Using power tool batteries (drill & string trimmer) to power a tsdz2 (48v motor)

I would like to "underdrive" a 48v motor. Is it possible? The rationale is to use batteries that I have on-hand (so the up-front project cost is low). I'd rather not buy a 36v motor and then later get the urge to upgrade to a 48v motor.

I know overdriving is a thing per
this post:

eyebyesickle said:

casainho said:

We know there are 2 type of motors: 36V 4000 RPMs and 48V 4000 RPMs (this later works at 52V also, is the same motor). As for the controller, is just the same for all different configurations: supports from battery 20V up to 60V.

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Yes, you can run 52v/14s on EITHER motor actually, the '36v type' motor will just spin a little faster with less torque than the '48v type' motor - but they both are compatible.

I call running 48-52v (54.6-58.8v) on the 36v(42v) motor 'OVERDRIVE'

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These are the batteries I have on-hand:

Two Ryobi Ni-Cd 18v 3.5 Ah 63 Wh (for a drill):


Two Black & Decker Li-ion 20v (really 18v) 30 Wh (for a string trimmer and other things):


If I understand correctly, the firmware can be configured for any voltage between 20v and 60v, correct? Would it be sensible to wire each pair of my appliance batteries in parallel, and then serialize the two sets, to effectively have a 40v 93 Wh battery power a 48v motor? Is there a problem mixing li-ion with Ni-Cd? If so, I suppose I could just use 2 batteries.

93 Wh is not enough. That's under 10 miles of assist even if you pedal hard and go slow.

36v on a 48v system should not be a problem if you can reprogram the controller settings. I can't confirm the ultimate voltage range on the TSDZ2, you would want to check google or the product specs for that.

You would not want to mix lithium and NiCd under any circumstances. Different discharge curves. So the packs will want to be at different voltages as they go from full to empty. Could probably cause fire.

The gist of your post suggests you are trying to scrounge stuff you have on hand because "batteries are expensive". How much did the rest of your bike cost? You have a nice drive unit. It doesn't make sense to handicap a nice combination of parts with almost no battery at all.

flat tire said:

93 Wh is not enough. That's under 10 miles of assist even if you pedal hard and go slow.

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I'll generally cycle ~3 miles each way. It's very hilly, but I would only use the motor on climbs. I'd figure each charge needs to serve about 3 miles climbing in total. But I do not like the sound of "pedalling hard and slow". I don't need the motor when flat but my intent is to make the uphills go away, in effect.

flat tire said:

36v on a 48v system should not be a problem if you can reprogram the controller settings. I can't confirm the ultimate voltage range on the TSDZ2, you would want to check google or the product specs for that.

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Glad to hear that. Since the 36v motors cost about the same as the 48v ones, there doesn't seem to be much reason to go with 36v.

flat tire said:

You would not want to mix lithium and NiCd under any circumstances. Different discharge curves. So the packs will want to be at different voltages as they go from full to empty. Could probably cause fire.

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Thanks for the warning. Guess I'd have to favor the Ryobi Ni-Cds in principle, for the 63 Wh. Although as you say, it may be insufficient.

flat tire said:

The gist of your post suggests you are trying to scrounge stuff you have on hand because "batteries are expensive". How much did the rest of your bike cost? You have a nice drive unit. It doesn't make sense to handicap a nice combination of parts with almost no battery at all.

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The bike was $150. It's a Mongoose fat bike in decent condition, except one of the pedals is stripped to the point that the crank needs to be replaced (or I'd need a tap kit). That's why it was cheap in fact. So I figured I might as well install a mid-drive to fix the crank and make it useful in a hilly area. I'm considering power tool batteries for a few reasons:

• batteries are on-hand
• versatility -- when a battery is near the end of its life, I can repurpose it to string trimming or drilling.
• it's my first e-bike conversion, and if something goes wrong it's a small loss if I didn't have to buy a battery.

If the makeshift battery can't handle the job, I won't mind upgrading it. At that point I will at least know that the motor installed okay and functions okay, even if just for a minute. I'm also thinking if I do upgrade it, I might be tempted to go with an Ego battery. I have nothing from Ego but since I have a lot of power outtages perhaps I should have some portable power. Maybe this is all crazy talk, but I guess I'm a sucker for versatility.

1) You apparently have barely any batteries on hand
2) You won't be doing much of anything useful with the battery at end of life
3) If you want an ebike you want a good battery. "Oh I'll go halfass with an ebike that barely has a battery because OH GOD I don't want to spend money to get a GOOD ebike"
4) You can get a lot more juice for less money with an ebike battery vs the hardware store stuff and there's about a million devices out there that will convert the battery juice to outlet AC power. The versatility is in having a battery, not in having a particular system.

Oh also you say you want the ebike to eliminate the uphills. You could just gear down and go slow on the uphills if it's too much effort. But, that's essentially what you're doing on the flats already. Ebikes are good to go faster everywhere with less effort. Stop being such a cheapskate. Going thru all the effort to make a nice mid drive bike that "only works on uphills" is just dumb.

xtinctionRebeller said:

I would like to "underdrive" a 48v motor. Is it possible? The rationale is to use batteries that I have on-hand (so the up-front project cost is low). I'd rather not buy a 36v motor and then later get the urge to upgrade to a 48v motor.......

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Besides the strange thought for using these batteries. If you use a 36V li-ion battery for a 48V motor. Than the rpm is lower than 4000rpm max and by that the max cadence is lower too. Uphill you want mostly a higher cadence than on the flat. Besides lower cadence uphill give a lot stress on the motor gearing.
Also the max power must be limited, because with the same power at a lower voltage you need a higher current what gives also a more heating of the motor. So imho there is no benefit of underdrive a motor for that purpose.

