Variable battery charger?

Can anyone recommend a battery charger that would allow me to see how much the battery is charged rather than just a red/green light saying that it's 100%? I've got a 48V 10.4 battery on a 500W motor. Thank you

Put one of these in your charge lead, then you'll know precisely - much cheaper than a new charger

https://www.ebay.co.uk/itm/Precision-rc-130A-watt-meter-and-power-analyzer-LCD-gt-power-60V-UQRDUK-DS/392753053972?hash=item5b71e80114:g:p3UAAOSwHwNbjOIz

Put one of these in your charge lead, then you'll know precisely - much cheaper than a new charger

https://www.ebay.co.uk/itm/Precision-rc-130A-watt-meter-and-power-analyzer-LCD-gt-power-60V-UQRDUK-DS/392753053972?hash=item5b71e80114:g:p3UAAOSwHwNbjOIz

Thanks a lot! I never knew they existed :-)

You can put them between your battery and controller too so that you can see exactly how much battery you've used and how much you have left. It's very accurate, not like those stupid estimating systems you get with Bosch type systems. I used to have one on all my bikes because I was interested in comparisons and efficiencies. It was a great learning experience and it gave me a good understanding of how the power in various ebike systems works.

It's very accurate, not like those stupid estimating systems you get with Bosch type systems.

Basically I agree. One detail: I think (but you may well be able to correct me) that the Bosch system has a similar device built in; and that the system does know the state of charge quite accurately. The silly remaining range estimate is based on charge remaining (fairly accurate) and rate of use (rubbish). The stupid result is because the way it computes rate of use is based on much too short a history.

 

It could give a sensible remaining charge if it were more sensibly programmed.

Basically I agree. One detail: I think (but you may well be able to correct me) that the Bosch system has a similar device built in; and that the system does know the state of charge quite accurately. The silly remaining range estimate is based on charge remaining (fairly accurate) and rate of use (rubbish). The stupid result is because the way it computes rate of use is based on much too short a history.

 

It could give a sensible remaining charge if it were more sensibly programmed.

I was going to say exactly that, which makes it even more stupid, but I didn't feel like typing it all out. Thanks for saving me.

I have to agree , the system has far better knowledge than it shows , and is based on far too short a history , go up a hill your range is halved , coast down one , its doubled , but the BMS will cut out even if you know you can get home , just 'cos of the last hill , one of the irritations of Bosch . Still works extremely well for 99% of the time , purely IMHO .

[mention=4809]vfr400[/mention] -I'd not seen one of those watt meter devices before - a question if I may?

 

I can see that the WATT reading is a simple calculation based on the current being drawn and the battery voltage at the time, but can you tell me to what use the Amp Hour reading is put to please?- apologies if this is a dumb question. Thanks

 

The amp hour is the the cumulative use of current. So 1 amp for 2 hours is 2 amp hours, so is 2 amps for 1 hour. Of course your current is not steady for an hour at a time, but it's clever enough to add up all the little fragments.

 

It's one of the most useful readings because you get an idea how much you've used and thus how empty your battery is. The battery capacity is often quoted in amp hours; if not it will be quoted in watt hours, and the amp hours is the watt hours divided by the nominal voltage.

Ah is the fuel gauge. If you run your battery down from full, you'll see how many Ah you have in your battery. That takes into consideration your riding style as well as any measurement errors, and it will be fairly constant. For each new ride with a charged battery, the meter will show how many Ah you've used, so you can compare that with how many you have, like when it said the battery contains 12.2 Ah and shows that you've used 6.1Ah, you know you're half way down. Other similar meters have Watt-hours (Wh), which is slightly better.

 

You can modify the meters by removing the shunts and mounting them in the battery wire so that you can mount the meter on your dashboard.

 

Some info in this thread I did back in 2014.

https://www.pedelecs.co.uk/forum/threads/the-best-value-wattmeter.16869/

 

lots of photos here:

https://app.photobucket.com/u/d8veh/a/956f0711-e923-46a8-8152-26c4c49386ac

As an asside here...I've got one of these Watt Meters. Is the "Vm" value the mean voltage value used to calculate the number of Watt hours?

As an asside here...I've got one of these Watt Meters. Is the "Vm" value the mean voltage value used to calculate the number of Watt hours?

Minimum voltage.

As it knows the actual voltage at any time it should use that to calculate watt hours. It will vary with time as does current; the voltage variation won't be nearly as much as the current one.

As it knows the actual voltage at any time it should use that to calculate watt hours. It will vary with time as does current; the voltage variation won't be nearly as much as the current one.

Voltage is not a good measure of capacity because it doesn't go down linearly, and it also varies with current.

Minimum voltage.

 

Are you sure about that? I used to think it was minimum voltage, but I've often seen the voltage dip under load below the stated value "Vm" given at the end of the ride.

Are you sure about that? I used to think it was minimum voltage, but I've often seen the voltage dip under load below the stated value "Vm" given at the end of the ride.

These things are made for the RC hobby, where they use lipos. The minimum voltage is important. Show which one you have.

Voltage is not a good measure of capacity because it doesn't go down linearly, and it also varies with current.

Indeed, voltage isn't a good measure of capacity, but it is needed for correct calculation of wH provided by the battery.

 

Because of voltage drop etc I suspect that aH used is better for measuring remaining capacity than wH. Someone with better knowledge of batteries can clarify; but ??? if you use a battery under heavy load then light load the aH used will be similar in each case, but the wH will be quite a bit lower in the heavy load case???

Indeed, voltage isn't a good measure of capacity, but it is needed for correct calculation of wH provided by the battery.

 

Because of voltage drop etc I suspect that aH used is better for measuring remaining capacity than wH. Someone with better knowledge of batteries can clarify; but ??? if you use a battery under heavy load then light load the aH used will be similar in each case, but the wH will be quite a bit lower in the heavy load case???

That's not right. I think you have the right idea, but it's the wrong way round. Watt-hours are a measure of how much charge is in the battery. Watt-hours are a constant size. You can take them out quickly or slowly. If you have a 400Wh battery and take out 350Wh, you have 50Wh left, regardless of how fast or slow you took them. It's amp-hours that are not precise because you can have big ones or small ones. The energy in an amp-hour at the start of your ride at say a constant 5 amps would be 40x5 =200Wh, but at the end of your ride, it would be 35x5 =175Wh.

 

That's the principle, but it's not the whole story, which is why I said you need to do a complete battery cycle with your typical riding style to find out how many watt-hours your battery actually gives for your rides. A battery will give a different number of watt-hours depending on how hard you drive it, so if one day, you go everywhere at maximum power and the next you go on eco, there will be a difference. No prediction system can cope with that, but you will soon see and learn the difference by observing the wattmeter, so you can make the correct approximate calculation in your head. It sounds difficult, but when you have the wattmeter on your handlebars, you soon figure everything out.