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Re: Another EV bike :)

Posted: Wed Nov 05, 2014 11:45 am
by ChrisBarron
Haven't had enough time to spend on this project recently but back on track now (Was having too much fun riding my other bike, FJ1100, while the warmer weather lasted :) )

I've had a few problems with the cell voltage monitors. Each one consists of a microcontroller, daisychained via their own serial port. Sometimes when a relay dropped out on the bike some noise would cause the micro's to crash and require rebooting, which they do automatically, but it isn't reliable.

Yesterday I got finished testing the new configuration, which has a lot of noise suppression added to each monitor and they work faultlessly now, regardless of how much noise is coming from relays and the main controller.

The next step is to make up a set of monitors for the whole pack, install them and then clad the battery box for protection.

Re: Another EV bike :)

Posted: Sun Jan 18, 2015 7:47 pm
by ChrisBarron
I pulled the battery pack from the bike and decided the long messy balancer/monitor wires needed tidying up (The ones terminated with green plugs....)
BalWireMess.JPG (83.48 KiB) Viewed 18593 times

after tidying....
BalWireDone.JPG (93.63 KiB) Viewed 18593 times

I also added 10A fuses at the pack end of each balancer wire...
BALWIREFIX.JPG (194.08 KiB) Viewed 18593 times

The cell monitors have been running for 6 weeks, hooked up to a pack of 20 x 18650 cells in series, emulating the real pack's voltage taps. The voltage of the cells has hardly changed in 6 weeks, proving that the monitors draw very little current.

I'm going to look at cladding the pack next, once it is back on the bike

Re: 18650 multi parallel packs

Posted: Thu Feb 12, 2015 11:43 pm
by nigel.tegg
Hi Chris! More power to your batteries! I was considering one of these as a replacement battery for my ZEV 7100 that I'm sure heard of. I bought it 2 years ago with a fairly old (maybe 3 years without being charged) I replaced 4 cells, (3.2V 40Ah LiFeYPO4) it now needs at least 2-4 more, so time to replace the whole battery, probably. It is possible to shoehorn in 60Ah cells, with some mods to the box and frame.
I considered doing something similar to you, probably with new 3-3.4Ah 18650 cells, with are about £4 each and buying a custom 26-28p BMS for the correct chemistry. it's 7kW cont. 14kW peak
I also have the advantage of being a professional Electronics engineer (not hobbyist) and have work on EV batteries before. Namely, the TATA Indica Vista EV, 350V 200A car.
Also, a friend is a major Sinclair C5 customiser, and also want to do a 26-9V Lithium pack for his footwells. (about 40Ah)

Kind Regards, Nigel.

Re: Another EV bike :)

Posted: Fri Feb 13, 2015 9:07 am
by ChrisBarron
That's all very interesting Nigel :)

I think that I, like a lot of others, are banking (or even hoping) that the price of 18650's come down a little bit more. Of course, while ever they stay in high demand the price will stay healthy until production volume easily overtakes demand.

There's plenty of talk of a gigafactory (a new term for me too !) in the US taking in raw lithium ores at one end and producing vast numbers of 18650 cells at the other end. That should bring the price point down for sure !

The ZEV scooter looks like fun. The scooter design presents a useful form factor well suited to electric drive, and particularly with that rear hub motor. Makes me think about a DIY version of the Vectrix, using something like a Suzuki Burgman as the starting point.

I've been spending a lot of time recently fettling my FJ1100, and even got out on a great ride last Saturday to the Rest and Be Thankful in Argyll, 220 miles in 5 hours. And really had to fight to get back on to the electric bike project to do more work on the batteries. This is the year I finish it !

I've decided to make a 'smart master' controller for the cell monitors. On the test bed now are the 20 cell monitors hooked up to a string of 20 cells connected in series. Each monitor is powered by the cell it is connected to. Communicating with them is a PIC 18f25k22 which is reading the cell voltages a couple of times each second. This controller takes the raw A/D from each monitor and stores it, adds a calibration value to it, and if required converts it to an ascii voltage reading. It is running to an accuracy of about 5mV at the moment.

My idea is to make this master controller switch outputs to relays and send alarm signals, through both IO pins and over a serial interface. For example one output will always be high if every cell voltage is within safe limits, and it then goes low if there is an over/undervoltage condition. I intend to use this to control a charge relay and provide overcharge protection by shutting off the charge voltage via a relay. A similar thing can happen when one cell voltage drops below a preset minimum, to be used as an input to a power limiter or speed controller inhibitor.

There would not need to be any other hardware for the battery pack if I do this. However, I am using the second serial port of the smart master to return cell voltages, and to return the total pack voltage, so a small display can easily be added. This could also give a rough idea of how much energy is left, coupling it with an inline shunt could give energy useage measurements too.

Right now though my focus is on the pack protection function and once that is working as expected I can get the batteries in the bike and work towards getting it road legal again. I can add the other functions at a later date


Re: Another EV bike :)

Posted: Fri Feb 13, 2015 3:54 pm
by nigel.tegg
I guess that 220miles in 5 hours wasn't on an Electric bike!? (44mph av.) A ZEV LRC11 will do that of the shelf ( I guess you looked at it on their website. I speak to the owner/designer Darus Zehrbach occasionally. The main problem is the price of replacement cells. There is a new site (1 year maybe) in Poland, that are considerable cheaper than the Czech
or I'd recommend for your larger bikes, on an 84-96V system like the larger ZEV's use (26-28 cells) you can buy dedicated BMS's for these have a look at and you'll see the cells ZEV use in their new bikes (4 bolt terminal, doesn't come loose) and the exact same charger I have for my ZEV. Darus doesn't know the company, but they obviously buy similar stuff to him.
Regards, Nigel

Re: Another EV bike :)

Posted: Fri Feb 13, 2015 5:14 pm
by ChrisBarron
I've seen some of that gear before, but it's still good to remember it's there

I was toying with the idea of making a buddy pack from the newer grey CALB cells, with higher 2C continuous current rating, but found enough 18650's in the end, so I made a smaller Headway buddy pack.