> Going thru all the effort to make a nice mid drive bike that "only works on uphills" is just dumb.

I used to have an Ahooga. These bikes are designed precisely for urban cyclists who encounter hills and don't want to break a sweat on the way to the office. They're marketed as "hybrids" -- the idea being that these e-bikes are not for someone who wants to be entirely lazy. The motor felt insignificant (nearly useless) when cruising along on flat ground (unless there was a headwind). On climbs the small 250 watt 24v rig needed my help but it was very adequate. My effort and speed was just the same on most hills as riding flat. It was a perfect balance. I would not go pure muscle bike though, because some inclines are ball-busting even in the lowest gear, and I sweat like a pig. It would actually be easier to get off the bike and walk it up some hills (e.g. when the battery ran out). That's a non-starter in the extremely hilly region I'm in now - I don't want to take all day.

I no longer have the Ahooga. In converting a fat bike, I do believe mid-drives are the best place for a motor, and ATM I have a broken crank to deal with anyway, so it just makes sense to install a mid-drive even though I don't need much power. But if the Ryobi batteries are non-starters, then it seems I need to overshoot my needs. I didn't realize non-universal e-bike batteries were the best value, so maybe that's the answer. I was assuming there's a bigger market and more competition on power tool batteries.

flat tire said:

4) You can get a lot more juice for less money with an ebike battery vs the hardware store stuff

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I decided to put this to the test. The results show the contrary. All but one e-bike battery costs over $10/Ah.

I think the results may be lying, though, because the power tool batteries mostly have lower voltages, which I suspect means they would be spending more amps per hour than a high voltage battery. So perhaps the calculations need to account for the cost of more low voltage batteries wired in parallel. IOW, perhaps I need to triple the "price/Ah" on all the 20v batteries. I probably need to calculate watt hours to make the comparison fair.

I realize e-bike batteries have advantages, e.g.:

• lower heat b/c of higher voltage
• chargers included in the price
• mounts easily on a bike and often lockable
• water resistant
• possibly renewable by end users (cells are sold separately by bike shops, suggesting a dead battery is meant for consumers to open and swap in new cells). This does not seem to be the case with power tool batteries.

But strictly w.r.t. juice for the money, I think power tools would still have the edge by a slim margin if I were to compute watt hours.

xtinctionRebeller said:

flat tire said:

4) You can get a lot more juice for less money with an ebike battery vs the hardware store stuff

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I decided to put this to the test. The results show the contrary. All but one e-bike battery costs over $10/Ah. .............

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This comparision is a strange one.
Because the voltages (= number of cells) are different, you can't compare costs/Ah. Only costs/Wh.
So better is to recalculate this table by multiplying the voltage with Ah to get Wh.
In that case the difference between the most cheapest and most expensive is a lot less and you will see that the Emotion has the same price as B&D

Dsanke B&D the 18V*5Ah= 90Wh > $29 = $0,32/Wh
E-motion bottle battery 52V*12Ah = 624Wh > $202 = $0,32/Wh

I need to know how to compute watt hours. I cannot simply use the product of advertised voltage and Ah, because marketers sometimes round voltage up and sometimes not. Should I assume that "20v" is really "18v" and "40v" is really "36v" (10s), and that "52-60v" is really "52v"? Or is that still flawed, because the voltage is really multiples of 3.7v cells?

I'm also baffled by the Powerworks battery specs on the power tool table. If I trust the Wh figure that was in the specs, then that makes the voltage 54v. Would it make more sense to assume the battery is actually 52v, and that the Ah is really 5.19?

I suspect Ah is usually rounded to whole numbers. I don't suppose I can do anything about that.. perhaps that's not a show stopper since the calculations are used comparatively anyway.

(update)
I've made the voltage assumptions to calculate price/Wh.

Conclusion ATM: if a rider happens to have enough power tool batteries on hand to power their e-bike, then it probably makes sense to rig the bike to use them. But otherwise if it's necessary to buy a battery for the project, then it's probably more sensible to buy an e-bike battery.

(update 2)
The "Green E-motion" battery just jumped up in price. The next best value is $0.33 per Wh but I nix that b/c it's Paypal only (thus dodgy & unethical). I find power tool batteries to be a clear winner in juice for the money.

I use greenworks 40v tools for my ebikes, mower, trimmer and chainsaw. I buy the off brand replacement batteries for about $75 for 40v 6ah and parallel them for the ebike. If I were riding longer distances I would definitely go in for a bigger decent ebike battery.

The midpoint voltage is used to convert from Ah to Wh.

Most LI batteries in tool packs are ~3.6Vpc, if you plan to stop 10-20% from the bottom for longevity, you could use 3.7V

A good battery pack can easily cost more than the rest of the bike, but it's worth it.

Figure 200-300 cycles if you take care of it well.

xtinctionRebeller said:

If I understand correctly, the firmware can be configured for any voltage between 20v and 60v, correct? Would it be sensible to wire each pair of my appliance batteries in parallel, and then serialize the two sets, to effectively have a 40v 93 Wh battery power a 48v motor? Is there a problem mixing li-ion with Ni-Cd? If so, I suppose I could just use 2 batteries.

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You can do anything with our develop OpenSource firmware, any motor and battery voltage, including configuring the motor current ramp, battery max current, very accurate battery SOC and automatic battery internal resistance calculation.

https://github.com/OpenSource-EBike-firmware/TSDZ2_wiki/wiki/Features-and-configurations-on-display