Removable Cell Battery Packs

I'm pretty certain that the spring contacts in this battery holder will glow, soften, and loose their shape at 34 amps! The plastic will also melt.

A few years back, a fellow coworker made an electric bike with D Ni-Cads. I believe he used aluminum tubes (10-12 batteries long), thick copper contacts, and some heavy duty springs. Due to the large copper contacts and stout springs, contact heating was minimal. The aluminum tubes that held the cells also helped with heat dissipation. I think a thin Kapton sleeve was used to prevent any shorts to the aluminum. I didn't see the finished bike, so I don't know how easy single cell replacement was for his design.

Good luck with the NiMH design.

These are standard domestic D-cell battery holders and won't handle anywhere near 34A. I have melted the plastic on these with much less current passing thru the integral metal interconnections (although the weakest part is the thin insulated wiring which will fail with even less current).

For an application like yours I doubt you will find D-cell holders rated for 34A, mainly because D-cell batteries are not rated for powering a 34A load. For example, D-Cell NiMH batteries are rated for a discharge of between 2C up to a max momentary 4C (C being the Ah capacity). Additionally 20 x D-Cell NiMH batteries connected in series are going to give you a total internal resistance of about 0.4 ohms or more alone (not even taking into account the spring contact resistances) which is going to waste a lot of the battery power by converting it to heat.

I don't recommend D-Cell batteries for this application.

Hi everyone. I posted my electric bike project here a while ago, and I have since seen a failure of lead-acid battery technology. Wasn't a big surprise, but it won't support the deep discharging and normal charging cycles that the application requires. I routinely discharge the batteries to about 25.1 total voltage (2 12v 18ah batteries in series), and charge it typically to 27.4v.

I don't remember if you were using sealed or vented lead acid batteries. Sealed (maintenance free) lead acid batteries should be fine for this deep discharge application as long as you only discharge them to a minimum of 10V each (say 10.5V to be safe). They will work and last better and cost less than D-cells!

Did you over discharge or improperly charge them? If you used a standard car battery charger instead of a smart sealed lead acid battery charger that would explain why they died so quickly and unexpectedly.

Can you provide more information please.

The 34 amps would be a very maximum spike of the power I'd use. Typically the bicycle draws from 8-18 amps conservatively. I am going to reduce the motor gearing more and hopefully reduce that a bit more. The NiMH D cells I am considering are 10000mAh capacity, so 2c would be 20 amps. In normal working conditions this would pass your test for continuous discharge current...with an occasional spike of up to 30 amps.

Here is the link to the lot of D-cells I want to buy (pretty good price I thought...) : http://www.all-battery.com/20pcsofdsize10000mahhighcapacityhighratenimhrechargeablebatteries.aspx

I have discarded the idea of using those plastic battery holders since they are too wimpy. I like the other fellow's idea of using aluminum tubes...that would also help with the heat dissipation. We'll see what develops...but I would like to talk a bit more about this before I go and buy a bunch of NiMH cells.

I am currently using two 18000mAh 12v SLA batteries. Their designation is UB12180. The charger I am using was advertised as a 1.5 amp lead-acid battery charger at 24 nominal volts. Its one of those ones that plugs into an XLR port, so I designed the bike to take it. What type of charger should I use? A float charger? I think I'm going to ask down at the batteries plus nearby...

Also I keep having spokes snap on my back wheel...which is no good. The weight of the SLAs is just too much for it. I think my batteries might be ok though...perhaps they just need a service charge.

Snapping spokes is a sign you need something stronger. If I were snapping spokes, I'd also start to be concerned about how strong the frame is.

I'd personally stick with SLA batteries, but the NiMH option seems to work on paper. To get maximum capacity AND life from any batteries, you need a smart charger designed to work with the battery chemistry you are using. There are specific temperature compensated voltage and current limits which will maximize your battery performance.

http://www.batteryuniversity.com

is a good basic starting point for learning about different battery technologies.

I am not sure what my charger is...whether it is a smart charger ...or a trickle charger with a voltmeter designed to cut it off when it gets to the proper voltage. Its just a "class II 1.5amp charger" that I bought off ebay.

There have been 2 spokes that snapped. First time I had 26.4 lbs of batteries hanging off one side of the bike...side loading was the cause I think that time. This most recent one was because the drive chain was thrown when I shifted to my lowest gear...and threw itself right into the spokes on the wheel.

GA.

Lot of good stuff.

I had a look on the internet for some reviews of the Tenergy D-Cells you describe and found these examples (there are more, try a google search of Tenergy D cell).

http://visforvoltage.org/forum/2475-tenergy-batteries

http://www.productwiki.com/tenergy-aa-nimh-batteries/

I would say you get what you paid for (ie- there is a reason they are cheap). Technical details from Tenergy are seriously lacking (or in some cases actually misleading).

http://www.tenergybattery.com/index.php?option=com_virtuemart&page=shop.product_details&flypage=&category_id=1&product_id=393&Itemid=1

I would suggest sticking with your sealed lead acid batteries due to my comments above. Give them another go before you switch to the D cells and fork out all that money for what appears to be an inferior product. Additionally you WILL need a special charger specifically designed for D-Cell NiMH batteries, and it will almost certainly be the type that individually charges up to about 4 at a time (meaning long recharge time while you swap out 4 sets of 4 batteries or 4 battery chargers required).

http://www.tenergybattery.com/index.php?page=shop.product_details&flypage=shop.flypage&product_id=63&category_id=15&manufacturer_id=0&option=com_virtuemart&Itemid=27

The charger I am using was advertised as a 1.5 amp lead-acid battery charger at 24 nominal volts.

