Charging to X% - What about rigging up a voltmeter with alarm?

[Manc44]

In an ideal world we'd all buy that Satiator charger, but it's expensive.

I had an idea... why can't you just have a voltmeter with an LED readout of the voltage, that has an alarm you can set to go off when a certain voltage is reached, that has an XT60 plug (or any you want) on it?

Do these things exist?

I also thought (but I know these won't exist lol) imagine if it could send you an SMS message when the voltage is reached. That would be useful if you had your battery charging in the garage 2 rooms away in a bulletproof tin and can't hear the alarm... on your voltmeter thing that doesn't exist.

Surely there's a big demand for such a simple thing, not with SMS, I mean the first thing I mentioned.

 

[vfr400]

Why do you want to charge to X% when the battery is designed to be charged to 100% and you get less power and range by not fully charging it, and you shorten the battery life.

The Satiator is for batteries that don't use top balancing, but yours does.

 

[Manc44]

Because of all this 80% talk lol

 

[StuartsProjects]

Do these things exist?

Sure, take a look on eBay, Aliexpress etc..........

 

[mike killay]

Because of all this 80% talk lol

I am not too sure that this 80% is out dated now.
I always charge to 100% (part of the reason being to ensure that the battery balances itself which it won't do with a partial charge)
My oldest battery, still giving about 70% of new condition is now 10 years old. It is my spare and lives months on end in the shed, always topped up to 100% every few months.

 

[vfr400]

Because of all this 80% talk lol

A lithium cell pack will last longer if you only charge it to 80% AND keep it balanced. The problem is that with your ebike battery, you can't have both.

The idea of charging to 80% is based on a study that Battery University did on individual lithium cells. It was done a long time ago and was about how to manage them. Unfortunately, your battery has been provided with a management system that tries to give the best mix of all performance characteristics, not just long life.

If you want to charge to 80%, you must remove the BMS and install a different one that allows manual balancing or balances at one or more states of charge below 80%.

Bear in mind that battery technology has moved on a lot since that BU article, and it's conclusions might not still be valid.

 

[Manc44]

OK cheers. I thought the BMS balanced the cells regardless of the amount it's charged. This is why I thought I could stop charging it at 80% or 90% and it would end up balanced, regardless of whether a charger is plugged in or not.

 

[mike killay]

Lots of things now have lithium cells and all are normally kept full.
My laptop, tablet, earphones, mobile, vapes, razor, Roomba robot hoover, Shark lightweight hoover, camera.

 

[Manc44]

I guess. There's days I have my ecig plugged into the USB on my PC charging but I'm vaping on it all day at the same time it's charging.

AW IMR (18650)
Claimed mAh when new: 2200
mAh now: 1343
mAh loss: 39%
Days used: 1409
Cycles: Approx. 450

Sony VTC6 Red Murata (18650)
Claimed mAh when new: 3000
mAh now: 1868
mAh loss: 38%
Days used: 613
Cycles: Approx. 150

Not sure what those red Murata are, but they were bought from nkon.nl and have only been charged 150 to 200 times, yet have lost 38% of their capacity. I have no idea what the actual mAh was when they were new. The AW IMR have been charged and discharged 3 times more yet have "only" lost about the same % of capacity.

 

[vfr400]

I guess. There's days I have my ecig plugged into the USB on my PC charging but I'm vaping on it all day at the same time it's charging.

AW IMR (18650)
Claimed mAh when new: 2200
mAh now: 1343
mAh loss: 39%
Days used: 1409
Cycles: Approx. 450

Sony VTC6 Red Murata (18650)
Claimed mAh when new: 3000
mAh now: 1868
mAh loss: 38%
Days used: 613
Cycles: Approx. 150

Not sure what those red Murata are, but they were bought from nkon.nl and have only been charged 150 to 200 times, yet have lost 38% of their capacity. I have no idea what the actual mAh was when they were new. The AW IMR have been charged and discharged 3 times more yet have "only" lost about the same % of capacity.

The manufacturers specify the life of their cells with the number of charge cycles; however, that's at relatively low current. Assuming that your vape has the normal massive current, the cells won't give you anywhere near what the apecification is.

You'll be OK doing life cycle tests at 80% because there's no BMS, though I doubt that you'll see much difference.

 

[egroover]

When you build or convert a bike you stop worrying about this stuff. You buy a high capacity quality celled battery from Aliexpress for a quarter of the price of the equivalent replacement cost of a Bosch, Shimano etc battery and use it and fully charge it every time. 5 years later when the range has dropped off, you shell out another £200 for the replacement. Cheap, stress free ebiking

 

[Nealh]

OK cheers. I thought the BMS balanced the cells regardless of the amount it's charged. This is why I thought I could stop charging it at 80% or 90% and it would end up balanced, regardless of whether a charger is plugged in or not.

Most BMS are top end balancing so typically 4.15 - 42v per cell.
With a smart BT or Uart BMS one can set the balance to any voltage.
Problem is with 80% is you loose a lot of range and power, 90% or 4.1v may be a better solution if one had a smart BMS as there is little usable capacity in the last 10%.

 

[Nealh]

I guess. There's days I have my ecig plugged into the USB on my PC charging but I'm vaping on it all day at the same time it's charging.

AW IMR (18650)
Claimed mAh when new: 2200
mAh now: 1343
mAh loss: 39%
Days used: 1409
Cycles: Approx. 450

Sony VTC6 Red Murata (18650)
Claimed mAh when new: 3000
mAh now: 1868
mAh loss: 38%
Days used: 613
Cycles: Approx. 150

Not sure what those red Murata are, but they were bought from nkon.nl and have only been charged 150 to 200 times, yet have lost 38% of their capacity. I have no idea what the actual mAh was when they were new. The AW IMR have been charged and discharged 3 times more yet have "only" lost about the same % of capacity.

Sony no longer make cells and they are made under licence my Murata who bought the business, hence the name.

 

[Sturmey]

Do these things exist?
Surely there's a big demand for such a simple thing, ..........

There is a simple known method. This involves putting 1 or 2 or more suitable diodes in series with the charger output. This lowers the output voltage marginally by about .5 - .7 volt per diode (depending). (A side effect is that it delays the end of charging/red light going off but it works) A switch can be fitted to short out/bypass diodes and restore normal charging.
I tend to treat my batteries like a good 'pint of Guinness', filling them to about three quarter level initially and topping them up shortly before a long ride.

 

[Nealh]

I tend to treat my batteries like a good 'pint of Guinness', filling them to about three quarter level initially and topping them up shortly before a long ride.

It is what I do, if I need to nip out for an errand or a 10/15 miler then the battery has plenty in it.

 

[Manc44]

That's the best solution I've seen yet.
If there's a problem

 

[KeithMac]

I just charge them up, my GTECH managed 6 years constant use like that so in my book that's all you can ask from a battery.

Same with phone, cordless tools ect, all charged to full and never had a problem. My DeWalt Lithium drill is knocking on 15 years or more now and still works fine..