Battery Chargers

[robwalley]

Was thinking about a higher amp charger for my 36v 10s5p 14.5A lithium battery.

Not bothered that my current charger is only 2A, requiring overnight usually.

But was thinking of longer day trips requiring a couple of hours charge at a lunchtime watering hole half way round and it would be nice if a 5 or 7a charger was available to cover this.

My questions are:

1. Where can you get these?
2. Does a higher rated charger degrade the battery pack faster?
3. Any issues with fast charging a very recently used pack?

 

[anotherkiwi]

Will the cells in your pack accept higher charging Amps? The popular Samsung 30Q will accept 4 Amps rapid charge. Rapid charge will mean a cell life of about 300 charges compared to up to 600 at 2 Amps.

 

[robwalley]

That's sort of what I'm beginning to read. However my wife's Bosch based Cube has a 4amp charger, in fact all the Bosch bikes are supplied with one although you can get a 2amp cheaper, they don't seem to have lifespan issues do they? If entirely accurate, I'll suck it with a 500ma charger for 29 hours.

 

[Danidl]

Things that degrade battery capacity are . High temperature ,swings from full to empty.
Charging and discharging at high rates are only important in that they raise the temperature because it's an inefficient method of converting the charge state of the chemical.
Remember that most battery packs will have 3 or4 cells in parallel so a 4amp charging is 1Amp per cell.

 

[GLJoe]

That's sort of what I'm beginning to read. However my wife's Bosch based Cube has a 4amp charger, in fact all the Bosch bikes are supplied with one although you can get a 2amp cheaper,

Only the higher end bikes have the 4A charger now, the lower end models all seem to come with the 2A version.
The 2A version is physically smaller, so more attractive for carrying it around with you, but then I don't think the longer charge time will be particularly good if you're stopping somewhere for an hour say and want a quick topup!

 

[Deleted member 4366]

You can charge at 4 amps if you want, but your battery life will probably be shortened a bit. You can get chargers from Ebay or the Chinese sellers, like BMSBattery.

 

[robwalley]

At first it seems to be a major issue to reduce the charges on your battery from 600 (approx) to 400, but I get 50 miles per charge and that's still 20000 miles which in Rob time is 10+ years. Also if you even this out to 500 charges that's around 50 pence per charge (£250), given the electricity is under 10 pence, some of the marketing is a bit off.

I also have a cell charger for 18650's and the smaller 3.7v cells (cannot remember the model) and they have 3 options (0.25, 0.5 and 1.0 amp) to charge so this as Danidl points out this 5 amp charger would only put 1 amp to each set (10s5p) http://www.ebay.co.uk/itm/152471717298.

Anyway the wife has stated very firmly 50 miles per day max, anything else is a hotel and an long charge, so smaller lighter chargers may be the way to go.

 

[Danidl]

At first it seems to be a major issue to reduce the charges on your battery from 600 (approx) to 400, but I get 50 miles per charge and that's still 20000 miles which in Rob time is 10+ years. Also if you even this out to 500 charges that's around 50 pence per charge (£250), given the electricity is under 10 pence, some of the marketing is a bit off.

I also have a cell charger for 18650's and the smaller 3.7v cells (cannot remember the model) and they have 3 options (0.25, 0.5 and 1.0 amp) to charge so this as Danidl points out this 5 amp charger would only put 1 amp to each set (10s5p) http://www.ebay.co.uk/itm/152471717298.

Anyway the wife has stated very firmly 50 miles per day max, anything else is a hotel and an long charge, so smaller lighter chargers may be the way to go.

Your wife seems a sensible wom

At first it seems to be a major issue to reduce the charges on your battery from 600 (approx) to 400, but I get 50 miles per charge and that's still 20000 miles which in Rob time is 10+ years. Also if you even this out to 500 charges that's around 50 pence per charge (£250), given the electricity is under 10 pence, some of the marketing is a bit off.

I also have a cell charger for 18650's and the smaller 3.7v cells (cannot remember the model) and they have 3 options (0.25, 0.5 and 1.0 amp) to charge so this as Danidl points out this 5 amp charger would only put 1 amp to each set (10s5p) http://www.ebay.co.uk/itm/152471717298.

