(Mis)using a Priority Current range extender: should I expect fire damage in my future?

[riding_on]

So I'm using a Priority Current with the range extender, and have a need for more range than the downtube battery & rear rack battery can provide (I don't own a car anymore). The way Priority has it setup, the range extender comes with a cable that replaces the downtube battery's cable to the mid-drive motor (which is, I believe, a Truckrun motor if that matters). You unplug the downtube battery from the motor, plug the downtube battery into the range extender cable, and then plug the range extender cable into the motor where the downtube battery was previously plugged in. There's a cell phone sized controller in the range extender -- two wires run from the rear rack battery into that controller, and four run out of the controller. I assume that two are the input from the downtube battery (see below), and that two are the output to the motor.

It doesn't "blend" the batteries or balance them. What it does is drain the downtube battery to approximately 30%, then switch over to the range extender battery and repeat. What happens after the range extender itself hits 30% I can't tell you, but I can report that the LCD display at some point goes from 30% right up to 70-90% in a matter of seconds when it appears to switch. If the rear rack battery is powered off by using the on/off switch on the battery itself, the display goes dead (it doesn't swap back to the downtube battery fast enough). It'll power back up if the rear rack battery is left off and you try to power it on though.

Like I said, I have a need for more range than I get from the combined 22Ah (10Ah downtube + 12Ah rack battery, or 500Wh downtube battery + 576Wh rack battery) supply. When I recognized what the range extender controller appears to be doing, I decided that as long as the secondary battery is of the appropriate voltage (48v), it should work even if I used a 24Ah, 1.2kWh battery I had left over from a previous ebike that I destroyed tinkering with. So I spliced 12AWG wires into the positive/negative wires that run from the rack battery to the controller in the rack assembly. I also tested the voltage from the rack battery when it's powered off, and those wires read as 0.4 volts when the battery's switched off.

So I've now got an XT60 connector spliced into the rack assembly, and a third battery mounted to the top tube (48v 24Ah downtube style). When riding, I let the stock Priority downtube battery drain, keep the rear rack battery plugged in but switched off, and leave my added third battery -- the 24Ah one -- plugged into the XT60 connection. The controller switches over to the third, added battery at about 30% of the stock downtube battery's remaining charge.

If I drain my 24Ah battery until the LCD display reads almost empty, I stop, power down the bike, unplug the XT60 connector, and flip the switch for the rack battery to the "on" position. I then power the bike back up, and the LCD display reads 50-80% battery remaining; I then continue on my way.

My question is this: am I begging for these things to catch fire someday, and how badly am I abusing these poor cells? My third battery (48v 24Ah) is a LiFePo4, but I have no idea what the two Priority batteries are.

 

[amberwolf]

What I would do, if possible for your system, is wire all of the batteries directly in parallel, if they are all the same chemistry (same full charge voltage and same empty voltage) and same state of charge (actual voltage at the moment of connection). ***

This makes it easier on all of them, because none of them has to supply as much current, so there is less internal heating and wasted power in all of the packs, and you'll get a tiny bit more range out of them just from that.

There are caveats: Unless all three packs use common-port BMS, where both charge and discharge are wired to the same port on the BMS board, you'll need to disconnect the discharge ports before charging each pack. And if charging them in parallel, you'll need to disconnect the charge ports before reconnecting the discharge ports. Otherwise the other port not being used will allow current to flow around a BMS that has turned it's other port off to protect a pack from overdischarge or overcharge.

If they're common-port, then direct paralleling of the packs is simple and can be left taht way for charge and discharge.


*** as long as the charger voltage (if all charged at once from same source) is the same for all packs, *or* is no higher than the lowest pack's HVC (full voltage), *and* the controller's LVC is above the lowest pack's LVC, then even different chemistries could be used.

 

[Diggs]

I directly parallel a Luna Shark pack (14s4p) with a home built 14s5p that is using a 2-wire BMS. The Shark has two XT90 outputs One going to the motor and the other used for direct connection to the second battery pack. Different cells and different BMSs. I charge through the XT60 charge connector on the Shark pack and only charge to 90% when the two are connected and separate them and charge to 100% for balancing about once a year. They are 5 years old now with no perceptible loss of power. I should have an extra fuse or two in there but never got it done.

 

[fechter]

The issue I see with your current setup is if you forget to turn off the rear pack and plug in the third one. This could possibly allow excessive current flow and smoke something. A more foolproof approach would be good.
One way would be to put XT60s on both rear packs and manually switch between packs so there’s no chance of connecting the rear packs to each other.

 

[riding_on]

So I kind of consider it an obligation to correct my misinformation from my original post: I was wrong about the way the Priority Current's range extender is working. I added an inline ammeter, and lo and behold, it actually is blending the batteries at a certain point. All I can say for certain is that it's definitely drawing what looks like half of the total current from the second (in my case third) battery. I just wanted to make sure I didn't leave FUD hanging around. Sorry about that, but I had no way of knowing until I got a closer look at the watts it was pulling, and from where.

