Battery

[cyclenut1952]

I realise this might seem pointless to most but, I have a 10.2 amp battery with 34 volts remaining, my charger is 2amp. I know for every hour it puts 2amp back in the battery so if I didn’t want to fully charge it say to 39v, from voltage given how long do I charge it for? Thanks

 

[Andy-Mat]

I realise this might seem pointless to most but, I have a 10.2 amp battery with 34 volts remaining, my charger is 2amp. I know for every hour it puts 2amp back in the battery so if I didn’t want to fully charge it say to 39v, from voltage given how long do I charge it for? Thanks

Your question is valid, and the easiest way to probably achieve what you require, is to measure the actual voltage. Charge say for 30 minutes and measure the voltage again.
This will allow you to roughly see what length of charge puts how many extra volts into the battery.
For when I need a full charge timing, I simply place the battery say at 30 volts, charge to full (42 volts on a 36 volt Li-ion Battery), checking frequently for the charge LED to change to green, and note the length of time it took.
I then charge, with an old fashioned 24 hour timer inserted in the mains lead, to COMPLETELY stop the charge (reoving the mains voltage completely) at the roughly calculated time to maximum charge, plus say 10 minutes or so, just to make sure it is really full.
To do that, the timer's wiring is slightly modified, so that the synchronous motor in the timer, is switched off when the end time is reached, thereby preventing the timer charging again, 24 hours later!
Totally simple and VERY cheap!
The timer can also be useful if only a partial charge is actually needed, for battery storage purposes for example, setting a roughly calculated shorter time! Naturally, always check that the end result is achieved that you wish!
The main reason for using the timer, is to prevent even micro amps, of continuing charge, which many of the cheaper chargers do. That is simply not good for the long term life of the battery. This is well known by industry battery professionals.
There may be other simpler methods that someone else can post here!
But never ever believe that a charger switches off completely, unless it has been fully checked by an expert that it does!
I hope this helps you further.
Andy

 

[mike killay]

Your question is valid, and the easiest way to probably achieve what you require, is to measure the actual voltage. Charge say for 30 minutes and measure the voltage again.
This will allow you to roughly see what length of charge puts how many extra volts into the battery.
For when I need a full charge timing, I simply place the battery say at 30 volts, charge to full (42 volts on a 36 volt Li-ion Battery), checking frequently for the charge LED to change to green, and note the length of time it took.
I then charge, with an old fashioned 24 hour timer inserted in the mains lead, to COMPLETELY stop the charge (reoving the mains voltage completely) at the roughly calculated time to maximum charge, plus say 10 minutes or so, just to make sure it is really full.
To do that, the timer's wiring is slightly modified, so that the synchronous motor in the timer, is switched off when the end time is reached, thereby preventing the timer charging again, 24 hours later!
Totally simple and VERY cheap!
The timer can also be useful if only a partial charge is actually needed, for battery storage purposes for example, setting a roughly calculated shorter time! Naturally, always check that the end result is achieved that you wish!
The main reason for using the timer, is to prevent even micro amps, of continuing charge, which many of the cheaper chargers do. That is simply not good for the long term life of the battery. This is well known by industry battery professionals.
There may be other simpler methods that someone else can post here!
But never ever believe that a charger switches off completely, unless it has been fully checked by an expert that it does!
I hope this helps you further.
Andy

Is this claim true?
As far as I can see, it is the BMS in the battery, not the charger that switches off.

 

[cyclenut1952]

Hi Andy, thanks for replying very much appreciated. As a novice to ebikes this info is great, I always unplug charger from battery and charger from wall socket.
If I could ask one more question, the charger only gives out 41.6v is that ok
Many thanks Brian

 

[Deleted member 25121]

I realise this might seem pointless to most but, I have a 10.2 amp battery with 34 volts remaining, my charger is 2amp. I know for every hour it puts 2amp back in the battery so if I didn’t want to fully charge it say to 39v, from voltage given how long do I charge it for? Thanks

With modern technology battery packs and chargers you don't need to be too concerned about damaging the battery, as Mike Killay points out the pack will contain a Battery Management System (BMS) that looks after the charging and discharging the battery cells.
You should be able to see from either the charger, the battery pack and/or the handlebar display the percentage charge of the battery, if the charger was left on for another 8 hours say it's not going to cause any significant damage. Best not to leave it on all night though and best not to leave a battery fully charged for longer than a week or 2.

