Electric bikes, and other "off label" uses for EGO battery packs

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This conversation has been merged. Please reference the main conversation: I would like EGO to build e-bikes.

I highly doubt EGO wants to get into the bicycle business, but their battery packs could easily make some waves in that space....

Some quick background:  Electric bicycles have been a "thing" for a while now.  They're basically normal bikes, but with a battery and motor grafted on.  You still pedal, but the motor makes it easier to climb hills, accelerate from stops, or just cruise effortlessly at high-ish speeds.

You can buy a "cheap" electric bike for around US$1,000 (crappy motor, crappy battery), while the fancier e-bikes can cost $5,000 or more.  There are also conversion kits that let you add the electric bits onto most any bike you already own.  A nice conversion kit also costs about $1,000. About $500 for a nice mid-drive motor, and about $500 for a ~50V, ~8AH lithium ion battery pack.

That last part should sound familiar!  EGO is now selling battery packs in that power range, and they are selling them for a very good price.  EGO's packs also include battery management, and advanced cooling technology that is comparable or better than what even the fancy electric bikes are using these days.

I'll finally get to the point:  It would be fantastic if EGO could sell some sort of "universal battery connector" that would let hobbyists of all persuasions easily connect any of the existing EGO packs to whatever they want.  In other words, a clickie battery socket, just like what the mower uses, except without the mower part!  I'm guessing that this would result in lots of people buying "bare" EGO batteries for their various crazy projects, but once they own an EGO battery pack, they'd probably also start buying the various EGO devices that "officially" use those batteries.  Everybody's happy!

(I'm guessing that EGO's lawyers wouldn't be thrilled at the prospect of people building various EGO-powered devices, and then setting themselves on fire, or wrapping themselves around a tree somewhere.  But hey, that's what disclaimers are for!)

To put it another way, I'm tempted to crack open my mower battery, just to see if I could bodge up a connector so I could also use it to power an e-bike.  But it would be awesome if I didn't have to "hack" it, and could instead just buy an official connector/holder that I could permanently attach to my bike.

Disclaimer:  I don't actually own an e-bike at this time.  But I'd like to, especially if I didn't have to buy that overpriced $500 battery for it.
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Dave Nagy

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Posted 4 years ago

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Adrian Ramirez

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If these BJTs are being used as temperature sensors, then it would explain why they don't use the T wire in the devices. Because this method of sensing temperature would require some circuitry to correlate the BJT readings into an actual temperature and would probably then be accessible through the communication through the D pin by the devices.
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Blue Angel, Champion

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Is it possible the charger could use the BJT readings to control input current via cell temperature, and the simpler thermisters would be just for monitoring temp while in use on the tools? The BMS could theoretically communicate diagnostic data (including temperature) to the tool through the data connection, since there is a battery overtemp protection shutdown while the tools are in use (solid orange light).

Maybe as you said, the BJT circuit just makes sure no one cell is heating up more than the rest?

I'll check the conductivity of the white adhesive material later, but I would assume it is non electrically conductive as it completely surrounds each transistor and is not shielded from the surface mount solder connections.

Is it thermally conductive? Yes. How thermally conductive, I'm not sure. ;-) But, it would certainly appear that its role is to thermally link each transistor to the end of its respective cell. Curiously, since the cells are connected in series, the transistor is referencing the positive end of half the cells and the negative end of the other half. If it's temperature related, I guess the temp at each end of the cell is about the same?
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Adrian Ramirez

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Yeah, it's possible that the charger uses the transistor string through the D pin to read and determine if it's going o charge and at what rate of current (usually lower current charge happens at low temperature, below 10 deg or so Celsius).

I wouldn't expect that the transistor string would be tied to the T pin though, because I wouldn't expect to see 10K ohms on my meter through them. I would think they would either read much higher or much lower depending on if they're being turned on or not at the time of measurement.

The charger definitely uses the thermistor readings for battery insertion detection and it definitely won't charge if the resistance is out of range, but the charger may also use the transistor string to determine battery temperature as a 2nd check before charging.

It would be interesting to see where the transistor string ties into the BMS and where the thermistors tie into the BMS board and which ones are connected to the T pin.

I'm not sure if the temperature at both ends of an 18650 is uniform or not. I normally place my thermistors in the center and have always assumed that would give an average. I would need to look at the cells under a thermal camera during use to see what spots get hotter.
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Blue Angel, Champion

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The white silicone (for lack of a better name) is an electrical insulator. I get no reading at all from an ohmmeter with the leads placed as close together as possible.
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Blue Angel, Champion

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Any idea what this cell is?










Markings on the cell side, top to bottom:
C
A RJ03RXA
006434

On the bottom face:
4 RJNU5

I did a little Googling but didn't come up with anything.
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Adrian Ramirez

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I have no idea. Is that cell out of the 7.5 AHr pack?

Sometimes the cell's plastic wrap (red wrap in this case) will have a part number stamped into it. It's usually a little hard to see unless you inspect it closely. If that's present then maybe that will help determine the cell type.
(Edited)
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Blue Angel, Champion

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It's from the dead 4Ah pack I disassembled.

I will have a closer look at the cell wrap when I get home tonight. I don't remember seeing any identifying markers on it.
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Blue Angel, Champion

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Sanyo UR18650RX

Jeez, you weren't kidding... the labeling is incredibly hard to see!



