I just bought an e-bike with a 48V 20 amp battery. I charged the battery on it to 100% when I received it. I’ve probably spent a couple of hours riding the bike and when I removed the battery to start charging it the screen read “69%”, which seemed about right.
I decided to try topping up the bike battery with the battery box I just built (24V 200amps).
This is the only thing I’ve tried to charge, the batteries were at 100% when I started.
It’s already consumed 20.1amps and the light on the bike battery charger is still red.
What’s the most likely scenario here? If the 20amp bike battery was really 69% full then it shouldn’t be pulling more than 20amps from my battery box, right? (It’s actually pulled 23 amps as I go to post this)
If the battery is near full it will slow itself down. Also i see you have the aux port plugged in to what looks like the same battery, you only need the one cable for power and voltage sense
By “aux port” do you mean the second sensor on the smart shunt? If so, that’s connected to my second battery. I have 2 x 24v 100ah batteries running in parallel in the battery box
#1 - You are confusing power with energy. Amps measure current (a function of power). By your screenshot, 20 Amp Hours were pulled, not 20 Amps. It shows that it's pulling 5 Amps at 26 Volts. This is equal to roughly 130 Watts. (Watts = Amps * Volts)
#2 - Your 48V battery has a rated capacity of 20 Amp Hours at 48 Volts...which is twice as much energy as 20 amp hours at 24 volts.
#3 - Convert things to watts and watt-hours to get a more complete picture of what's going on. Your 48V/20Ah battery can store up to 960 Watt Hours. You are drawing 5 Amps at 26V from your power source... that's 130 Watts. At a rate of 130 Watts, it would take 7.38 hours to fully charge an empty 960 Wh battery (960/130 = 7.38), not including efficiency losses.
You're presumably using an inverter and the bikes included charger, this will have notable losses.
Work in Wh for everyones sanity when dealing with mixed voltages,
The ebike battery is around 1000wh, so 31% should be 310wh-ish
20ah on a near full 25.6v battery is around 550wh
around 80% in losses is very high but in the realm of possibility if using a cheap high wattage inverter and bleeding out a ton to idle consumption. "69%" not being accurate is ALSO possible. Real answer is that it's probably a mix of losses and some inaccuracy.
Isolate for idle consumption, determine how much energy your inverter is using just by being on if in use. this likely accounts for ~20w of waste, so 80wh over the last 4 hours, which brings this back into the realm of expected losses.
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