One or 2 people on here would recommend otherwise but they're not familiar with modern battery technologies.

 

[Deleted member 25121]

If I could ask one more question, the charger only gives out 41.6v is that ok

41.6V is fine.

 

[Andy-Mat]

Hi Andy, thanks for replying very much appreciated. As a novice to ebikes this info is great, I always unplug charger from battery and charger from wall socket.
If I could ask one more question, the charger only gives out 41.6v is that ok
Many thanks Brian

That is most likely to be a slight error of your voltmeter.
If the voltmeter is accurate (compare it to a known accurate meter), it is on the "safe side" of charging. You lose only a very small, unimportant really, percentage of the capacity.
regards
Andy

 

[mike killay]

Agreed,
I have one volt meter, 4 batteries and 4 chargers.
They all read 41.6 volt, so I guess that the meter is reading slightly low

 

[cyclenut1952]

Thanks to all very interesting

 

[Deleted member 25121]

Ebike battery packs aren't high accuracy 42.000V voltage standards and the 42V charged voltage should be considered as a nominal value only.

41.6V is less than 1% lower than 42.0V after all.

 

[Andy-Mat]

Agreed,
I have one volt meter, 4 batteries and 4 chargers.
They all read 41.6 volt, so I guess that the meter is reading slightly low

I agree, but as you now know that, its not a problem anymore.
I would bet that a fully accurate meter would read 42 volts!
Regards
Andy

 

[soundwave]

if you get a cheap meter you can calibrate them they will have a pot inside that you can adjust a new fully charged 18650 will do.

if you want a decent meter buy a fluke

 

[Deleted member 25121]

I would bet that a fully accurate meter would read 42 volts!

To what tolerance, +/-1mV, +/-10mV, +/-100mV??

A 36v battery pack ican be thought of as being made up of groups of 10*18650 cells in series. These cells have a typical fully charged voltage of 4.20V +/-50mV each, so 10 of these in series would give 42.0V +/-500mV
ie a nominal voltage of somewhere between 41.5V and 42.5V in total.

There's nothing in the 18650's chemistry to say that its fully charged voltage should be exactly 42.000V. Also, the "fully charged" voltage will depend on many things including the cell design & chemistry, the charging current and charging methodology, the temperature during charging, the way the charger maintains the fully charged state, the age of the cell, has the cell been used with high current loads, with low current loads, at high operating temperature, at low operating temperature, has it been stored at a low temperature, was it fully charged when stored at a low temperature etc etc etc.

Welcome to the world of physics and engineering vs "I would bet that a fully accurate meter would read 42 volts!"

This link may give you a clue as to some of the complexities involved:

Charging Lithium-Ion Batteries

Review simple guidelines for charging Lithium-based batteries and prolong battery life such as; a portable device should be turned off while charging and more.

batteryuniversity.com

 

[Andy-Mat]

To what tolerance, +/-1mV, +/-10mV, +/-100mV??

A 36v battery pack ican be thought of as being made up of groups of 10*18650 cells in series. These cells have a typical fully charged voltage of 4.20V +/-50mV each, so 10 of these in series would give 42.0V +/-500mV
ie a nominal voltage of somewhere between 41.5V and 42.5V in total.

There's nothing in the 18650's chemistry to say that its fully charged voltage should be exactly 42.000V. Also, the "fully charged" voltage will depend on many things including the cell design & chemistry, the charging current and charging methodology, the temperature during charging, the way the charger maintains the fully charged state, the age of the cell, has the cell been used with high current loads, with low current loads, at high operating temperature, at low operating temperature, has it been stored at a low temperature, was it fully charged when stored at a low temperature etc etc etc.

Welcome to the world of physics and engineering vs "I would bet that a fully accurate meter would read 42 volts!"

