Stupid battery questions

[CynicalZombie]

I have about 1500 miles on my RadRover 5’s stock controller and about 150 on the Bolton Upgrade.
Now that I have the ability to see the battery’s voltage I have questions...

Disclaimer: I don’t understand batteries

When I’d ride with the stock controller and I’d use a bunch of power I could see a battery bar disappear... then when I was back to normal PAS 2, the bar could come back.
Now that I can see the voltage I’m trying to understand what it all means. My stock 48V battery shows up around 54V when fully charged. I’ve read that that is normal. I know that the cutoff on the Bolton controller is set to 40V. On my last long ride I hit that 40V, lost power, then it recovered to like 43V and I was able to make my way back on PAS 1. So does that mean I have 14 usable volts?

What happens with a 52V battery? Where is the cutoff? What is the setting on the upgraded controller for a 52V battery?

 

[Sierratim]

The 'useable voltage' for a battery pack is determined by both the Battery Management System (BMS) and the bike's specific controller. The BMS is usually built into the battery pack. Its job is to prevent damage to the pack or any individual battery cell in the pack by either over charging or over discharging any cell in the pack. So, yes, in your case you have a 14V spread between the min & max voltage available from the pack.

Energy, not voltage, is what ultimately makes tour bike go. The chart posted by @Timpo lets you estimate the available enerygy from the battery pack. At a max voltage of 54V and a min of 40V you're basically going from 95% to 5% battery capacity, meaning you can use up to 90% of your battery capacity. For your 672Wh rated battery, you'll be able to use ~605Wh. Why not 672Wh? It would shorten the battery's service life substantially. For maximum service life it's actually recommended to not go below ~20% charge and not exceed ~80%. This would yield 403Wh for max service life.

You can think of electrical voltage like water pressure in a hose, the higher the voltage the more flow. Flow of what? Electrons, which equate to energy. So a higher voltage battery can push more energy into any given motor boosting motor power. For a 750W motor, going from 48V to 52V can provide an additional 15% or so in power. Because all motors operate at less than 100% efficency, some of this will be lost as additional motor heat. Can your motor handle this? Can't say from the published specs. Other brands, like Juiced, promote a 52V upgrade so their motors are apparently OK with this.

Assuming the same % cutoffs as a 48V battery, you'd get 58V-43V for for the same useable 90% of capacity with a 52V battery. Will this add range? Depends on the battery's energy storage capacity, usually expressed in Watt-hours (Wh). Since Juiced publishes specs on 48V vs 52V batteries I'll use their figures for this example. Juiced rates their batteries in Ah (Amp-hours). Multiply by the rated voltage to get Wh. So, the 'Standard' 48V 8.8Ah battery has an energy capacity of 422Wh. Their 'Super Extended' battery is rated at 52V 13Ah = 676Wh, a 60% increase.

So a 52V battery will increase your motor power, if the motor can handle the higher operating temps. The available 52V battery packs for Juiced bikes offer at least 60% more battery power. More motor power, higher motor temps, more range, and of course more $. That's a set of trade off you'll need to consider...

Hope this helps.

Juiced Bikes 48V vs 52V article

Battery University has a number of excellent articles on lithium batteries.

 

[legsofbeer]

Now that I can see the voltage I’m trying to understand what it all means. My stock 48V battery shows up around 54V when fully charged. I’ve read that that is normal. I know that the cutoff on the Bolton controller is set to 40V. On my last long ride I hit that 40V, lost power, then it recovered to like 43V and I was able to make my way back on PAS 1.

That's consistent with what I've seen on my radrover 4 with the bolton upgrade. Assuming you're using the instantaneous voltage display setting instead of the one that tries to be "smart", you're going to see significant variance from minute to minute in the apparent voltage. This is because the battery's output voltage drops the higher it is loaded. Take your fully charged 54.0 v battery and charge up a hill on max throttle. The voltage displayed might drop into the 49s before you get to the top. Now stop riding, and watch the voltage tick back upwards to maybe 52.something. You've just knocked off about 1.5 volts of your battery's capacity. This really should be expressed as an WattHour value, but we'll take what we can get.

On the riding to shutoff with the bolton controller cutoff set to 40.0 v, know that there are two shutoffs. The first is from the bolton controller, and if you start seeing instantaneous voltage values below 40 volts, it will shut you off within a few minutes. But... as you saw, if you let the battery rest a few minutes the instantaneous voltage will rise above the shutoff value, then you can power cycle the controller and nurse the bike to get back home.

The second shutoff is from your battery's Battery Management System (BMS). This voltage cutoff threshold is a lower value than the bolton controller's, and has nothing to do with the controller. When the BMS cuts you off you are done until you recharge the bike. This is the hard limit to protect the battery (and reduce warranty crapola from people abusing their battery).

 

[CynicalZombie]

A BIG thank you to everyone above!! Very useful info and a good video!

As Sierratim noted above I’d have about 605Wh that are usable. Let’s just say 600 even for math’s sake.
Does a watt hour mean I could use 600 watts of power for 1 hour?
Would that also mean I could use 100 watts of power for 6 hours?
Just trying to understand! Thanks again!

 

[legsofbeer]

Does a watt hour mean I could use 600 watts of power for 1 hour?
Would that also mean I could use 100 watts of power for 6 hours?

For overall range, yes, it mostly works like that. But you can also draw higher numbers, for instance the stock controller will let you draw near 750w.

Yes, but in my general impression (2900 miles) high wattage draws kill the battery more than the the same net power draw at lower wattages. For instance, using the stock radrover controller, 750w for 10 minutes kills the battery more than 375w for 20 minutes.

 

[Sierratim]

A BIG thank you to everyone above!! Very useful info and a good video!

As Sierratim noted above I’d have about 605Wh that are usable. Let’s just say 600 even for math’s sake.
Does a watt hour mean I could use 600 watts of power for 1 hour?
Would that also mean I could use 100 watts of power for 6 hours?
Just trying to understand! Thanks again!

On a straight forward math basis, you are correct, 600Wh = 600W x 1hr = 100Wh x 6hr, etc. But as @legsofbeer points out, chemicaly based batteries don't discharge linearly. And as you've noticed, batteries can even apparently recover energy after resting a bit. This all has to do internal temps and temporary oxidation on the electrodes due to short term high currents.

Bottom line, you'll get the best mileage per charge by riding conservatively, just like you'll get the longest service life by charging conservatively.