8Fun Kit Mod to 48V

[Deleted member 4366]

With only the normal battery, the maximum speed is about 15mph. Once you get past 12 mph, the current reduces in a ramp down to zero amps at its maximum no-load speed of about 17mph. At that speed, the motor is still spinning, but virtually no current is drawn, so, in that respect, the faster you go, the further you can go..

When you add the booster pack, the whole power curve moves up the speed range, so that you'll be drawing significant current at 17mph. Now you have to pedal at 20mph to reduce it close to zero, so you're likely to use a lot more wHs, even if you go at the same speed, but you have 30% more battery to compensate. If you use the PAS sensor at level one, it shifts the power curve back down, so you'll get a lot more range.

 

[manalog]

With only the normal battery, the maximum speed is about 15mph. Once you get past 12 mph, the current reduces in a ramp down to zero amps at its maximum no-load speed of about 17mph. At that speed, the motor is still spinning, but virtually no current is drawn, so, in that respect, the faster you go, the further you can go..

When you add the booster pack, the whole power curve moves up the speed range, so that you'll be drawing significant current at 17mph. Now you have to pedal at 20mph to reduce it close to zero, so you're likely to use a lot more wHs, even if you go at the same speed, but you have 30% more battery to compensate. If you use the PAS sensor at level one, it shifts the power curve back down, so you'll get a lot more range.

Thanks d8veh, that explains it.

Now with the Booster pack, what I have noticed is that if the Main Battery pack is not fully charged it seems to take it out on the Booster. Today, on the 3rd 12mile commute my main batt is only 1/4 maybe 1/3 charged as there is only one green light and the booster I charged last night this is the 1st time the voltage dropped below 12V and the cells at around 3.9V. Perhaps I should make my Booster a little beefier and add another 3s2p? Is this an overkill?

 

[Deleted member 4366]

The cells in both batteries are 4,2v fully charged. They soon drop down to 4v when you start riding. They gradually go down to about 3.6v, but then start to descend increasingly more rapidly, so at 3.9v, they've got a long way to go. They're only about 25% of the way down in my reckoning.

 

[manalog]

The cells in both batteries are 4,2v fully charged. They soon drop down to 4v when you start riding. They gradually go down to about 3.6v, but then start to descend increasingly more rapidly, so at 3.9v, they've got a long way to go. They're only about 25% of the way down in my reckoning.

I'm panicking over nothing really as soon as I see anything under 4V I start thinking about recharging. Where can I get a BMS for this? I had a look at BMS battery.com and they have 3 different types. Can I use the original Laptop BMS or is this too optimistic?

Cheers,
G

 

[Deleted member 4366]

The original laptop BMSs are not simple. They often store data about the battery, and can do nasty things like switch off after a certain number of charges or after a certain time,so I wouldn't recommend it. As long as you always fully charge both batteries together, you should never have to worry about your booster pack as long as it has more amp-hours than your main one. You can do a simple test:

Fully charge both batteries;
connect them together and use them for about 25 miles or more (keeping an eye on the booster pack cell voltages; let them settle for 15 minutes or so after the ride;
measure the main pack and divide by ten = individual cell voltage;
measure the cell voltages of the booster pack;
if they're higher than the main pack you can probably forget about monitoring them in the future, but of course, one day you might not charge them properly, so it's always good to have the alarm fitted.

 

[manalog]

The original laptop BMSs are not simple. They often store data about the battery, and can do nasty things like switch off after a certain number of charges or after a certain time,so I wouldn't recommend it. As long as you always fully charge both batteries together, you should never have to worry about your booster pack as long as it has more amp-hours than your main one. You can do a simple test:

Fully charge both batteries;
connect them together and use them for about 25 miles or more (keeping an eye on the booster pack cell voltages; let them settle for 15 minutes or so after the ride;
measure the main pack and divide by ten = individual cell voltage;
measure the cell voltages of the booster pack;
if they're higher than the main pack you can probably forget about monitoring them in the future, but of course, one day you might not charge them properly, so it's always good to have the alarm fitted.

Thanks Dave, will give this a go. I think I have a better idea of what to expect from my Booster Pack. I can only do 3X 12miles commute I can push it to 4X but it means I have to Switch off the motor half way through the 4th commute.
Cheers,
G