I have a 48 volt system on my motorcycle conversion. Four 12 volt 55 AH 22NF-AGM Lead Acid UB12550 Batteries in series. An Alltrax AXE4834 300 AMP controller. A MARS ME0709 18 HP / 300 AMP peak motor (8 HP / 125 AMP continuous).

**My current (no pun intended) top speed is 45 MPH.**

To go faster I plan on adding 2 more batteries which will give me a 72 volt system. Of course I will have to upgrade my controller to either the AXE7234 200 AMP or the AXE7245 450 AMP.

To increase the range I need to up the AH, and that's where I am confused. I know in the parallel configuration the Amp Hours are added up, but where do the extra Amp Hours go when I add the additional two batteries like I am planning to do? I realize I will be carrying the additional weight.

**If I limit myself to 45 MPH top speed Is my range going to increase at all?**

In a series circuit, amps is constant on each battery, and voltage increases with each cell. In parallel circuits, voltage stays the same, and amps are added per battery....

4 12v 20ah batteries in series = 48v 20ah pack

4 12v 20ah batteries in parallel = 12v 80ah pack (in theory)

I'll be interested in the replies as well. My understanding - more like an educated guess - is that the extra amps go to increase power, and with more power you can run more efficient motors, which, along with good controllers, increase the range by drawing less deeply from each battery than would a system with fewer batteries. I have a ZEV with a 72 volt system, but the batteries are only, IIRC, 40AH each. To increase range within a given voltage you need to increase the AH rating of *all* the batteries, equally. So if I could squeeze 6 50AH batteries into the same same space as the 40AH batteries, I'd get more range. You could get more range from your existing system by staying with 48 volts but replacing the batteries with, say, 70 or 100AH units. If you like the bike's power and speed with the setup you have, I'd first look at higher capacity batteries...

You have to look at the total energy available:

In the 4x12V 55Ah setup, you have 48Vx55Ah=2640Wh of energy

In the 6x12V 55Ah setup, you have 72Vx55Ah=3960Wh.

If you run the scooter at the same speed at both setups it will draw about the same amount of energy, meaning you will get longer range with the 72V pack.

With the higher voltage you can go faster which of course takes more energy.

Additional weight of the extra batteries will consume a little extra as well.

JohnnyJ has it right. But there's one extra advantage of a higher voltage system. Because power is volts multiplied by amps if you increase the volts you proportionally decrease the amps required for the same amount of power. In turn lower amps mean less heat generated. Less heat generated means less resistive losses (resistance goes up with heat, and I believe that heat goes up as a function of amps-squared). "Less losses" is another way of saying "more efficient". Also, lower amperage means one can use smaller cabling.

If you look at all the major 4-wheel EVs you will see high system voltages. The VX-1 uses a higher voltage than most 2 wheel EVs out there and uses a high RPM motor with a reduction gear to bring it down to usable range (and also increase the torque).

Hope this helps.

John H.Founder of Current Motor Company - opinions on this site belong to me; not to my employerRemember:" 'lectric for local. diesel for distance" - JTH, Amp Bros||"No Gas.EXCELLENT Explanation, just what I was looking for. Basically Amp Hours are half the story and it's Watt Hours that tell the full story. So if 2,640Wh takes me 10 miles (rounded down for easy math) that's 264Wh per mile, than 3,960 divided by 264 will take me 15 miles. That is goodness.

Thank you everyone else for your comments as well, I am learning here, and you are helping tremendously.

When comparing wh/mile, be aware that a 4x12V 55Ah battery only has a usable capacity of ~1300Wh due to a combination of peukets effect, voltage sag, and the use 80% rule.

This derating varies with battery and chemistry (for instance a 48v 55Ah LiFePO4 battery has a usable capacity of 2100Wh)

Matt

Daily Ride:

2007 Vectrix, modified with 42 x Thundersky 60Ah

Vectrix 60Ah Lithium Tyres Fuel Registration Insurance cycle analyst 2 x TC Charger & MC

conversion

Hi Matt, good stuff, thank you. Please don't feel like I am questioning you, I agree that LiFePO4 are more better, lol, however wouldn't the 80% rule yield 2,112 Amp Hours of the lead acid battery pack. Where as 1,300Wh is closer to 50%. Now I have heard that for lead acid you pretty much expect 50% of the Amp Hour rating, which would be in line with what you are saying.

Either way I love hearing that the LiFePO4 are that much better, they are still three times more expensive but you are getting roughly 60% more umph, that would take my 10 mile range and make it 16 miles, and I am all for that

Take a 48v 55Ah lead acid battery.

If discharging at 40A continuous, only 35Ah will actually be recoverable at that discharge rate.

The other 15Ah is only usable at a much lower discharge rate.

At 40A continuous, you won't actually get the full 48v, but it will be pretty close to on average.

To avoid going completely depleted, it is advisable to only aim to use 80%, mainly to avoid reversing the weakest cell (so when discharging to ~42v or whatever your cut off is, no cell is below 0v)

Reversal happens when the discharge current put through a cell is greater than what it can supply.

It does not have to be completely flat for this to happen

It won't be as much of a problem when the battery is new, however, when it ages a bit, the capacity loss is not uniform.

The same 80% rule applies to LiFePO4, its just theres no peukets to worry about.

Matt

Daily Ride:

2007 Vectrix, modified with 42 x Thundersky 60Ah

Vectrix 60Ah Lithium Tyres Fuel Registration Insurance cycle analyst 2 x TC Charger & MC

conversion

Excellent discussion. Other point to add is that more batteries == more weight == more energy required to move the bike.

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