NiMH options?

Hey folks, I am pretty new to EV bikes, I'm putting together a nice commuter/cruiser with a 750W goldenmotor rear hub motor and cruise controller currently. I'm going to use it to commute to work which is 7.8 miles away, I can charge up at work when I get here, I doubt I'll be running pure EV, I want to pedal as well (help me get in shape and less battery run down).

I had planned on making my own pack using 32 D cells in series at 10Ah to give me about 380 watt hours give or take, however now I am doing more research it seems that most manufacturers grossly (lie?) overstate their amp hours on these D cells, particularly tenergy. I did find another cost effective brand out there "powerizer" but I can find little information on them?

I would prefer to stick with nimh chemistry as its robust and long lasting, does anyone know any good websites that actually test batteries and measure the real amp hours? I can't find any that do this, if not I might end up buying some single sample and making my own rig at home.
Any good websites for buying large quantities of nimh cells, I've found some online but not a loads.

I've even considered using AA nimh cells as some of these have solid 2.3Ah ratings which actually match the manufacturers specs. (there seems to be a drive for high quality AA nimh cells for digital cameras)

thanks!

I don't think that you will have enough battery for that motor. Battery sag will limit your range causing your controller to cut out because of low voltage.

But I could be wrong, I have before .

Nick

Well thats why I was going to use 32 cells, giving me nominally 38.4 volts, at the end the nimh's should be around 0.9-1 volt so about 28.8-32 volts.

Unless I'm miscalculating?

Had a quick peek at ebike.ca to see what sizes of NiMH packs Justin has:
http://www.ebike.ca/store/store_batteries.php

All the NiMH product listed as Discontinued or Clearance... Hmmm... Would be nice to know why that is.

bart_dood said:

Hey folks, I am pretty new to EV bikes, I'm putting together a nice commuter/cruiser with a 750W goldenmotor rear hub motor and cruise controller currently. I'm going to use it to commute to work which is 7.8 miles away, I can charge up at work when I get here, I doubt I'll be running pure EV, I want to pedal as well (help me get in shape and less battery run down).

I had planned on making my own pack using 32 D cells in series at 10Ah to give me about 380 watt hours give or take, however now I am doing more research it seems that most manufacturers grossly (lie?) overstate their amp hours on these D cells, particularly tenergy. I did find another cost effective brand out there "powerizer" but I can find little information on them?

I would prefer to stick with nimh chemistry as its robust and long lasting, does anyone know any good websites that actually test batteries and measure the real amp hours? I can't find any that do this, if not I might end up buying some single sample and making my own rig at home.
Any good websites for buying large quantities of nimh cells, I've found some online but not a loads.

I've even considered using AA nimh cells as some of these have solid 2.3Ah ratings which actually match the manufacturers specs. (there seems to be a drive for high quality AA nimh cells for digital cameras)



thanks!

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A couple of guys on pedelecs.co.uk built AA Nimhs into packs. Not bad, but the high internal resistance of so many cells limited performance. They just aren't designed to be built up like that.

I'd just get a couple of Nicad pack from ebikes.ca. 288Wh should easily get you to work. Plus you get a pack from a trusted supplier. For longer ranges, there's Ping.

<snip>
thanks!

[/quote]
A couple of guys on pedelecs.co.uk built AA Nimhs into packs. Not bad, but the high internal resistance of so many cells limited performance. They just aren't designed to be built up like that.

I'd just get a couple of Nicad pack from ebikes.ca. 288Wh should easily get you to work. Plus you get a pack from a trusted supplier. For longer ranges, there's Ping.[/quote]

Well if I did use AA batteries, I use 3-4 in parallel and then place them in series, so their internal resistance would be 1/3 to 1/4 of a single cell.
Looking around I've noticed NiZn AA cells are coming on the market and are affordable, might be interesting to delve into this new chemisty.

bart_dood ...

Welcome to the forum.

Don't attempt to build your own NiMH or NiCD pack until you understand the thermal characteristics of the chemistry.
Otherwise you are bound for disaster.

I run NiMH all the time and love them.
I also use cheap Powerizer and Tenergy and they work fine.
I build my own packs and do break some rules yet they work.

BUT .....