This link may give you a clue as to some of the complexities involved:

Charging Lithium-Ion Batteries

Review simple guidelines for charging Lithium-based batteries and prolong battery life such as; a portable device should be turned off while charging and more.

batteryuniversity.com

You are searching for a problem that really does not exist, unless of course a meter is VERY inaccurate.
I have two good meters, one is a Fluke, I forget the name of the other one, but both of them show 42.00 on either of my batteries....but its also a function of both charger and BMS!
Maybe I am "spoilt" in having accurate meters and good chargers etc., never really thought much about it as for me inaccurate test equipment is a waste of my time and my money.....
I also possess two cheapo meters, both of which also happen to show 42 volts, (possibly more by accident than design!) though they are only for "lending out" to friends.
As those without a meter do not get lent either of my good ones.....
But I do not lend out tools of any type, as too much has gone missing over the years!
But I do "lend out" my technical knowledge as help!
Remember, the final accuracy of a meter has several main factors, the actual quality of the build, the way the algorithm "rounds off" the value displayed and of course the number of decimal places displayed.
I was keeping things simple for the people here who are not electrically/electronically trained....
"K.I.S.S!"
Andy

 

[Nealh]

I was keeping things simple for the people here who are not electrically/electronically trained....
"K.I.S.S!"
Andy

That might be a first then.

 

[Deleted member 25121]

You are searching for a problem that really does not exist, unless of course a meter is VERY inaccurate.
I have two good meters, one is a Fluke, I forget the name of the other one, but both of them show 42.00 on either of my batteries....but its also a function of both charger and BMS!
Maybe I am "spoilt" in having accurate meters and good chargers etc., never really thought much about it as for me inaccurate test equipment is a waste of my time and my money.....
I also possess two cheapo meters, both of which also happen to show 42 volts, (possibly more by accident than design!) though they are only for "lending out" to friends.
As those without a meter do not get lent either of my good ones.....
But I do not lend out tools of any type, as too much has gone missing over the years!
But I do "lend out" my technical knowledge as help!
Remember, the final accuracy of a meter has several main factors, the actual quality of the build, the way the algorithm "rounds off" the value displayed and of course the number of decimal places displayed.
I was keeping things simple for the people here who are not electrically/electronically trained....
"K.I.S.S!"
Andy

You really don't have a clue about accuracy and tolerances do you..

 

[Andy-Mat]

You really don't have a clue about accuracy and tolerances do you..

Actually I do, but it is simply not needed in this case to be accurate to the last micro volt!

 

[Sturmey]

I have two different multimeters, both function well but would be relatively cheap.e.g 10 to 20 euro price range. The minimum accuracy quoted is the same for both on the voltage scale, which is (+/- .5%) + 1digit (least significant digit) I think this figure is typical on budget multimeters.
So reading on the 200V scale, at 42volts, the tolerance would be .21v +.1 =.31volts. i.e An error of (point3) or .3 volt or even possibly .4v would be within the tolerances or put another way, a reading 41.7 - 42.3 or possibly 41.6-42.4, would be within the quoted tolerance.
More accurate meters are generally more expensive.

 

[Deleted member 25121]

Actually I do, but it is simply not needed in this case to be accurate to the last micro volt!

You're the one talking of microvolts (please note the correct spelling), not me.

As mentioned before, the charged voltage of a 38V pack can be between between 41.5V and 42.5V, ie 42.0V +/- 0.5V ie 42V +/-1.2%.
Strumey's cheapish DVM measures 42V with an accuracy of +/- 0.3V so it could indicate anything between 41.2V and 42.8V.

So we're talking 100's of millivolts here (note the correct spelling), not microvolts (note the correct spelling).

 

[Deleted member 25121]

I have two different multimeters, both function well but would be relatively cheap.e.g 10 to 20 euro price range. The minimum accuracy quoted is the same for both on the voltage scale, which is (+/- .5%) + 1digit (least significant digit) I think this figure is typical on budget multimeters.
So reading on the 200V scale, at 42volts, the tolerance would be .21v +.1 =.31volts. i.e An error of (point3) or .3 volt or even possibly .4v would be within the tolerances or put another way, a reading 41.7 - 42.3 or possibly 41.6-42.4, would be within the quoted tolerance.
More accurate meters are generally more expensive.

Your multimeter's specs are actually very good, possibly over optimistic specs from the Far East. As an example, the Fluke 115 Handheld Digital Multimeter available from RS for £247.00 + VAT including UKAS calibration has an accuracy spec of +/-(2% of reading + 3 counts) on its 60V range which has a resolution of 0.01V

So it can measure 42V to within +/- 0.87V, ie +/- 2.1%. And that's a £247 + VAT instrument from a reputable US test and measurement equipment supplier.

https://docs.rs-online.com/b473/0900766b80802a0c.pdf

Claims that people can measure 42.00V with absolute accuracy are clearly far fetched.