Is it designed for SEALED lead acid batteries or standard vented car batteries. The documentation will mention sealed lead acid batteries if it is designed for it. If you don't know do you have an internet link or brand name and model so we can advise you if it is suitable. A car battery charger which isn't designed to charge sealed lead acid batterys will overcharge, overheat and kill the batteries rather quuickly (especially if left connected when the battery is fully charged).

I think I'm going to ask down at the batteries plus nearby...

Yes they should know.

Thanks for checking those out. I thought it was odd that under "tech specs" they didn't have a discharge characteristics diagram of some kind. I do know about the fact that SLAs will provide less capacity at a shorter discharge. Doesn't the SLA chemistry tend to dislike full discharge and recharging?

Charger brand and model #: QILI Power, Model#QL=09005-B2401500H. It doesn't specifically mention SLA on the sticker label...so maybe I have the wrong type of charger. I think it is the "burp" charger that someone else mentioned above...it is NOT a trickle charger.

The weight is my main concern when it comes to keeping the SLA chemistry aboard my bike...it barely stands up on its own...is very difficult to lift from place to place...and is just overall ridiculous to maneuver in and out of tight areas in my house where I keep it. I would really like to go NiMH...even despite the extra cost. Ideally I want to set up a series pack OR buy 2 battery packs that are 24v each and connect them in parallel with a voltage continuity monitoring system (to be built by me in my electrical fundamentals class this year!). One of the biggest issues related to the weight is the center of gravity is too high and too far back. I need to find a way to rearrange the batteries. Take a look at the photos below...

Depending on the geometry & your position a regular bike has 75% of the weight over the rear wheel.

Consider mounting the batteries on each side of the fork down towards the axle. This would improve the weight bias.

Never did quite catch how the free wheel, electric drive is set up, more pics please

You could use honeycomb drilled pvc to hold d cells, though Delmar's suggestion is a good one

Would stick to lead bats, just don't let them discharge so much. If it seems you have to, this is proof you underestimated your power needs. Use bigger and/or more. And another thing does your system involve power regen on deceleration? If not dont expect much on any type of batt a bike could carry. Concider it effective if you only have to use brakes when stopped

You might want to look at one of those small bike trailers as a location for the batteries. This will allow you to lower the center of gravity on the bike, making it easier to balance and more pleasant to ride. No point having an electric bike that is no fun to ride.

I am not going to comment about weight and snapping spokes, thats a different problem. Still important though!

But SLAs are not necessarily the right Lead Acid batteries to use, Leisure Lead Acid Batteries (which can also be bought in SLA form) can accept deep discharging without such problems.....they are a bit more expensive, but have far longer lives.....

Look here for example:-

http://www.tayna.co.uk/Leisure-Batteries-C45.html

When charging ANY 12 volt lead acid battery, do not gas the battery, which means keeping the voltage to 13.8 or less. A good intelligent charger is needed and it is best NOT to charge the batteries in series.....or parallel, but parallel is better than series.

Not fully charging voltage wise (staying with 13.8 or less) means that you can ignore temperature correction that a LA battery normally needs......if you were charging before and gassing or ignoring temperature as well as deep discharging, its no wonder the batts did not last long, it could actually be days instead of weeks under really bad usage.....

If you believe that you cannot gas a SLA, then you have not fully read up on Lead Acid batteries.....if you need some good links just ask.....

You should remember that ANY battery (of any type/chemical), each cell (even in a 12 volt battery) is an "individual" and it has different charging, discharging and capacity to the other ones.....that is why you should read the manufacturers instructions and do not "push the envelope".....staying within the envelope means that none of the cells get damaged.....

Those battery holders are not good enough, also such batteries must also not be deep discharged AND they need a really expensive charger, one that does single cells is best. Leave them alone and stay with Lead Acid is my personal tip.....

If you want to use D cells, use ones with tabs.......and thick copper connections......done properly, you can still replace them individually, but even that is not a good idea really. A new cell in an old set will usually take more with it......

Make sure that you get indication of when the battery is really empty, to prevent deep discharging.

Maybe you also need bigger batteries......

In my neighborhood I always see little kids riding around on battery powered Barbie cars and other four wheelers. These batteries must be relatively small and light, and the cars come with a matching charger. Most are 12 volt but a couple of battery packs could be wired in series. Might be a good and cheap source for your needs.

Saw come on eBay rated NP12-12 12V, 12Ah for around $40 each.

http://cgi.ebay.com/Lead-acid-YUASA-NP12-12-12V-12AH-rechargable-battery_W0QQitemZ110438333671QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item19b6a33ce7&_trksid=p3286.c0.m14

http://cgi.ebay.com/Power-Wheels-replacement-Battery-12-volt-NEW_W0QQitemZ200385202218QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item2ea7e3882a&_trksid=p3286.c0.m14'

Instead of lead acid or D cells, use Lithium Fe Mg batteries. Li Ion or Li poly would work very well, but they are finicky to charge and can easily be damaged if deep drained ( I've had a couple of LiPo batteries catch fire on me ). I have found an excellent source of these batteries in china Here is the info NOTE: I do not work, nor have stock in this company, but I have purchased from them before. ) They have cells ranging from 3.2V @ 10AH up to 3.2V @ 1000Amps ( think that will be enough power for your bike (:>) ?

Advanced Battery Factory(Sino-America Joint Venture)

Add: JinXiu JiangNan, Shen Zhen, Guang Dong Province, China.

Phone: 0086-138-236-53608( 24 hours a day, 365 days a year) , 0086-755-8147-6290

FAX: 00 86-755-2806-9141

Website: www.splendidbattery.com

e-mail: allbattery@21cn.net

Lead-Acid does not like deep discharges and you will be limited to so many cycles. I try not to deep discharge and my UPS is lasting a very long time which uses a gel type. Maybe use two of them and switch over to the fresh one before total discharge?