Extending The Range Of An Electric Bike

Cruising around town on your electric bike is surely a good time…. unless your bike runs out of juice and you end up pedaling a heavy bike, battery, and motor back to your house. This unfortunate event happened to Troy just one too many times. The solution: to extend the range of his electric bike without making permanent modifications.

Troy admits his electric bike is on the lower side of the quality scale. On a good day he could get about 15 miles out of the bike before it required a recharge. He looked into getting more stock battery packs that he could charge and swap out mid-trip but the cost of these was prohibitive. To get the extra mileage, Troy decided on adding a couple of lead-acid batteries to the system.

The Curry-brand bike used a 24vdc battery. Troy happened to have two 12v batteries kicking around, which wired up in series would get him to his 24v goal. The new batteries are mounted on the bike’s cargo rack by way of some hardware store bracketry. The entire new ‘battery pack’ can be removed quickly by way of a few wing nuts.

Connecting the new batteries to the stock system go a little tricky and the stock battery pack did have to be modified slightly. The case was opened and leads were run from the positive and negative terminals to two new banana plugs mounted in the battery pack’s case. The leads from the new batteries plug right into the banana plugs on the stock battery pack. The new and old batteries are wired in parallel to keep the voltage at 24.

Troy found that he’s getting about twice the distance out of his new setup. Not to bad for a couple on-hand batteries and a few dollars in odds and ends.

19 thoughts on “Extending The Range Of An Electric Bike

  1. This is the 26″ E-Zip bike from what I can tell from walmart’s website. You can buy far higher capacity LifEpO4 batteries for it to dramatically extend the range, but those batteries are ungodly expensive, as in $1500 for only 20AH at 24V.

    What I wonder is does this bike type allow you to “help” by pedaling with the motor so you can significantly increase range and will it do regenerative braking down hills? I am guessing at the price point all that bike has is a motor and a power switch with some plastic bits to make it look like a saleable product.

    The other thing is that the same bike is selling for 2-3X the price elsewhere. So what are the parts they left out of the economy version at walmart and can you buy the missing bits to make a full ebike….

    1. Without looking at specs of the motor (call me lazy), I’d assume the motor could propel the bike faster than what an average rider could pedal. In order for the rider to assist the motor, s/he would have to actually work harder than the motor’s output. Another assumption is that any type of charging system for the battery is going to add undesired weight to these already small motors, decreasing efficiency. Of course, this is all theoretical.

          1. I would be quite surprised if the top speed of that bike were faster than you can pedal in the highest gear. Especially if you were going uphill when the motor would be bogging down and drawing more current.

        1. The output will only add up if your drive sprocket is traveling faster than your wheel because of the freewheel mechanism. If you are, say, coasting downhill while pedaling very slowly then the human input will not contribute any amount to the overall speed of the bike.

  2. I’d recommend building or buying a battery isolator for the system or at least keeping the paralleled sources separated when not in use. Otherwise one 24v source will leach from the other; usually the larger capacity bank will destroy the lower capacity bank.

    1. I’ve always heard this argument against parallel batteries but never got the reason. Batteries charge and discharge all the time (their function) so the current flows both directions. Provided max min voltages and temp limits are adhered to, what is the harm?

      1. 0.5V is a pretty big drop at these currents. Also, voltage drop increases with current, so you’d be lucky to get 0.5V. Instead of using a diode, a better solution is to use a FET + perfect diode controller.

    2. I’d also be curious for some backup on this, as I have also heard this before but it also doesn’t make any sense to me in theory… To me this is similar to having two capacitors in parallel, they will just balance out in voltage, and as long as you have somewhat similar cells, there would be not reason for one to ‘discharge’ the other. Even if one cell is newer, it will just try to hold a higher voltage longer, and I would assume a higher current draw would pull from the newer cell under load, essentially ‘balancing things out’ in the end. Maybe under high load if cells are mismatched you could throw voltages apart a bit for a short period because of discharge rates and how well the cells hold voltage as discharged, which might cause a bit of ‘one cell charging the other a bit until there is a balance again’ after unloading, but I don’t see any serious harm in that either….

    3. Parallel batteries = one bigger battery. Think about it down to microscopic level…

      The only way for problems to arise is if you connect/disconnect the parallel elements during the use, which is not the case here. In general parallel elements regulate themselves quite well, as lower capacity or older ones tend to have a higher internal resistance, thus will provide a smaller fraction of the current.

    4. During the boom car era I built competition sound-off cars in my day job. To accommodate the enormous amount of current we needed, we paralleled batteries. If the batteries were identical, they tended to last for a while ok but if we used one type of battery for the car and different ones for the audio, from time to time we would loose batteries. It was not uncommon to disconnect the audio battery bank and find that the front battery was completely shot.

      There’s probably lots of science behind it (differences in resistance/capacitance, ect…) but my theory is this:

      1) Different capacity batteries discharge at different rates and as a result one will leach from the other. I’m not sure which battery will survive but I suspect the lower cap battery would be the victim.

      2) Larger cap batteries take longer to charge but a single alternator/regulator is charging the whole bank so lower cap batteries get over charged, overheat and damage cells. Not a problem on the bike if cells are charged separately.

      1. Your experience with soundz is relevant; instantaneous high current will cause unusual local (battery and cell level) effects.
        1.) Different capacity batteries discharging at the same rate results in different battery voltages. If they are in parallel the one with the higher voltage (larger capacity) will contribute more current and thus the small battery will be discharged slower. This is the ‘things balancing out’ effect my2c mentions. A far as the higher voltage battery ‘recharging’ the lower capacity one, I don’t believe that situation would occur under use if the batteries are always connected. A flat battery parallel to a charged one will have a potential difference, current will flow into the lower.However that is still normal use for a rechargeable and would at worst result in a small loss of energy as heat (recharging is never 100% efficient).
        2.) Under recharge conditions larger capacity batteries will have a lower voltage as they charge and more of the charge current will flow into it. Alternators have a max voltage such that it will not overcharge the battery; if it wasn’t the battery would be cooked once it was charged.
        What could be happening is very high current draws cause the local cell voltage to be pulled too low and the cell damaged. Also a trickle discharge (eg alarm causing the battery to be overdischarged.

  3. Cheap and easy hack to extend range. I bet this thing has a mean death wobble at speed with the two lead acids sitting over the rear tire.

    I guess she’s built for comfort, not speed.

  4. I have a 26″ bike with a brushless front wheel hub motor, 20 miles at 20 MPH from 3- 12volt (36 volt) 7 Ah batteries.
    Cost is about 50$ for 3 batteries delivered. But then again I live in Fl, pretty flat.

  5. I don’t care about speed, for health reasons I need the bike to get me to my destination and back without shutting down due to a spent battery, I want to go FURTHER not FASTER?

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