How Much Battery Power Do I Need?

[rbscebu]

I live on a relatively flat island with a circumference of about 26km (16 miles). A typical daily ride for me would be at most 20km (all sealed roads) with about 2km of 1% assent, 2km of 1% decent and the rest on the flat. Average speed would be about 15kph (9.4mph). Due to traffic congestion, my maximum speed would be about 30kph (18.8mph).

My bike is fitted with a 48V 1000W ungeared brushless rear hub motor on a 26" wheel with 480rpm maximum. The motor controller has a current limit of 30A. The bike is fitted with a 5-magnet PAS (although I don't know yet how this intergrates with powering the bike) and thumb throttle. There is no provision for changing PAS mode. All up bike mass (including rider) will be about 150kg (330 lb). Assume that there is no recharging facilities during a ride.

I am looking to buy 4 x 12VDC sealed acid-glass-mat (AGM) deep-cycle batteries to power the bike. My problem is to determine what Ahr rating to get.

I need to keep my expenses down and can purchase:

12V 16Ahr @ USD25 each
12V 20Ahr @ USD40 each
12V 22Ahr @ USD43 each

Of course I would prefer the 16Ahr batteries but will they leave me will short of the power that I may need?

 

[JRA]

You will need 4 of those to get 48v. Run your controller at me more than 15. Get a 48v 10ah Li Ion battery from somewhere.

 

[rbscebu]

I understand that I will need 4 x 12V batteries.

What do you mean "Run your controller at me more than 15."?

Unfortunately the cost of Li Ion batteries are beyond my available budget.

 

[indianajo]

When putting batteries in series the Amp Hour rating stays at the minimum AH of the stack. So four 12 v 16 AH batteries should get you 48v @ 16 AH
16 AH @ 48 v should get you 50+ miles at those speeds.
I don't know if the lead acid batteries have a discharge rate that will support 30 A, but you should rarely be using that much current on a flat island. The cheap controllers do tend to accelerate at maximum power from zero to the programmed PAS speed.
The charge voltage for a 12 v lead acid battery is about 14.4 v, so to not disassemble your battery stack for charging you would need a 48 v charger stopping at 57.6 v. You won't be able to find such a device. 13 cell Li Ion stops at 54.6 and 14 cell LiFePo4 stops at 58.8. The trouble with e-bay/amazon "48 v " chargers is that the stop voltage is not even specified in the listing. You have to buy it to see the value. I tried to adjust my 58.8 charger down to 54.6 to fit my new battery and found the lowest value turning the pot would adjust it to was 58.0.
In Li Ion you could get away with an 8 AH battery for those short rides, but those are about $300.

 

[Bruce Arnold]

I'm with Indianajo. Get the 16 Ah batteries, you will have plenty of power.

But don't sweat the charger deal. I use 12 V SLAs for a lot of my portable ham radio gear. I use a Noco Genius battery charger. These things are very smart. They both charge and maintain batteries. You would have to disconnect the batteries so they aren't in series, but with the right connectors -- I like Andersen PowerPoles -- that is not a problem. Re-connect them in parallel and you can charge them all at once, because then the system is at 12 V instead of 48.

 

[JRA]

You are going to need a trailer to haul 4 12v 16ah batteries around

 

[rbscebu]

Thank you to all for the advice.

I understand about connecting batteries is series, 4 x 12V 16Ahr = 48V 16Ahr.

I have decided to buy the 4 x 12V 16Ahr batteries (4.3kg or 9.5 lb each) for USD97 total incl. delivery.

I already have a 48V 20Ahr charger to use with these batteries.



Each battery is 150mm x 98mm x 98mm (5.9" x 3.9" x 3.9").

 

[AHicks]

Curious on your impressions after riding it for a while?