Anyway the wife has stated very firmly 50 miles per day max, anything else is a hotel and an long charge, so smaller lighter chargers may be the way to go.

Your wife seems a sensible woman but the price of charging the battery seems excessive. The battery absorbs 0.5kwhr for a full charge. Electricity costs say 20 pence per kwhr. Even if the charging process was only 75% efficient thats 15 pence

 

[topographer]

Some smartphones claim to charge to 80% very quickly then trickle charge the rest. Can that be done with an ebike battery?

 

[GLJoe]

Some smartphones claim to charge to 80% very quickly then trickle charge the rest. Can that be done with an ebike battery?

Depends on your definition of 'very quickly', but I was under the impression that most of the decent battery charger/systems out there already do that.
??

 

[topographer]

I think I've seen some phone's quoting 80% in 20 mins...but they're small batteries...

 

[GLJoe]

I think I've seen some phone's quoting 80% in 20 mins...but they're small batteries...

The e-bike batteries are a bit slower that that

But I'm fairly sure that chargers from bosch/yamaha/A2B/Stromer etc get up to 80% on a quick charge, then its a slower process to complete to 100%

Thinking of it though, you'd probably need something like a 20A charge to get up to 80% in 20 min. That's a fair chunk of current and I wonder how big the charger would need to be!

 

[Danidl]

The e-bike batteries are a bit slower that that

But I'm fairly sure that chargers from bosch/yamaha/A2B/Stromer etc get up to 80% on a quick charge, then its a slower process to complete to 100%

Thinking of it though, you'd probably need something like a 20A charge to get up to 80% in 20 min. That's a fair chunk of current and I wonder how big the charger would need to be!

The charger would not need to be much bigger. Consider that the power supplies for pcs can range up to a 1kw and are lightweight .
However I don't think that the battery charging scales as simply as that. There is an optimum charge rate and if one increases the applied voltage... the only way of increasing the charging current, the process becomes inefficient. Now the inefficiency ,as a cost might be of little concern, but the energy not transformed in chemical bond's turns into heat and that is a concern. It will certainly reduce the number of possible charging cycles and may create a fire explosive risk

 

[anotherkiwi]

One of the reasons I use LiPo, 58 minutes to fully charge 10 Ah, under 2 hours (a continental lunch break) to charge 20 Ah.

 

[GLJoe]

The charger would not need to be much bigger. Consider that the power supplies for pcs can range up to a 1kw and are lightweight .
However I don't think that the battery charging scales as simply as that. There is an optimum charge rate and if one increases the applied voltage... the only way of increasing the charging current, the process becomes inefficient. Now the inefficiency ,as a cost might be of little concern, but the energy not transformed in chemical bond's turns into heat and that is a concern. It will certainly reduce the number of possible charging cycles and may create a fire explosive risk

The charger might not have to be THAT much bigger, but all the connectors, wiring etc will be. And you just have to look at the difference between the 2A and 4A commercial chargers from people like Bosch to see that there would be a size differential, even when the wiring/current requirements aren't too onerous.
As for the inefficiency/heat etc. Sure, there has to be a problem there. However doesn't something like a Tesla car use pretty much the same 18650 cells as most ebikes? and those can be topped up PDQ with the superchargers.

 

[Danidl]

The charger might not have to be THAT much bigger, but all the connectors, wiring etc will be. And you just have to look at the difference between the 2A and 4A commercial chargers from people like Bosch to see that there would be a size differential, even when the wiring/current requirements aren't too onerous.
As for the inefficiency/heat etc. Sure, there has to be a problem there. However doesn't something like a Tesla car use pretty much the same 18650 cells as most ebikes? and those can be topped up PDQ with the superchargers.

