Speedometer Upgrade

 That stupid little key/horn/headlight/battery 'gauge', was really driving me up the wall. That goofy little thing- I get why they put it on though, it's cheap and easy. But Electric Elk seeks to be the Mercedes of Velomobiles so that was one of the first things that had to go. 

This did take a bit of rewiring, but not much and all of the components you can buy on Amazon. I'm still trying to find some software to make a decent wiring diagram. As soon as I do, I'll make a post about fixing the wiring / installing headlights and front turn signals, etc. 

But this post is about the new speedometer/battery gauge. There is a really good and in-depth thread on Endless Sphere, but this guide will append some informaion and give parameter settings for the JX Cycle Pickup Trike.

The guage is a pretty nice, water proof, all-purpose gauge. They cost about $110 on Amazon (at time of writing), and I would say a fairly good value for the money. The one caveat is, they are not plug and play. You will need to program them a bit. But, good news, I will give you the values to set. The programming can be done in 20 minutes. 

Again- the Endless Sphere post gives a really good programming guide, that I don't feel compelled to recreate here. The two parameters you will have to figure out/set will be the signal hertz and battery levels. 

CT-22 Speedometer and Battery Guage

 

Speed and Mileage Frequency

The frequency here describes how many times the wire should receive a signal per second if the vehicle was going sixty kilometers per hour (in the case of speed). The same number is what should be set for the mileage parameter next, which is how the odometer / trip meter keep track of distance. 

Here is my math- the diameter of the rear wheel (because bike tires are measured dumb) is 24 inches, which is 60.96cm.  The formula for the circumference is Pi * Diameter which is approximately 1,915cm or 1.915m. 

60km/hr works out to be about 16 and two thirds meters per second, which would further work out that if this bike was going 60km/h the wheels would be rotating about 8.703 times per second. 

But the motor it is claimed, has a 10:1 differential, which means: for every time the wheels turns once, the motor turns ten times. So at 60 km/hr the motor is revolving 87.03 times. 

Now, it is further claimed that this motor has 32 poles, which means it has 16 pole pairs, which means that in theory for every revolution the motor makes, the signal wire should fire 16 times or 87.03 x 16 which gives us 1392Hz. 

But note, there are three control wires on the motor- a BLDC motor works by alternating which poles are activated at different times. So one hall signal wire is only going to get one third of the pulses, so divide 1392 by 3, which gives us 464 (Hz) which does seem to work pretty well. 

There is an issue though that while slowing down the speed reading spikes- if anyone has any idea why email me and when I get it fixed I'll post the solution.


Battery Levels

The battery levels are pretty easy. I will present a table here, and will update it as I dial in the numbers more tightly.   

You might think batteries should be the easiest to calculate. Figure the battery has a cut off at 48v and when fully charged is 56+v so just figure a straight line. When I asked BtrPower for the curve, that's what they told me to do, but unfortunately that is incorrect. 

Google "Lifepo4 battery curve" and you'll see what I mean ( I could have stolen an image and reproduced here, but instead I chose to respect copyrights). You may also see some good data on why LiFePO4s are better than lead-acid batteries. With a lead acid battery you do get a sort-of straight-line fall off, but with LiFePO4s its more sharp- then steady for a while, then another sharp fall off in voltage. 

As I dial in better numbers I will update this article and the "Last Update" bit below.

Parameter Description Value
0 Speed Frequency 0464
1 Mileage Frequency 0464
2 20% Battery Remaining (Charge) 0489
3 40% Battery Remaining (Charge) 0499
4 60% Battery Remaining (Charge) 0502
5 80% Battery Remaining (Charge) 0518
6 100% Battery Remaining (Charge) 0536
7 20% Battery Remaining (Discharge) 0471
8 40% Battery Remaining (Discharge) 0481
9 60% Battery Remaining (Discharge) 0484
A 80% Battery Remaining (Discharge) 0500
b 100% Battery Remaining (Discharge) 0518
d 0% Battery Remaining (Charge) 0480
E 0% Battery Remaining (Discharge) 0480

 

Last Update: October 18, 2022


 

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