How to Use a Watt Meter

[Ltc433]

Hi all,

So I have wired up my watt meter. Firstly I have done it incorrectly as I should have just run:

Battery > Thick Black wire 14 gauge > Watt Meter > Controller
Battery > Thin Red wire 24 gauge > Watt Meter > Insulate the end of it.
Battery > Thick Red wire 14 gauge > Controller

So I will cut it and resolder. However how to you actually use it? On a recent trip I came back and measured the voltage drop. 54.1V to 50.8 Volts at 8.4 miles. It's an eleven amp hour battery. I thought it would tell me how many amp hours I have left. How can I calculate it?

 

[dustNbone]

You'll have to provide more info on the particular meter you're using, there are several types that connect and operate differently.

 

[john61ct]

Find the manual, read it, then post a link to it here, along with any remaining questions

 

[aroundqube]

And that's how the What Meter got its name.

 

[motomech]

On a recent trip I came back and measured the voltage drop. 54.1V to 50.8 Volts at 8.4 miles. It's an eleven amp hour battery. I thought it would tell me how many amp hours I have left. How can I calculate it?

You have "range anxiety".
I've found it much easier to mount a Voltmeter that can be seen riding. I use a Low draw LCD one because the LED's, unless they can be turned off, will run the pack down. W/ just two liteweight leads across the power wires, it's simple compared to installing a shunt or cutting into power wires.
To over simplify, ebikes in the 1000 Watt range (low 20's MPH) get around 1 1/2 miles per Ah batt. capacity. Pedal hard and it gets closer to 2 Miles/Ah or go 30 MPH and you are looking at 1. In the middle it doesn't vary much.
At the very least, when the Voltmeter is halfway down, it's time to turn around and head for home.
Unless you are always pushing for new horizons, pretty soon you will know how much battery you need for all your common routes.
If you can't stop thinking about how much juice is left, you need more batteries

 

[E-HP]

On a recent trip I came back and measured the voltage drop. 54.1V to 50.8 Volts at 8.4 miles. It's an eleven amp hour battery. I thought it would tell me how many amp hours I have left. How can I calculate it?

You need a watt-hour meter, not a watt meter, since you're trying to measure energy. It's possible that your meter has that functionality.

 

[Ltc433]

On a recent trip I came back and measured the voltage drop. 54.1V to 50.8 Volts at 8.4 miles. It's an eleven amp hour battery. I thought it would tell me how many amp hours I have left. How can I calculate it?

You have "range anxiety".
I've found it much easier to mount a Voltmeter that can be seen riding. I use a Low draw LCD one because the LED's, unless they can be turned off, will run the pack down. W/ just two liteweight leads across the power wires, it's simple compared to installing a shunt or cutting into power wires.
To over simplify, ebikes in the 1000 Watt range (low 20's MPH) get around 1 1/2 miles per Ah batt. capacity. Pedal hard and it gets closer to 2 Miles/Ah or go 30 MPH and you are looking at 1. In the middle it doesn't vary much.
At the very least, when the Voltmeter is halfway down, it's time to turn around and head for home.
Unless you are always pushing for new horizons, pretty soon you will know how much battery you need for all your common routes.
If you can't stop thinking about how much juice is left, you need more batteries

I bought a Turnigy meter. I read the manual, however no-one actually explains how to use it. ie how it actually is used to calculate performance of the battery and measuring how much distance/battery you have left.

My original thoughts were the Turnigy Watt Meter would tell me how many amp hours i had left. It does not. It tells you how many amp hours you have used (I think)? It also tells you peak volts/amps/ used? It tells you how many watts are currently being used.

Real-time Amps 0.00A
Real-time Volts 54.1V
Peak Amp Hours 0.000Ah
Peak Watts 0.0Wh
Peak Amps 0.00Ap
Peak Voltage Drop 00.00Vm

Haha. I don't have range anxiety. I literally have no idea how far my bike goes. Simple as that. I also would like to travel further but the longest journey has only been about 15 miles. I'm also just interested in how the battery works etc and what the numbers on the watt metere mean. My LCD has a volt meter built in.

"W/ just two liteweight leads across the power wires, it's simple compared to installing a shunt or cutting into power wires."

So Volt Meter vs Watt Meter. Why do people use the Watt Meter?

Here is the manual for the LCD

http://www.szktdz.com/en/news_show.php?article_id=568

 

[john61ct]

1. Fill battery up, set Ah counter to zero
2. Ride until your pack is at 3Vpc then stop. Note you should in normal usage try to stop & recharge long before that point for longevity, this was just a capacity benchmark.

Say for easy math your pack capacity is 10.0Ah

Note that will drop as it ages, 9.5Ah is 95% SoH

3. Fill battery up, reset Ah counter to 0. Go out riding as normal. After 4Ah you are at about 60% SoC, aka 40% DoD. Means if you can ride some more, use up another 4Ah and then stop, and you won't be wearing the pack out too much.

Stopping and recharging at 50% the pack will last **lots** longer, but you're carrying extra weight.

Drawing down past 90% every time will murder the pack, really lose tons of cycles.

Depending on speed, winds, hills, load etc you'll start to get a feel for miles per Ah, how much actual range you have left, when you need to start heading back home.

Or if commuting, how big your pack needs to be.

 

[dilkes]

In simple terms:
The wattmeter can measure Ah used and Wh used. It has no way of knowing how much was in the tank when you started. You need to supply (or guess at) that and do the math.

The post above gives some ideas on determining the starting battery capacity.

 

[john61ct]

There are "battery monitors" that try to accurately calculate SoC%.

The owner enters in the actual Ah capacity, needs to keep that updated as it changes.

Also CEF and Peukert need to be adjustable.

And ideally the 0% voltage can be user-defined, and both manual and automatic 100% resets are enabled, the latter needing both CV voltage and endAmps specified.

Usually a 4-8% accurate guesstimate is as good as they get, even those costing hundreds of dollars.

And that good requires frequent 100% resets.