The cross sectional area of copper between 2A and 4A needs is neiglible. Why the 4A charger is larger could very well be due to the vintage of the Bosch factory being used. Its intended to be used at home so making it lighter is not a priority. The thickness of the cables and the insulation on the low voltage side is overkill. The connectors used to charge the Bosch is the same one as used to discharge it into the motor at up to 15 - 20A .. e.g uphill climb on turbo etc so no problem there.
Just because the Tesla cell will use the same mechanical dimensions as other Li Ion cells, does not in itself indicate anything. The Chemistry and the internal fabrication of the cell can be optimised for any combination of low Resistance, for quick discharge and charge, High Capacity for energy storage and high retention for a low internal discharge . In an automotive case, quick charge trumps high capacity as weight is less of a problem. On a bike high capacity may well be preferable

 

[GLJoe]

The cross sectional area of copper between 2A and 4A needs is neiglible.

But we were discussing going 20A+. Then the difference is not negligible.

Why the 4A charger is larger could very well be due to the vintage of the Bosch factory being used.

Or it could be the much simpler and the FAR more likely reason that if you build a higher current power supply - then the physical size gets bigger!

 

[Danidl]

But we were discussing going 20A+. Then the difference is not negligible.

Or it could be the much simpler and the FAR more likely reason that if you build a higher current power supply - then the physical size gets bigger!

Your original posting was a query on why the 4 amp Bosch chargers were significantly heavier and larger than the 2amp ones.
A 20amp 40 volt output is 800 watts. Many of power supplies used in personal computers are at that or higher levels and are not as heavy as the Bosch 4 amp unit. Consider that the majority of the power in such supplies is on the 5v rail. with upwards of 100amps. . With switch mode power supplies the weight of the trafo. , Particularly if switched faster does not scale with power in a simple way


In an old fashioned linear power supply where the mains voltage is reduced by a trafo running at 50hz, then power and weight are simply linked , particularly if there is some control of voltage( regulators ) on the output, which needed heatsinks.

 

[GLJoe]

​

Your original posting was a query on why the 4 amp Bosch chargers were significantly heavier and larger than the 2amp ones.

No it wasn't. Please read posts carefully before replying.

A 20amp 40 volt output is 800 watts. Many of power supplies used in personal computers are at that or higher levels and are not as heavy as the Bosch 4 amp unit
. Consider that the majority of the power in such supplies is on the 5v rail. with upwards of 100amps. . With switch mode power supplies the weight of the trafo. , Particularly if switched faster does not scale with power in a simple way
In an old fashioned linear power supply where the mains voltage is reduced by a trafo running at 50hz, then power and weight are simply linked , particularly if there is some control of voltage( regulators ) on the output, which needed heatsinks.

You can't simply compare a PC power supply with an e-bike charger.
Nobody here except you is mentioning power v size scaling being linked in a simple or linear way.
It is highly unlikely that the Bosch engineers screwed up, and made the original 4A charger hideously over sized for the required specs by choosing the wrong design.
And the reason the 2A charger is smaller is almost certainly because it has to handle less current, and for no other reason other than they MIGHT have compromised on the longevity slightly, but even with that I'm doubtful.

 

[Danidl]

No it wasn't. Please read posts carefully before replying.




You can't simply compare a PC power supply with an e-bike charger.
Nobody here except you is mentioning power v size scaling being linked in a simple or linear way.
It is highly unlikely that the Bosch engineers screwed up, and made the original 4A charger hideously over sized for the required specs by choosing the wrong design.
And the reason the 2A charger is smaller is almost certainly because it has to handle less current, and for no other reason other than they MIGHT have compromised on the longevity slightly, but even with that I'm doubtful.

Hang on and with respect which of us has actually lectured on electronic power supply design? .
The Bosch engineers are not fools and neither of their accountants. When you have an established design in place with supply chains set up etc you only change it for good reason . profitability is best served by long production runs. The 4amp Bosch charger which I have is well suited for its function and is probably made on a long established line. When the requirement for a more portable unit arose they would have gone with a more modern design. Lighter etc but with probably more expensive components. To scale this one from 2 to 4 or 8 amps would have meant slight increases in the weight of the core and more transistors in parallell and revalidation at VDE

The point about pc supplies is that they are in essence exactly the same as the smpsu..actually more complex as they have multiple outputs. So it would easily be within the competence of Bosch to design make and market 1kw smpsu at the same weight as pc ones.