Battery Guage LEDs

[Vroooom]

I have a Magic Pie 3 with a 48v battery pack and a 48v wuxing twist throttle. The Magic Pie motor and throttle work fine.

The battery guage / capacity doesn't work - meaning none of the LEDs light up. How do I diagnose the problem?

I've already taken a measurement of the battery voltage and it read 51v. I'd like to test the voltage between the connectors but I'm not sure whats the best way/method to do so as the holes are pretty small.

[Bikemad]

I used a couple of resistors as their legs are just the right diameter to fit into the sockets and make a good contact without damaging the socket section.

If you have battery voltage at the throttle connector on the main control harness then the problem will be inside the throttle unit or within its cabling.

As everything else is working, it might be easier to fit a separate voltmeter or battery gauge wired direct to the battery connector, as the throttle mounted LEDs do not tend to be very accurate with lithium batteries. (Although they should be a lot more accurate if you are using lead acid batteries.  )

Here is a very neat little gauge that shows the approximate battery capacity based on the battery voltage, I have one of these waiting to be fitted into my 48V 10Ah GM Battery:



If fitted from inside of the end cap and suitably attached and sealed using silicon sealant and a hot melt glue gun, it should be well protected from the weather.

I will try and document the process involved when I eventually get around to modifying my battery pack. 

Alan
 

[Vroooom]

When you say the throttle mounted LEDs are inaccurate - do you mean they underestimate or overestimate the amount of battery remaining?

Where can I buy your shown battery gauge?

[Bikemad]

The LED gauge greatly overestimates the remaining battery capacity because it was designed for the lower voltage lead acid battery.
Check out this thread for more details.

The gauge shown in the previous photo was purchased from here on eBay and can also be used with a wide variety of batteries.

Here are the results of some test voltages applied to the gauge via a variable voltage power supply:



The 14S LiPo setting seems to work reasonably well for the 48V LiFePO₄ battery.

Alan
 

[Speedsterharry]

I wonder if it's possible to modify the original gauge for LifePO4 display ? Anyway, the replacement of this part by this voltmeter/gauge is a good idea, I might just do that...

[Thuktun]

I bought a 36v throttle but soon after getting my bike started using 48v so I did something similar to Alan. I got a digital voltmeter on eBay for about $3 and mounted it to an old base for a cycling computer. It's smothered in epoxy for waterproofing. I've had my bike for a couple of years now, ride it in all sorts of weather, never a problem. It doesn't give me a percentage though, it tells me the voltage. I can guesstimate how much I have left from that from experience.