Converting An Electric Scooter To Lithium Batteries And Disabling The Safeties

There’s a bunch of different electric scooters available nowadays, including those hoverboards that keep catching fire. [TK] had an older Razor E300 that uses lead acid batteries. After getting tired of the low speeds and 12 hour charge times, [TK] decided it was time to swap for lithium batteries.

The new batteries were sourced from a Ryobi drill. Each provides 18 V, giving 36 V in series. The original batteries only ran at 24 V, which caused some issues with the motor controller. It refused to start up with the higher voltage. The solution: disable the safety shutdown relay on the motor controller by bridging it with a wire.

With the voltage issue sorted out, it was time for the current limit to be modified. This motor controller uses a TI TL494 to generate the PWM waveforms that drive a MOSFET to provide variable power to the motor. Cutting the trace to the TL494’s current sense pin removed the current limit all together.

We’re not saying it’s advisable to disable all current and voltage limits on your scooter, but it seems to be working out for [TK]. The $200 scooter now does 28 km/h, up from 22 km/h and charges much faster. With gearing mods, he’s hoping to eke out some more performance.

After the break, the full conversion video.

43 thoughts on “Converting An Electric Scooter To Lithium Batteries And Disabling The Safeties

    1. Standard cap values are 25v, 35v, 50v, etc. If the original board ran at 24v I would hope they used at least 35v caps. For the new battery setup 50v caps would be sensible.

    2. That and watch out for MOSFET voltage rating. The higher voltage can also cause higher transients spikes during switching. If they don’t have a good snubber or higher voltage rating MOSFET, that could cause some issues.

    1. It’s also illegal to drive after the modifications.

      There are some specific power and speed limits to devices like electric scooters, and if people start to “tweak” theirs, it won’t be long before any DIY electric scooter and e-bikes becomes de-facto illegal because you can’t prove that it meets the legal requirements to a policeman on the street. Just because some boiler plate you yourself put on says “250 W” doesn’t mean they’ll believe you.

      1. Where I live, two wheeled electric vehicles are classified as bicycles as long as they have functional pedals, regardless of power output.

        No license required to drive. In practice no way to get a ticket, and reduced parking fees. You can modify them as long as it’s not the most absurd thing on the road, which is truly difficult (I’ve seen golf carts carrying live chickens on the highway. No cage. Just chickens.).

        They mainly use lead acid batteries though which are a pain to recycle+replace every 14 months, and the ~20km range gets a bit limiting. Bikes with lithium based batteries have just hit the local market and most are pretty bad, but you can buy large lithium-iron battery packs that look pretty good.

        I was looking at the feasibility of doing exactly that so this article was helpful!

        1. Where do you live, legionlabs? I was amazed when I was in China at how ubiquitous and useful even just their basic lead acid bicycles and scooters were. and so cheap too. I wanted to bring one home so bad.

      2. it may be illegal but.

        1. with the way that lithium fires are going we may be forced to upgrade if the scooters are shipped without batteries due to the governments refusing to let them into the usa.

        2. police officers do not have technical skills except for individual officers who may work on electronics on the side so if you are lucky ok unlucky enough to have that officer pull you over then he may know but most officers probably wont notice.

      3. Omg! Are you being serious. As if we dont already have big brother breathing over our shoulders peeking in on everything we do. Now we are suppose to make sure our little backyard fun projects with a 15mph electric scooter meet all safety regulations. You’re that guy that gets mad when people almost come to a complete stop before continuing thru a 4-way stop.

  1. Hope the controller and motor will survive that power increase. One thing to notice, he replaced 9Ah power supply with 2.6Ah one, so the mileage will be severly reduced. However, if experiment works it shouldn’t be a problem to add more cells, there is enough space.

    1. 7 Ah -> 1.4Ah, but yeah, you’re on the money. Range on the Ryobis is poor but they did their job as a proof of concept. Eager to get some serious lithium packs in there soon!

    2. The other thing to take into account is the internal resistance of the battery, the discharge curve and the effect of low / high temperatures. These affect the usable capacity of the battery… and the life.

  2. Hi all. I did a simpler LiPo upgrade to my E200. It occurred to me that the two heavy lead acid gell-cells, with a drop dead voltage of 22 volts, could be replaced with 7 lightweight 5000mAh or 5Ah LiPos with a drop dead voltage of about the same voltage (22.4V), and the low battery light would still be useful. Plus… The Gell-Cells have poor current handling ability, and in my experience of almost daily use (for shopping and Dr. appointments and such) only survived for about 6 months. The LiPos I planned to use had a 20c rating, which meant that they could handle 125amp of discharge current, and since the scooter is limited at about 30amps it meant that I would have lots of headroom/safety margin.

    The pack I chose was a Zippy Compact 7s 20c 5Ah battery from Hobby King. I put XT60 power connectors on the pack and speed controller (Good to 60 Amps). I also used an expanded scale voltmeter as a gas gauge to measure the top 7 volts of the battery pack so I would know when I was half way and had to head home. There is plenty of room for two of these batteries in parallel in the tub. I use an Accucell 8 Lipo ballance charger and hacked it to transmit battery info to LogView running on my lapTop. You don’t have to do that part, but it’s sooo Cool.

