Power Meter on ebike

[JustAroundTown]

First let me say thanks for your time and effort to help! I believe that the gauge/meter (See photos: Outside Power Meter, Top of Power Meter) that shows the charge to my battery is bad (I refer to it as the power meter). I believe this board is bad because: When I measure that voltage of the battery directly I get 51.2 volts (48v battery). When I measure the voltage at the input of the Power Meter board it too shows 51.2volts (See photo: Bottom Power Meter). When I press the button on the board which is supposed to display the status of the battery the voltage drops to 1.1volts (See Photo Top of Power Meter). I checked the board and there is no evidence of damage on top or bottom of the board (See photos: Top Power Meter, and Bottom Power Meter). First should I just replace board without any further investigation? What would cause this board to go bad? Second how to I get this board only, without buying a complete new battery and case? I've found that because this appears to be a Chinese product getting things like schematics and additional information is difficult. There doesn't appear to be a serial number on the board. The bike company appears to have gone out of business. There's more to the story but trying to focus on one thing at a time. If needed by someone then I'll elaborate.

Again appreciate that your taking your time to help!
Scott

 

[amberwolf]

I'm going to use the term Battery Meter instead of Power Meter because power meter is usually used in reference to things like wattmeters that tell you much more than just the basic battery level, which is all yours appears to do.

Does the actual battery voltage on your multimeter drop when the battery meter is activated?

Does the bike not work correctly? (not turn on and power the motor)

If those are true, it usually means that the BMS of the battery has turned off the output to protect the cells against overdischarge or some other problem like badly unbalanced cells (caused by some cells aging and failing faster than others).

Even when off, there is "leakage" thru the BMS FETs, so you can still read a voltage until some load (even the tiny one created by the battery meter LEDs) is applied.


You can test the battery meter on it's own using your charger, without the battery, by connecting the battery meter's + and - to the charger's + and -. If the meter works normally, the problem is not the meter.


The meter itself is just a quad comparator chip and some LEDs driven by the different outputs, with resistor voltage dividers on the comparator inputs, setup so each LED is turned on as long as it's comparator is detecting voltage above the limit set by it's voltage dividers.



If you just want to buy a new battery meter similar to that one, there's plenty of them out there, though probably take a while to find one that matches the one you have closely enough to fit directly in the same spot that one does. This is one possible search to find them on Amazon, for instance. amazon battery meter - Google Search
Another specifically for LED versions

Google Search

Sometimes they use gauge instead of meter

amazon LED battery gauge - Google Search

Myself, I'd rather use an actual wattmeter, because it will tell you a lot more about your system and battery, and is useful for troubleshooting a number of problems. They are wired into the system differently, but can still be mounted at the battery.

Google Search

There are also things like the Cycle Analyst from Grin Tech that do even more (not just a power meter but also able to modify behavior of the bike in certain ways depending on how you wire it up and setup the menus), but that's probably overkill.

 

[JustAroundTown]

e-bike repairs



Amberwolf, I appreciate your response! All guidance is valuable!

Yes when I depress the button on the battery meter the voltage drops to 1.1v from 51.2v.

No it’s not working.

Test prior to starting the blog:

Placed bike on stand and then powered it up. The computer booted, lights/horn worked. BMS values looked normal “to me”.

Took bike for a ride. It got ~ 6 blocks down the street and lost all power. I pedaled it home.

If I measure the voltage on the battery it shows 51.2v.

I disconnected the battery meter (see schematic recently uploaded) and connected it to my power supply (max 32v output) and the battery meter doesn’t light at all. Do I need to retest using charger. I was only trying to save wire since I don’t have much wire to work with or space in that end cap for extra wire.

Put the battery on bike without the battery meter connected to system and the horn would sound! Very weakly and eventually stopped.

ps. Additional details are in my prior blog post. Just in case that information is of value. Also if I can present the details in a better way please share your thoughts! I'm here to learn as much as I am to fix this issue!

Again I appreciate your expertise!!

Scott

 

[amberwolf]

Since the battery itself doesn't operate the bike correctly even with the battery meter not connected to it, it is likely the battery itself has a problem that has caused the BMS to shutdown it's output (and possibly the charge input too). You'd have to measure the actual cell voltages inside it to see if one or more of them has dropped below the safe recharge limit, usually about 2.8v or less, where the BMS shuts off the input / output FETs to prevent cell damage and potentially a fire.

