5v voltage drop typical?

[Dorkyman]

I have two XPst bikes, one with the 500Wh battery and the other with a new 670 Wh battery. Just noticed that under full power (18 amps) the voltage drop from both batteries is about 5v. In other words, if resting voltage is 48v, then full power drops that to 43v. Is this typical? Seems like a lot to me.

 

[6zfshdb]

This may or may not be normal. A lot depends on where the voltage is being measured. Most bike makers try to save money by using wire that is the bare minimum gauge. This can cause a voltage drop and will vary for different bikes. A 5 volt drop measured at the motor might be normal whereas a drop of 5V at the battery could indicate a problem.

I get a 3 - 4V drop with an 18 amp draw on my bike, but it's a different make. Perhaps someone with the same bike can offer a more relevant opinion.

 

[il Munduato]

I concur with the above...
I'll also add that inexpensive batteries typically don't have a high continuous output rating that can also result in V drop.
Then add that your batteries (if 48v) are on the small side having fewer cells in parallel which also diminishes it's ability to output a high continuous current.
Lastly 18a is a lot to put out continously in general and these bikes are by design to assist pedaling.. not be riden as an electric motor bike.
So probably best to use your gears and pedal to keep things <10a for the most part if you want to get any longevity from your battery.

 

[harryS]

Seems about right for an XP battery, to drop about 5 volts under full throttle, 500WH and 670WH is 48V10AH and 48V14AH respectively. THe latter is about as much as they can stuff into an in-frame battery, If it's like most ebikes, the XP measures the voltage at the display, but the controller runs its own check, Both are essentially across the battery.

It's a design decision. For most people, a 10AH XP battery gives satisfactory performance, It don't matter if it sags as long as it doesn't shut off onfull throttle when the bike is running along at 40-50%, Then customers would complain,

 

[Dorkyman]

I contacted Lectric customer support, and they referred me to a technical person at the company. He emailed to me a test format. Basically, fully charge the battery, note the voltage, then ride one level mile out and then back on PAS 2 without throttle application and free-wheeling the pedals. Then note the voltage, rider weight, tire pressure, battery serial number, and bike serial number. Photos for verification.

Lithium batteries have a finite life. What got me curious is that the smaller battery is now about 3 years old, but the larger battery was just purchased at the $350 Black Friday price. And I'm still curious why a battery supposedly certified to UL2271 doesn't have a UL sticker. But maybe they don't require a sticker in the first place. I'm just thinking it's only a question of time before some apartment or condo management company bans ebikes that aren't certified--and how would the rider prove they were? Because the manufacturer says so in their advertising? Is that good enough?

I'll do this battery test the next warm-ish day here in Oregon. May be a while...

 

[Slaphappygamer]

I get a 3 - 4V drop with an 18 amp draw on my bike, but it's a different make. Perhaps someone with the same bike can offer a more relevant opinion.

Same case for me. My battery is 13s 4p with Samsung 35E cells.

I’ve been using my controller at 25A max and have never seen more than 4 volts drop.

 

[m@Robertson]

What you are describing is commonly called 'voltage sag'. It happens to any pack when you put it under load. The stronger the load and/or the smaller the battery, the worse the voltage sag. So, I have great big 35ah battery packs and they only sag by a volt or two under a 45-60a (!) load. A 12ah pack under a 30a load (a standard BBSHD and a typical mtb-sized battery pack) is going to sag 2-3v. ish.

I suppose sag will also maybe be affected by the cells in use, too.

Anyway, this is another reason to buy bigger batteries.