1) Volts x Amps = Watts
I run 72V battery systems (60 cells in series) with a 72V controller.
At 72V I need half the amps than running a 36V system.
72V also means more speed (25-30 MPH).
NiMH (and NiCD) batteries will get hot as you draw more amps.

2) D-size takes heat better than C-size, C-size takes heat better than subC-size.
BUT ... You can NEVER EVER run cells in parallel within a single "pack" of cells.
A pack of cells must ALWAYS be in series.

(You can run packs in parallel but you can never charge cells in parallel).

3) Cell packs should generally be made in groups of 10.
Each 10-cell string is 12V nominal (and up to 15V while max charging).
So a 30-cell (series) pack is 36V nominal.
A 40 cell pack is 48V nominal.
A 60 cell pack is 72V nominal.

4) Charging ... (-) dV/dt AND (+) DT/dt
Ni cells need a minimum of 1.41 V/cell for charging.
As they reach full charge (over time t) their Voltage (V) climbs and the Temperature (T) increases.
But at FULL charge their V drops a little and the Temperature goes up quickly.
I ALWAYS install a max Temp sensor in my packs to terminate all charging current above 50 deg C (122 deg F).

BUT I am sneaky ...
I use a cheap 1.8A 36V SLA charger to charge my 30 cell packs with a separate charge lead connected to the 50C sensor.
The temp sensor is embedded in the "center of mass" of the pack,
My packs are nice and warm when fully charged (so I then let them cool down before use).

5) AHr Capacity is measured at the "C" rate / 20
A 10 AHr D cell is rated for 500ma over 20 hours.
But I usually pull 3-5 x the C rate.
I am lucky to get even 70% of the AHr C rate at 1 C. At 4C maybe 60% and they GET hot while being used.
But Hell ... I don't care ... the cells are cheap and packs are easy to build.

If you want to see some CHEAP NiMH builds I'll post the pics.

I also have an old thread on the subject ...
http://endless-sphere.com/forums/viewtopic.php?f=14&t=5316&start=0

As already mentioned, running a 750watt motor on 36v NIMH is very difficult; that means over 20amps continous --and few reasonably priced NIMH's can do this. 10-11 amps at 72 volts is much easier, or go 48volts & try for 15 amps, or use two packs in parallel.

the internal resistance of reasonably priced NIMH packs makes for lots of heat at 20 amps and shortens the life of the pack.

With NIMH and hgher power motors, Higher voltage is the key.

BEST

D

deardancer3 said:

As already mentioned, running a 750watt motor on 36v NIMH is very difficult; that means over 20amps continous --and few reasonably priced NIMH's can do this. 10-11 amps at 72 volts is much easier, or go 48volts & try for 15 amps, or use two packs in parallel.

the internal resistance of reasonably priced NIMH packs makes for lots of heat at 20 amps and shortens the life of the pack.

With NIMH and hgher power motors, Higher voltage is the key.

BEST

D

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Well I don't plan on running 100% EV if you read my first post, most of the time I'll be running around 10Ah, 20Ah bursts would be for a few seconds on occasion. Doesn't running the motor way above its rated voltage cause problems?

I can vouch for the increased range and lower AH consumption at higher voltages. Im currently using 96v (84v Nominal) Yeah you could draw the full amount you controller can put out at 72v (35A in my case) but yo realize you dont need to all the time. You back off the throttle alot. Its safer for your and the pack. NIMH is one of those tricky technologies. The higher C rate you pull from them the worst they sag and perform. I almost compare them to SLA I have some Sub C Tenergy packs that are grossly overated in capacity and output. I get about 60-65% of the capacity out of my 12v 4200mah Tenergy Sub C packs. (2.5 to 3AH). These packs are 10C rated but only can produce about 3C without voltage sag. I put 4 in parallel and use it as a booster pack. 12v 12AH (Real Capacity) Im only drawing less than 10A from each in parallel. They stay in the 11+v range under load in parallel. I would only recommend NIMH for boosting applications not for full pack drop in. Unless you buy from Ebikes.CA then you get the good stuff that goes the true advertised distance.

icecube57 said:

