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Conundrum

Wed Dec 12 2012, 06:47PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Hi all, thought I'd post on the saga of the Powabyke.

So far I have a 2Ah 36V pack based on phosphates. but recently acquired some new old stock 5.2Ah 3.7V LiPo * 13 as the pack I built is using unsuitable cells with high internal resistance under load, dropping from 3.25 down to 2.7-2.5V on load with insufficient known good cells to substitute for further testing.

So far the plan is to have a pulse width controller to limit the voltage until the pack drops to 12.9V*3 (39V) so the bike controller works correctly then cut off at approx 3.1V/cell to give a good margin of safety.
The BMU boards are on order, and my lead acid charger can be adjusted to the required tolerance with boards having OCP and LVCO built in.

Should I be adding any other failsafes to this thing, over temperature might also be advisable
so the pack shuts down in the event of one or more cells getting over 40c.

Also on the modifications list:- a better clamping mechanism to hold the heavy pack in place.
I have a salvaged V2 lock which has the key and most of the mounting hardware needed and intend to add a push button servo lock/unlock to take the pack off for charging.

-A

Patrick

Wed Dec 12 2012, 07:53PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

I need pictures of your batteries, please !

TheAnomaly

Thu Dec 13 2012, 12:29AM

Registered Member #5620 Joined: Sat Jul 07 2012, 01:41AM
Location: Jacksonville Fl
Posts: 8

I think charge is an important thing to monitor.

teravolt

Thu Dec 13 2012, 05:22AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

fuses should be also included

teravolt

Thu Dec 13 2012, 05:28AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

fuses should be also included

nixie

Fri Dec 14 2012, 01:31PM

Registered Member #3908 Joined: Tue May 24 2011, 09:40PM
Location: Gilbert, Arizona USA
Posts: 68

HI, please be careful with LiPo.
Zippy, Turnigy, Thunderpower, and basically all of the other HK/China brands are intended for the hobby market. In the best of situations it's not uncommon for a materials defect or separator failure. Put a load of the them together and you can have a dangerous situation. They're so attractive because they pack a lot of energy in a small package.

LV (low voltage) cutoff at the cell level is critical. Never allow open cell discharged voltage to drop below 3v. HV (high voltage) cell limit to 4.2v max. Charging events are nearly always the result of one or more cells discharged below the minimum voltage on the previous run.
Even when you're careful, stuff happens. I had a 6P Turnigy hardpack ignite unexpectedly in my garage a year ago. It had been left in a metal storage container, with a partial charge.

I'm a ebike tinkerer as well. And I've resolved to stay with iron phosphate cells (A123) because they're a bit less dangerous, albeit much heavier.

The clowns over on endless sphere forum usually have a new thread weekly about someone's ebike lipo pack going up in flames.

Steve Conner

Fri Dec 14 2012, 02:51PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Will you still be able to get those, now that A123 Systems has gone bust?

nixie

Fri Dec 14 2012, 05:29PM

Registered Member #3908 Joined: Tue May 24 2011, 09:40PM
Location: Gilbert, Arizona USA
Posts: 68

Steve Conner wrote ...

Will you still be able to get those, now that A123 Systems has gone bust?

A123 products will likely resurface under another brand. Although they did produce the best product for a few years while others were racing to pinch their materials processes, or independently develop their own.

There certainly are plenty of A123 haters. Maybe it relates to the US government handout$. And it's unfortunate that a production process fault + a lot process identification error were enough to topple them (one of four parallel production lines produced defective material, while all four shared the same lot ID).

I had some skin in the game back in 2007 when I assembled a high performance electric sports car using 3360 of the A123 M1 cells in a series/parallel configuration.

There are 28 modules of 120 cells. Four 30 cell parallel clusters are arranged in series make up each module. The 23kwhr pack weighs 255kg.

A123cluster1

Amazing cell performance. Although the pack capacity has been reduced 15% on the five years since it was assembled. Cell impedance has risen by an average of 8%.
LiCo cells are typically beyond their useful life in the same time.

Steve Conner

Fri Dec 14 2012, 06:02PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Very impressive

, what sort of drive did you use? The AC-150? and what mileage did you do in those 5 years?

nixie

Sat Dec 15 2012, 04:36PM

Registered Member #3908 Joined: Tue May 24 2011, 09:40PM
Location: Gilbert, Arizona USA
Posts: 68

Steve Conner wrote ...

Very impressive

, what sort of drive did you use? The AC-150? and what mileage did you do in those 5 years?

Gosh, I'm very sorry to have hijacked conumdrum's ebike battery thread. One final reply to Steve and it's back to you

Yes, it is the AC-150 by AC Propulsion. Normal driving range was unknown, considering it was always driven like I'd stolen it. 0-60mph was a bit over 3sec. Usual scoots were <50 miles.
Sad, short story; I grew ill in 2011. The battery pack, and it's tech were sold to a company in the UK. And immediately fitted into a another of the same model kit car. The cyclic data on capacity and impedance come from feedback in it's second life.

I'm still involved with small scale pack engineering. Typically 48-72v, 10-20Ah with varying levels of monitoring or management.

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