Rated 2050 mAh typical, 20A continuous discharge.
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Adrian Ramirez

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Awesome, glad you found that. I actually have a little experience with the RX cell. I performed a bunch of life testing on a number of li-ion cells with the RX being one of them that I was testing for high temperature applications. I didn't get too far into the testing because there was some type of internal protection that activates and disables the cell at very high temperature (much higher than the Ego products will ever see). At the time, it was one of Sanyo's newer high rate cells and i believe it succeeded the UR18650WX cell (same chemistry but higher capacity).

Sanyo is owned by Panasonic, so it looks like Ego used to get their cells from Panasonic and then changed to Samsung, maybe for higher capacity or lower price, or maybe both.

Am I correct that Ego has discontinued their 2.0 and 4.0 Ahr battery packs? I'm guessing they replaced them with the Samsung 2.5 Ahr cells and that's why they had any promotion to give away a bunch of 2.0 Ahr packs with new tools (which I took full advantage of).
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Blue Angel, Champion

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Cool! Can I ask what industry your BMS designs are used in? Sounds like some extreme environment applications.

I'm talking a little out of my league here, but as far as the source of cells is concerned it could likely be that the OEM cell producers bid on supply contracts and the lowest bidder who's product meet Ego's requirements gets the contract. Depending on the length/size of the supply contract, the same Ego battery pack could even use different cells over time based on who wins the supply contracts. This would be one of the key advantages to using a commodity cell like the 18650; plug and play compatibility with any of numerous qualifying cells.

Or from a performance perspective, it could be that the cells are selected based on battery pack configuration. Since the single string packs (2 and 2.5Ah) generally see higher load per cell than the two string packs (4 and 5Ah) and then the three string packs (7.5Ah here and 6Ah Europe/Australia), perhaps cells would be selected more based on voltage drop under load (internal resistance?) and/or ability to fast charge? The 2Ah pack charges in 25 min on the rapid charger... I'm not aware of a faster charging 18650 application.

Pure speculation on my part, for sure, but those criteria would make sense based on what I've seen in other industries. Perhaps being in the battery business you have some relevant info to add, or corrections to make? :-)

I'm not sure if Ego has discontinued their 2Ah pack or not. It would certainly seem that way for the North American market, but I'm not sure what's going on overseas. Europe and Australia are two large markets for Ego as well and they get slightly different products than we do. Also, Honda has recently announced that they are selling a line of OPE in Europe which are, for the most part, red colored and re-labeled Ego tools made by Chervon, and the only two batteries available in that line are the 2 and 4Ah packs.
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Adrian Ramirez

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I'm in the medical device field. In my experience, high volume cell manufacturers don't jump through many hoops for buyers. It might just be because my designs are very low volume (usually less than 20k annual cell volumes), and so they aren't real interested. Maybe for a higher volume manufacturer like Ego they would be willing to try and outbid each other. I was once interested in a cell that Panasonic was obsoleting due to low volume and I asked them if our annual volumes would change their decision and they said that our entire annual volume is about a half day of manufacturing for them, so that wouldn't change their decision to stop production.

That gives an idea of the large volume of cells that Panasonic manufactures.

One thing that surprised me about the 7.5 Ahr packs is that Ego stayed with 2.5 Ahr cell. They probably could have gotten closer to a 3 Ahr cell since the 3 parallel strings would cut the current requirement by 1/3, but they chose to stay with the 2.5 Ahr, 20 A cell. There is always a trade-off between capacity and power capability. if you want higher power capability, you have to sacrifice a little capacity. Or if you want more capacity, you have to sacrifice a little power capability. My guess is that they are staying with the 2.5 Ahr cell for the volume discount, even though it costs them a little capacity (maybe up to 15% capacity).

That's interesting, I didn't know that Ego had partnerships with Honda.
(Edited)
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Blue Angel, Champion

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I would imagine there are several factors at work with the 2.5Ah cells and 7.5Ah battery.

1. Since they are already buying 2.5Ah cells in large quantities for their 2.5 and 5Ah packs, using the same cell would be convenient from a supply/logistics point of view as well as takeing advantage of any volume price discount they are already getting.

2. A 7.5Ah pack is already so far ahead of any other single battery available from Ego's main competition that going farther wouldn't be necessary at this time. It also leaves the door open for the 9Ah pack that will inevitably come out in the future.

3. Referring to point #1 as well as your comment about three parallel strings sharing the load, a cheaper (low power) 2500 mAh cell could have been used instead, but perhaps the volume pricing wasn't significant enough to justify the less robust design? Or perhaps there's a thermal angle to this as well, and a lower power cell would not handle the loads as efficiently and would require the additional cost of the PCM cell wraps? It is my understanding the 7.5Ah battery does not use these and is therefore cheaper to build and more compact as a result.

As you say, with three strings of cells sharing the load, Ego could easily make a 9Ah battery right now, or even a 10.5Ah battery using one of the newer 3500 mAh 10A cells available. Some real quick and dirty math based on 50V (average) suggests the 1000W SP mower would draw about 20A at full load. That's a full load for a 20A cell in a single string battery (2 and 2.5Ah), a 10A load for a double string battery (4 and 5Ah), and less than 7A in a three string battery (7.5Ah).

Given Ego's current battery price structure, which is quite high on the larger batteries in my opinion, the cost of a 10.5Ah battery would likely be $500. :-(
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Shaun

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This reply was created from a merged topic originally titled Have you considered making an adapter for the batteries that would allow them to ....

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