have something else to blame when a battery fails.
except that they are still to blame since it is their bms, so obviously they think the risk of failure using bms is less than without. Everything is an odds calculation.


Seriously? My house heating circuit died about a month ago, had to spend $150 to change it (it was a 24vac relay).
Right. Everything fails (it's called entropy). Again, it's a numbers game. Let's compare the likelihood of a house to burn down from a wood stove vs. an electronically controlled heater. I think you will agree the electronics are MUCH more reliable than humans.


Please don't tell me you believe the 3k oil change propaganda from oil companies, but are skeptical of BMS companies? Consumer reports did NYC taxi tests and could find no difference at the end of service life when the engines were broken down and measured for wear. Long-haul trucks have proven over 1,000,000 miles with NO OIL CHANGES. It is estimated that 2-3 BILLION gallons of oil could be saved every year on unnecessary changes (if you went to changing it once a year).

Read here from real truckers discussing how 100,000 mile changes are CONSERVATIVE. Just an example, there is a ton of info out there on this.
http://www.thetruckersreport.com/tr...n-wheelers/87034-100-000-mile-oil-change.html

Education has no end-game
 

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Some of us are suspicious of running sealed auto engines as if there were 1950 Olds V8s with the air cleaner off & open crankcase breathers being driven by me in a dusty tank training course in Metuchen, New Jersey. :eek:

Damm. That car was TOUGH !!! Did it 1 a week. I was bad.

I have gone 15,000 miles between every oil change for ??? 25 years. No power loss or oil smoke & good compression. All my cars are bought new & NEVER go to a car dealer. Maybe that is why they never have any problems ??:)
 

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Is the method of adjustment to send it off to be reprogrammed? From what I gather, the factory installed several charge "profiles" indicated by the number of blinks on startup. Selecting a different profile just changes the amp-rate, not the voltage. To do that I have to get a new set of profiles?
Here is what I did.... I had to get my 6kw 192 volt lead-acid Elcon re-programmed for lifepo. I also wanted final voltage output adjustability. So, I have Greg setting my curve # 5 to the voltage I want (3.5 * 65 = 227.5) Curve 4 will be 1 cell less (-3.5v) Curve 6 will be 1 cell count more (+3.5v). . . and so on. 1 - 10.
This does two things for you ... (well one thing for two purposes... :)) It allows me to add a cell or two, or to adjust if I loose one... with no major issues.
It also allows me to adjust my final voltage. I can keep my 65 cells and pick curve # 4 and now I am charging to 3.44 vpc.. . as an example.

There is also a mod done by one user on how to mod the charger to get a bit of fine tune adjustment. I have it saved somewhere if you want it.
I should mention I have the "Chinoz" stickered Elcon. Later they went by Chennic. It has the tiny 5v wire which activates it that nobody has heard of. I haven't quite figured out how to get that switched with the evpower bms. I can use the aux bat and drop 12v to 6v, but that will drain the 12v while charging and I don't necessarily want the dc-dc on all the time, so I may need a small 12v charger to keep the aux bat happy.
It's only 10ma... so, as long as you aren't leaving it for days on end... not a big deal.
I must say that I am a bit skeptical of bottom balancing since it allows variation at "average" full charge, a place you are going to be A LOT. Top balancing creates issues at full discharge, which can be easily avoided by not running the car down. Am I not getting something?

Also, damage from over-charging seems worse (swelling and venting) than pulling a cell too low from which they seem better able to recover. (from what I have heard)

Cheers
The rest I'm not touching...been hashed every which way so far... :p
 

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Discussion Starter #13
Or just do what I did. Add an extra cell or two. I had my Zivan programmed for 19 cells for 3.65vpc and then I installed 20 cells so my ending voltage is 3.485vpc (I adjusted the calibration pot up a little).
I wish that was possible, but I think the cells I have are pretty much it. I am not sure there are many 260ah in the country. I have only seen them in one other build, and nobody seems to carry anything bigger than the 200ah.
 

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Not nice to add or replace old cells with new ones.

The peak voltages of each old & new cell are different. That should require the individual cell charger type to prevent over & under charging the pack. You will get a desired final voltage that you wanted.

But the price paid by a... constant series current...charger can be over charging some cells & undercharging others.

When you have different fully charged, cell voltages, you should be using a charger that can ....equalize every cell....even if some are at .250 volts lower than the rest.

Your call.
 

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Discussion Starter #15
1. Right now I have a nicely matched set of 30 cells. I want to keep them healthy so they stay that way.

2. Thus the reason for the shunts on each cell to keep everything together. The shunts should allow for the inclusion of new cells, provided they are brought to a similar state of charge as the rest of the pack before inclusion.

3. If a shunt fails to pass current, that is really no different than somebody who has no bms. The charger should shut off before any cell reaches 4.25v as they should be pretty balanced and reach the top around the same time. The real concern is a shunt sticking in the passing current phase and draining the cell once the charger is shut off. THAT would kill the cell for sure.

The whole point of this thread is to find out if that is a common occurance, but so far I have a EVpower real-world dataset of 0. Not exactly a good place to make a statistical call.
 

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You have a 30 cell pack, right? I put a 40 cell pack with the EVworks regs in the Datsun and am now putting 32 in my EV Buggy. If your cells are at the same state of charge you can charge to 3.65vpc using the EVworks regs. Watch that first charge because you need to be there to shut it off if any cell's voltage goes to high (that would mean they are not will matched in state of charge.)

One option for adding a cell is to parallel a couple of cells that add up to slightly more than 260 amp hours for that extra cell. With the extra capacity take about a third of it off the top and the rest is extra padding at the bottom. Example: if your 2 new cells add up to 290 amp hours you would fully charge them, paralleled and treated as a single cell, then discharge it by 10 amp hours. Fully charge your 30 cell car pack and then add the extra "cell" in series with the pack. It should comfortably stay in the middle of its range for the entire capacity of the rest of the pack. The charger should then be taking the cells to about 3.53 volts at the end of charge.
 

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Can others report in with success/failure stories for this system?
You might check with Willie McKemmie (sp?) on EVDL, he has been using them for a couple years I think. Also might send Dave Kois at currenttechev an email, since he used them on his earlier conversions for a while - should be 4 or 5 years or so on them now. Supposed to be pretty good. Overall design is similar to the minibms - I think Dimitri said that their design discussion on an aussie forum is where he got his inspiration. But the devil is in the details, I don't know how they differ and what issues that might leave them exposed to. I believe Rod Dilks was the, or one of the, designers, so might email him at evpower also. Seems like a straight-up guy, and a LOT more experienced than most of the talking heads here.
 

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They where installed in May of 2010, so they have been powered up for 9 months now. For the most part, the old Datsun only made the car show and cruise circuit this summer, so perhaps 200 miles and 20 cycles. None of the cycles have been deep, none of the charges have taken the average cell voltage over 3.7 volts (over 148 volts for the 40 cell pack.) The EVworks modules where most carefully installed so none where ever dinged with high voltage or reverse connection. None have failed or shown any signs of problems. They seem to be very consistent in how little current they draw with the pack sitting there. The pack consistently has all the cells within 0.01 volt of each other. Even with sitting over the winter this is still true (all 40 read 3.32 volts.)

The factory paint '66 Datsun attracted some collector attention and I couldn't really enjoy putting working miles on a car that was so hard to get parts for. The new owner will be picking up the Datsun, less the EV parts, this Saturday. 32 of the 40 have been installed in my Buggy. I did enjoy blasting the pack around with up to 5C discharges last summer and fall and will continue my abuse with abandon in the buggy next spring.
 
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