    The performance didn’t change much, but the first thing I noticed was that it was easier to carry the scooter up stairs or onto a bus, and that the range was the same as the 9Ah GellCells. The first pack laster for two years before It was unusable even to go to the store and back (about a kilometer).

    I’m going to do the current limit hack if I can, when I get some new batteries. Dang Canadian customs. 8-(
    HobbyKing has 6600 mAh and higher packs too.

    1. Stephen, I’m very interested in your setup! There’s a dismantled electric wheelchair in front of me right now, which I’m tuning up for my mom to use after knee surgery this summer. I got it without batteries, and I was looking at using a 6S or 8S lipo pack (7S seems really uncommon) from hobbyking.

      The trouble is charging. All the hobby-focused chargers require user interaction to begin a charge after you plug them in, but at least they include balancing. I was looking at a Noco Genius charger which is simpler to operate, but doesn’t have a balance connector. I could use that charger and put on a separate balancing unit and run it manually once in a while, I suppose, but that’s tricky for its own reasons.

      Really, I’d like to find something LiFePO4-based for safety’s sake (they don’t seem to burn down houses as often as LiPo’s do) but the hobby market seems to ignore them, and the LiFePO4 power-tool packs are incredibly expensive.

      Thoughts?

      1. I hear ya bud. (is that too informal?) I would like to be able to take my charger with me so I can go to the mall that’s about 5 klicks away (Full range for my setup), but I’m afraid that if someone saw the deck off the scooter, a rats nest of colored wires going into a metal box with incomprehensible text on a lighted display and a “Black box” plugged into the mains, they just might call the bomb squad. That would be embarrassing. B-) Plus, I’d have to bring a power screwdriver for all those screws.
        What I’ve noticed about my 7s pack, is that it stays in balance quite well usually. It’s only when it gets too depleted that I NEED to re-balance it. I hate to sound like an ad for hobby king, but they have a balancing meter (CellMeter 7) that you could leave plugged into the pack if you wanted. You can start that when you plug in the simple charger, but it is slow on large capacity batteries.
        If there is a “Suggest a Hack/Project” forum here at HackAday, I’d post there. The only simple chargers I’ve seen are for 4cell packs. I suppose you could pull the balance boards from a couple of laptop batteries, make 2 packs and series them together. I don’t know what your skill level is though.
        I think that the “Charge blind and balance occasionally” method is going to be your best option. The charger just has to be able to stop when it’s full.
        I used to use a 50v psu for power, 2 12v 1amp lightbulbs to limit the current, and a home made charge level detector with a power FET to shut the whole thing off. I never blew up the battery or burnt down the apartment, but I never felt like I could turn my back on it either. I don’t recommend this for you, or anyone, though. Least of all, your Mom. ;-)
        Sorry I couldn’t be more help. This is one of those “Scour the web, or build it yourself” situations, I guess. Good luck.

        1. I just wanted to add, that since LiPos are about 1/5 the weight and usually much smaller than Lead acid/Gel Cells, You should have lots of spare room in the battery box for either more batteries, and/or a charger setup.

          1. So I’ve spent the last few hours on http://www.wheelchairdriver.com/board/index.php reading a zillion things about the incredibly badass chairs that Burgerman and Williamclark77 have built, among others. Those are all-day powerchairs and in a whole ‘nother league, of course, but there’s a lot of good info in there about batteries that I can use even on a considerably lighter-duty build.

            I’m looking at a “first pass” to get the chair driveable, using some cheap lead-acids I have sitting around, and if she gets a lot of use out of it, an “upgrade” to a lithium setup with a better charger, onboard inverter, etc. I’m learning a lot about balancing and BMSs, and trying to come up with something that charges immediately when plugged in (zero button pushes) and is mom-safe throughout the process. Tricky! :)

  3. That’s a neat little trick you have there, I will certainly do this to add more room in my battery box. How long do these batteries take to charge? At the moment the battery on my electric scooter takes a whopping 24 hours to fully charge, which is annoying and I would like to reduce this.

  4. Hey getInLine79:
    LiPo/ions usually take a 1 C charge. So a 1Ah bat takes an hour at 1 amp. a 3Ah bat takes 1 hr at 3 amps. Lower charge rates… do the math. Ah / A = Hrs. For better battery lifespan, lower is better, but 1C is just fine for a quick charge.

  5. I’m trying to change my razor crazy cart to lithium fast charge. It runs on two lead acid batteries. They are 12v 1.5ah batteries. I want to do a basic swap with greenworks hand tools or Ryobi. Can I do this without having to gut the whole thing out and put new hardware?

  6. Lead acid cells are rubbish in the winter here in the UK. I upgraded my 24v lead acid pack with a 7 cell lithium on my mobility scooter…. Will have to take some photos of the conversion, I did a freestyle hack one day, so no photos. The new cells with BMS fit nicely into the original battery module. Did a pneumatic wheel conversion recently also.. but that’s OT.

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