I can vouch for the increased range and lower AH consumption at higher voltages. Im currently using 96v (84v Nominal) Yeah you could draw the full amount you controller can put out at 72v (35A in my case) but yo realize you dont need to all the time. You back off the throttle alot. Its safer for your and the pack. NIMH is one of those tricky technologies. The higher C rate you pull from them the worst they sag and perform. I almost compare them to SLA I have some Sub C Tenergy packs that are grossly overated in capacity and output. I get about 60-65% of the capacity out of my 12v 4200mah Tenergy Sub C packs. (2.5 to 3AH). These packs are 10C rated but only can produce about 3C without voltage sag. I put 4 in parallel and use it as a booster pack. 12v 12AH (Real Capacity) Im only drawing less than 10A from each in parallel. They stay in the 11+v range under load in parallel. I would only recommend NIMH for boosting applications not for full pack drop in. Unless you buy from Ebikes.CA then you get the good stuff that goes the true advertised distance.

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I was just worried about running too high a voltage on my motor, its a 36 volt unit and my controller is 36 volt too (goldenmotor cruise type). I will do some more searching on the forum etc on running higher than rated voltages.

The thing that draws me to nimh chemistry is its longevity. In hybrid cars nimh cells (D type) have been used in Honda insights since the year 2000, many of these cars are still using their original packs, even those that have had problems are usually confined to a few bad cells in the pack and can be switched out. So these things are probably good for a 9 year service, perhaps even 10 years.
The hybrid D cells are slightly different from regular cells, they are about 6-6.5 amp hours but have thicker electrode designs which allow very high input/output current (100amp) so I don't expect regular cells to last quite as long as these specialised ones.

However, I decided I was going to tackle the thermal issue of nimh batteries with heatsinking aluminum tubes and also an active fan system to keep everything running cool. Especially during charging.

i think you are at the overanalyzing stage. if your controller is for 36V, then it has been set so the LVC will turn off the controller when the battery voltage drops to 31.5V. that's what that means.

the controllers have parts internally which will break down if the voltage is increased above their specs. like caps usually 63V, and the FETs are usually good up to 75V so you should have no problem running higher voltages through your motor.

depending on how high a voltage, you may have to add some resistance to the input power resistor which carries current to the voltage regulator so the regulator doesn't see too high a voltage, and if you go over 63V you need to swap out the 63V caps, but you should be able to use the controller up to 72V nominal with those fixes and 75V FETs.

when kuncle knuckels (methods started it, but he just is like everybodies favorite kunckle) talked about 1.41V he means that the cell is fully charged, 100% when it is at 1.41V, and the voltage drops then as you push more current into the cell, and then the temp rises rapidly because it is heating the cell rather than charging it. try to avoid long periods with the charging above 1.41V/cell.

bob mccree also has a famous build where he soldered the nicads, something which must be done with great care to avoid damaging the cells if they exceed even a low temp, so use really low temp lead/tin solder 60/40 or so.

build your battery to fit the charger since that is the limiting factor. 36V nominal or 48V nominal, or go straight to lifepo4 also. read more too.

BOL, dm

With the ebikes.ca nimh, comparing prices with lifepo4 might give you an idea why they might be selling slow. I still think the ebikes.ca nicad is still a good battery to buy, particularly with a recreational bike, as opposed to one that gets pounded to dust commuting a long distance. Nicad won't die from non use, and will still be good years from now if the bike is only used 30 times a year or so.

Consider the Toyota Prius battery module, which is also NiMH chemstry! Prismatic cell, not cylindrical. They have different charging & discharging characteristics. They work for me: see http://endless-sphere.com/forums/viewtopic.php?f=14&t=6726&start=75
I have been through SLA & LiFePo4. These are the most reliable, proven, easiest to consrtruct and cost-effective, IMHO. Also, I don't need a BMS or cell balancing.
--Tom_D

Tom_D said:

Consider the Toyota Prius battery module, which is also NiMH chemstry! Prismatic cell, not cylindrical. They have different charging & discharging characteristics. They work for me: see http://endless-sphere.com/forums/viewtopic.php?f=14&t=6726&start=75
I have been through SLA & LiFePo4. These are the most reliable, proven, easiest to consrtruct and cost-effective, IMHO. Also, I don't need a BMS or cell balancing.
--Tom_D

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I've taken a good look at them, I think it is a little more work to use them so at this point I've decided not to. I can see myself doing another electric project in the future and I think I'll be using them on that, they are cost effective and have some good advantages.