If it's a 48v battery, that's usually 13 series cells or groups of cells, for about 54v full, and about 40-42v empty depending on controller LVC and / or BMS LVC. So when measureing you should end up with 13 sets of voltages, starting at the most negative cell (group) going up to the most positive. Normally for a functioning pack of well-matched balanced cells that's at 51.2v, each of those voltages should be about 3.94v. What you will probably find is that you have say, 12 groups around 4.something volts, and one group down below 3v (which will be the one causing the problem).


I expect the battery meter is probably working fine, and is not causing your problem, but it should be tested to be sure. Since the battery meter is designed to show empty at something like 10v above your 32v power supply voltage, I wouldn't expect it to operate on that (it might show the empty LED lit, perhaps dimly, depending on component choices they made). You'll need to test it using a voltage supply that is within the range the battery would be for the meter to operate as expected / designed. The charger is the simplest one to use for this, becuase the meter will show full with this, assuming the charger doesn't have to detect the battery first to output a voltage (some do, many don't).



Regarding the "blog", I don't know where that is posted, so if you have info there that isn't here, but is relevant to this problem, I recommend copying that info to this thread, since your two posts in this thread don't have any links to any external websites or other threads. There also isn't a schematic in either of your posts.


If by not having much / enough wire you just mean you don't have spare wire laying around to connect and reach things, you can scrap old cables from computer stuff for certain kinds of low-current testing wiring, and old wall-AC cords for higher-current testing wiring.

 

[JustAroundTown]

amber wolf, Ok I did as you asked and yes the battery meter is working. So assuming that my next step is to check the battery (the individual cells) how do I get it out of the case and more importantly how to do this safely? I'm a little apprehensive working with these battery types. I'm assuming it's Lithium-ion! The battery itself appears to be glued into the case. I don't seem to be able to slide it out of the case. When I look down he case from one end to the other. I can't see completely from one end to the other all the way around the battery! I haven't but will go look to see if there is a spot on this site for safety advice.
Thanks !
ps. I attached the "schematic". Obviously is my hand drawing of how I believe everything is connected. ;0)


PSS. After reading many of the posts about these batteries, I'm thinking it might be better to just purchase a new battery. Is there a possibility to damage the new battery? Do you believe I've ruled out problems with the other electronics? Can I go to a higher voltage without changing anything else?

 

[amberwolf]

amber wolf, Ok I did as you asked and yes the battery meter is working. So assuming that my next step is to check the battery (the individual cells) how do I get it out of the case and more importantly how to do this safely? I'm a little apprehensive working with these battery types. I'm assuming it's Lithium-ion! The battery itself appears to be glued into the case. I don't seem to be able to slide it out of the case. When I look down he case from one end to the other. I can't see completely from one end to the other all the way around the battery!

If the batteries are glued into the case, then the only way to test the cells is to measure at the BMS connectors, preferably without disconnecting from the BMS. Can you see the BMS itself, and it's wiring / connectors? If so, take good clear well-lit pictures of it to post here and we can see if there is a way to reach them to test. You may not be able to repair the pack if you can't get to the cells, though, depending on what is wrong.

PSS. After reading many of the posts about these batteries, I'm thinking it might be better to just purchase a new battery. Is there a possibility to damage the new battery? Do you believe I've ruled out problems with the other electronics? Can I go to a higher voltage without changing anything else?

I would stay with the same voltage pack if you dont' know what all the parts on the bike are designed to take. For instance, any battery meter will read fuller than it really is, and any safety cutoffs intended to prevent damage to the battery won't work on a higher voltage battery. If parts aren't able to handle the higher voltage, they may fail immediately or later on.

Just make sure the new battery is rated for the same or higher A (amps, not Ah) so it can still run the bike correctly. It also needs to have the same or higher Ah (not A) so you get the same range out of it.


Note that if we don't know that the battery itself has a problem, a new battery may not fix it--if something on the bike (controller problem, etc) caused the battery to shutdown, it may do the same to the new one. It's unlikely, but a possibility.