KWhrs to charge a 36v 17ah battery

[point5clue]

Hi team,
I don't necc. have a problem, but I'm intrigued as to whether my suspiciously cheap 17ah battery really is such.

I thought I'd plug in my energy meter to see how much it uses. When it started it was only drawing about 1A and once it had finished (actaully 12hrs later) it has drawn 0.5 KWhrs (not exactly granular even if it was accurate).

I'm wondering if anyone else has done similar to compare it with ?

Oh, I should say starting point for the charge was after a long ride and voltage showing was 35.5 so pretty low if I understand correctly.

 

[Woosh]

that result does not mean much, only that you have charged your battery roughly 450WH,
The capacity of a 17AH battery is 612WH, 450WH is roughly 74%. You battery could have 24% charge before charging.
To be sure, measure that voltage of the battery before charging then post the result.

 

[cyclebuddy]

0.5 kilo-watt-hours = 500 watts / 36 volts = 13.88Ah. It's hard to know the true capacity of any battery unless your drain it totally before charging/measuring (at least to where the BMS cuts power).

Ideally, you would need to measure the discharge rather than the charge, because some energy is wasted in heat. What you really need to know is how much energy the battery can put out, not what you necessarily put in.

Just my two cents.

 

[point5clue]

Thanks - its simpler than I assumed - a watt is a watt even though its supplied by 240v AC ?

The starting voltage was 35.5.

My take - its close enough that it not just a few flat sainsburys batteries and some sand - really what matters are the journeys and I've been able to ride 36 miles on PAS 4 without running out, so will do for now.

 

[Woosh]

The starting voltage was 35.5.

then your battery is a good 17AH.
35.5V corresponds to 35% remaining charge.

 

[cyclebuddy]

Thanks - its simpler than I assumed - a watt is a watt even though its supplied by 240v AC ?

Now I'm confused... You used a DC watt-meter to measure the energy being output from the charger into the battery, or a 240v AC watt-meter to measure the 240v energy the charger consumed while charging your battery?

If I misunderstood and you meant the latter, then your measurement tells you nothing. There is no direct correlation between what a 240v AC mains powered charger consumes and what it generates in DC because they have different efficiency levels.

Ideally, you need to fully charge your battery, rig a fixed load, and measure the full DC output/discharge of your battery. That tells you exactly what your battery can deliver.

 

[Deleted member 4366]

You need to allow for the efficiency of conversion from 250v to 42v, which is probably something around 90%, so 500wh consumed is about 450wh into the battery

 

[cyclebuddy]

Without trying to hijack this thread, let me throw this out there to see if someone has more up-to-date knowledge than I:

Battery charger efficiency comes under EU regulations, and was introduced because many SMPS battery chargers were in the old days hideously inefficient (as low as 50%). The efficiency standards are continually being improved, and the standard has latterly been upgraded from level 5 (about 85% efficient) to level 6 in 2016. This should be marked on all battery chargers with a roman numeral in a circle (i.e. V for efficiency level 5, VI for 6).

But as I understand it, any charger intended for charging a battery pack to be used to power a motor propelled device (car, lawnmower, e-bike) is (or certainly was) EXEMPT from these EU regulations.

My laptop, tablet, phone chargers ALL have the energy efficiency mark. But NONE of my three e-bike chargers do: Judging from the excessive heat they generate, I’m guessing my e-bike chargers really aren’t that efficient – and certainly not up to the 85% level V or new current level VI. So using AC input energy to estimate DC output is pretty unreliable in my view.

Does anyone know if this EU energy efficiency exemption still applies? And if not, why don’t my e-bike chargers have any efficiency level marked on them? The manufacturer’s website makes no efficiency claims either... which is strange if their chargers were efficient and did meet that standard (whether required to or not).

Mmmm.

 

[anotherkiwi]

Without trying to hijack this thread, let me throw this out there to see if someone has more up-to-date knowledge than I:

Battery charger efficiency comes under EU regulations, and was introduced because many SMPS battery chargers were in the old days hideously inefficient (as low as 50%). The efficiency standards are continually being improved, and the standard has latterly been upgraded from level 5 (about 85% efficient) to level 6 in 2016. This should be marked on all battery chargers with a roman numeral in a circle (i.e. V for efficiency level 5, VI for 6).

But as I understand it, any charger intended for charging a battery pack to be used to power a motor propelled device (car, lawnmower, e-bike) is (or certainly was) EXEMPT from these EU regulations.

My laptop, tablet, phone chargers ALL have the energy efficiency mark. But NONE of my three e-bike chargers do: Judging from the excessive heat they generate, I’m guessing my e-bike chargers really aren’t that efficient – and certainly not up to the 85% level V or new current level VI. So using AC input energy to estimate DC output is pretty unreliable in my view.

Does anyone know if this EU energy efficiency exemption still applies? And if not, why don’t my e-bike chargers have any efficiency level marked on them? The manufacturer’s website makes no efficiency claims either... which is strange if their chargers were efficient and did meet that standard (whether required to or not).