In fact, it sustains 930 watts (~18A) for a good hour straight. With a 500 watt motor. Neat trick!

 

[-dg]

So I kind of consider it an obligation to correct my misinformation from my original post: I was wrong about the way the Priority Current's range extender is working. I added an inline ammeter, and lo and behold, it actually is blending the batteries at a certain point. All I can say for certain is that it's definitely drawing what looks like half of the total current from the second (in my case third) battery. I just wanted to make sure I didn't leave FUD hanging around. Sorry about that, but I had no way of knowing until I got a closer look at the watts it was pulling, and from where.

In fact, it sustains 930 watts (~18A) for a good hour straight. With a 500 watt motor. Neat trick!

Very interesting. I got a Current back in September and it's been great, I've ridden more in the last few months than the past several years. It really hits a nice balance between ride experience, features, quality, performance and value. I've been shopping for a friend and nicer bikes cost quite a bit more and cheaper bikes mean giving something up.

Now that I've gotten used to riding again, I'm thinking about longer trips. Nothing crazy but on assist 3 I get 22+ miles, on assist 2 it's like 27. I'd like to get 35-ish. I'd just get the battery extender but the rack it comes with won't work with my bags etc. I'm thinking a small battery, like a 200-ish Wh bottle battery connected to the extender controller would be about right. Any idea where to source the controller wire harness or even just the connectors?

Also, what are you doing that uses 930 watts for a hour? How fast is that?

Finally, in the other thread you mentioned that it would not give 900 watts on just the torque sensor. How much will it do?

 

[999zip999]

So a 12ah a 10ah and a 24ah lifepo4 battery. The first two lithium ion ? So 46ah of batteries? I'm confused.
Sounds dangerous. How many miles do you need to go on one trip in one day ?

 

[riding_on]

Very interesting. I got a Current back in September and it's been great, I've ridden more in the last few months than the past several years. It really hits a nice balance between ride experience, features, quality, performance and value. I've been shopping for a friend and nicer bikes cost quite a bit more and cheaper bikes mean giving something up.

Now that I've gotten used to riding again, I'm thinking about longer trips. Nothing crazy but on assist 3 I get 22+ miles, on assist 2 it's like 27. I'd like to get 35-ish. I'd just get the battery extender but the rack it comes with won't work with my bags etc. I'm thinking a small battery, like a 200-ish Wh bottle battery connected to the extender controller would be about right. Any idea where to source the controller wire harness or even just the connectors?

Also, what are you doing that uses 930 watts for a hour? How fast is that?

Finally, in the other thread you mentioned that it would not give 900 watts on just the torque sensor. How much will it do?

That post I made actually made me pay more attention (I don't stare at the gauges when cycling, normally, hah), and I was wrong. It only sustains 900 watts for a brief period before dropping down to the 600-700 level range. My throttle seems to push the motor harder than it normally can be pushed, if it's only responding to the torque sensor and pedal assist. It seems almost perfectly tuned to never, ever overheat when used the way they sell the bikes. I've seen my throttle overheat the motor once or twice (I've put over two thousand miles on it and totally ignore motor temperature, so generally speaking, I don't consider it as even being much of a possibility).

As far as wire harnesses, I think you're absolutely out of luck. When I asked Priority about the throttle, they told me it can't be done (which is funny, because I had already done it when I asked them about it, heh). I believe they're rebranding Leaf bicycles, a Chinese company, if that helps you out any. The motor itself is a Truckrun product. M01 is the model on Priority Currents. Truckrun is the Chinese brand, sometimes called Wuxi Truckrun, but I think they're just *in* the Wuxi area and the company itself is just Truckrun. M01 is the model of motor.

What I did is strip and splice individual wires and leads. I used a Bafang throttle and extension cord, which had the right connectors, but the wires didn't match -- I think they're called pinouts, but I don't really do hardware, so I'm not sure. I had to solder the wires to rearrange them myself.

 

[riding_on]

So a 12ah a 10ah and a 24ah lifepo4 battery. The first two lithium ion ? So 46ah of batteries? I'm confused.
Sounds dangerous. How many miles do you need to go on one trip in one day ?

I go 50 miles at a time, on rare occasions. 30-35 is my usual trip. And I just like having lots of energy to spare, in case I want to take a detour. I use ebikes as car replacements, don't forget.

 

[999zip999]

Wow that's a lot of miles that was my second question my first question is about your two different batteries one's lifepo4 and the other is ??

 

[riding_on]

Wow that's a lot of miles that was my second question my first question is about your two different batteries one's lifepo4 and the other is ??

Yep, one is LiFePO4. I have no idea what the stock batteries (in-frame and range extender) are.

 

[999zip999]

Do you use one battery at a time ? As the different chemistries have a different HVC and LVC. As I believe in just guessing now that the other battery is lithium ion ?

 

[calab]

manually switch between packs

Thats the way to do it, you could use XT90's for better finger grip.