Mmmm.

Covered by:
http://ec.europa.eu/growth/sectors/electrical-engineering/lvd-directive_en

 

[Woosh]

Battery charger efficiency comes under EU regulations, and was introduced because many SMPS battery chargers were in the old days hideously inefficient (as low as 50%). The efficiency standards are continually being improved, and the standard has latterly been upgraded from level 5 (about 85% efficient) to level 6 in 2016.

switch mode chargers have always been very efficient, more so with CPU control. 85% would be their minimum efficiency, 90% is usually the case.
Yo can probably estimate the heat loss by checking the battery's voltage while charging, but as a quick estimate, if you have a 2A charger, at 2A, your power meter should show about 85W consumed by the charger. That's 10% more than the energy that the charger pushes into a 35.5V battery.

 

[cyclebuddy]

Covered by:
http://ec.europa.eu/growth/sectors/electrical-engineering/lvd-directive_en

Err... no. That's the Low Voltage Directive. In Britain, that's covered by BS7671 (I am qualified as an electrician, although I retired a few years ago). What I am questioning here is the current legislation that regulates EFFICIENCY - not the safety - of chargers. Specifically, whether Chargers used for e-bikes are exempt from the directive that demands efficiency level VI.

switch mode chargers have always been very efficient, more so with CPU control. 85% would be their minimum efficiency, 90% is usually the case.
Yo can probably estimate the heat loss by checking the battery's voltage while charging, but as a quick estimate, if you have a 2A charger, at 2A, your power meter should show about 85W consumed by the charger. That's 10% more than the energy that the charger pushes into a 35.5V battery.

Err... again no. SMPS used to be horrendously inefficient, but they were cheap to produce and lightweight (without using large amounts of heavy and expensive copper in their transformer), which is why they became popular. It required legislation to improve that efficiency to better than 85%. But yes, they are far more efficient now. But the question remains... why are e-bike chargers not included in the EU directive to ensure efficiency as all our other home/domestic chargers are?

I will drag out my test equipment and test the actual efficiency of my own e-bike chargers someday.

 

[Woosh]

Err... again no. SMPS used to be horrendously inefficient,

I use these chargers all the time. When the charging is finished, their power consumption drops down to 2W-3W, that is just to show how little wasteful they are. I used to design high power amplifiers for pop bands in my younger years, so am quite aware of progress in switch mode circuits.

 

[cyclebuddy]

When the charging is finished, their power consumption drops down to 2W-3W, that is just to show how little wasteful they are.

As you know, as with many battery chemistries (Lithium, Lead etc), charging works by applying constant /maximum current until peak voltage is reached, and then voltage is maintained and current is progressively reduced (CC/CV). That the energy consumption eventually reduces to 2/3W as the pack becomes fully charged says nothing about how efficiently that 240v AC has been converted to DC... That demand for a highly efficient means of power conversion is what the EU directive covers... except it doesn't seem to apply to e-bike chargers (or car battery chargers either for that matter).

 

[Woosh]

you can gain an insight to the conversion efficiency of the charger by checking the power consumption of your charger as I suggested earlier. The efficiency can be derived from this formula: Yield = battery voltage * 2A / observed power consumption.
eg, if battery voltage = 40V and power consumption 88W then yield = 80W/88W = 90%

 

[Deleted member 4366]

Every ebike charger is different. Some get hot, some don't, some have noisy fans in them, some have small fans and some don't have/need fans at all.

 

[cyclebuddy]

Every ebike charger is different...

That really is my point. And, as there still appears to be no legal requirement for an e-bike charger to operate efficiently as all your other home chargers are, it's best not to assume they are all efficient by default - and certainly not if you have an older e-bike/charger.

 

[Benjahmin]

I have a 4A charger with fan, that came with my Ezee kit, takes 2 hours doesn't get warm at all.
2A fanless charger that came with Panda kit takes 4 hours and gets very hot. Hot enough for me to have put it on an offcut of flashing lead, 'cos it worries me.
Surely the one generating all the heat must be more innefficient?

 

[Woosh]

The charger may produce 7W-10W heat, even a small fan can dissipate that much heat with ease.

 

[MikelBikel]

2A at 42V = 84W, so if its losing 10W, then its efficiency is 10÷84 × 100 = 0.119 × 100 = 11.9%, err Loss. Is that right? (i'm rusty at this, can ya tell?)
Or
Put power meters on mains and dc sides and see what the differ is!
Mikel

 

[Woosh]

2A at 42V = 84W, so if its losing 10W, then its efficiency is 10÷84 × 100 = 0.119 × 100 = 11.9%, err Loss. Is that right? (i'm rusty at this, can ya tell?)
Or
Put power meters on mains and dc sides and see what the differ is!
Mikel

if the charger loses 10W then the power meter should show 40V * 2A + 10W = 90W.
The yield will be 80W/90W = 88%