should wattmeter and dmm reading be the same?

[footpump]

hi all I have a enerpack softpak battery which I am going to try on my 350w ,
I have made up a lead as follows enerpack has xt90 , so I have xt90 to xt60, with a wattmeter in between , which will then connect to controller.

if I measure my bottle battery with a voltmeter I get a reading of 40.8v
if I connect the source side of wattmeter to the +/- I get reading of 41.91 in top right hand side of wattmeter

if I measure my enerpack at its xt90 connecter with voltmeter it shows 41.6v if I connect lead to battery /with wattmeter also connected the wattmeter is not lit, but the lead reads 41.6v so lead would seem to be ok?

 

[Deleted member 4366]

Why don't you try the wattmeter on both batteries to see if you get a consistent error?

 

[footpump]

wattmeter on enerpack reads 42.71 so it would seem wattmeter is reading 1.1 v higher on both batteries than dvm.
one reason I want to try the wattmeter is that when the lcd3 display drops to one bar out of 4 for battery capacity,
I have no real idea how much is actually left, and get worried and head for home as the last mile from home is hilly.

 

[Nealh]

LCD3 has a voltmeter reading which I find is accurate and matches my DVM. In use a quick press of the on/off button cycles through the menu showing distance, odo & voltage.

 

[harrys]

In my experience, and I had three wattmeters, none of them read the same voltage when I strung them in series.

They did read the same AH within +/- .1 AH.

 

[wheeliepete]

I've found those watt meters are a bit out on voltage compared to my DVM too.

 

[Deleted member 4366]

You will learn the pattern of your battery's behaviour from the wattmeter. That's more important than any absolute readings.

They're never 100% accurate, but you'll know exactly when your battery will cut off because it will always be the same voltage on the wattmeter and you'll be able to predict when that will be from the Ah used. The Ah on the wattmeter will be repeatable, so your 13Ah battery might cut off when 10Ah or 15Ah is shown, though whatever shows should be the same each time for the same sort of journeys.

Battery capacity varies depending on how much current you take from it, so it's probable that the capacity will be less for a hilly ride than a flat one.

 

[Kinninvie]

Dont wory about the voltage,just concentrate on the Ah readout as that will give you the info you need to get home without the walk of shame!!

 

[footpump]

thanks all for info, as yet not fitted wattmeter.
full charge lcd3 shows 41.8 24.9 miles covered lcd3 shows 36.5v
2 bars showing but this will soon drop to 1
(27 miles other day down to 1 bar bike felt a bit lethargic)

battery specs say cut off 28v so if display at 30v I'm near empty.???

will fit wattmeter tomorrow

 

[wheeliepete]

Your controller should cut off at around 31v unless you have changed it. Fit the watt meter and you can see your Ah used. Power will drop off as battery voltage reduces.

 

[minexplorer]

hi all I have a enerpack softpak battery which I am going to try on my 350w ,
I have made up a lead as follows enerpack has xt90 , so I have xt90 to xt60, with a wattmeter in between , which will then connect to controller.

if I measure my bottle battery with a voltmeter I get a reading of 40.8v
if I connect the source side of wattmeter to the +/- I get reading of 41.91 in top right hand side of wattmeter

if I measure my enerpack at its xt90 connecter with voltmeter it shows 41.6v if I connect lead to battery /with wattmeter also connected the wattmeter is not lit, but the lead reads 41.6v so lead would seem to be ok]

I have same meter .It reads a half volt more than my multi meter as well.Have it permanently on handlebars as a display,wish it was brighter can hardly see in daylight.Let me know if u find that annoying too an find a way to brighten it up.I have found it very rainproof with a little silicone added in the wire entry points.Other watt meters seem to be backless panel mount types.i screwed a light mount to the bottom. An used d8vehs method , replaced thick red wires with a small 18g wire from battery to input side.

 

[Deleted member 4366]

IIRC, you can hack the brightness by changing a resistor inside.

 

[minexplorer]

IIRC, you can hack the brightness by changing a resistor inside.

Thanks d8veh . No clue what one and what rating it needs to be tho.

 

[Deleted member 4366]

Something about it here
https://endless-sphere.com/forums/viewtopic.php?f=3&t=13607&start=285

I don't have my GT wattmeter open to look at, but all the others are more or less the same. you can see two pads on the end of the LCD board for the backlight LED. Nearby, is a resistor around 120 ohms with a vacant parallel pair of pads next to it. You could try touching a 1k resistor to those two pads, which should make it go brighter. I don't know how low you can go before the LED pops, but i would have thought 500k would be enough.

This guy changed the blue LED for a white one

 

[footpump]

fitted wattmeter but a tempory fitting about 4" above bottom bracket and affixed by cable tie.
lots of pas 4 today , lcd3 showed 4 bars then dropped to 2 bars down to one bar at 36v on lcd3 screen.
25 miles covered , I found trying to see the wattmeter readout in sunlight near nigh impossible, ok in the shade. but had to be on my knees to read it ,even with bifocals.

whatmeter reading at rest after journey showed 36v vs 35v on lcd 3
the ah reading fluctuated between 0,07 ah and 11, forgot to see ah reading prior to setting out on full charge.

 

[wheeliepete]

Those figures on the bottom left of screen cycle through peak amps AP, peak watts WP, consumed amps Ah, consumed watts W and Minimum voltage VM. So you have used 11Ah of your battery. It will only show voltage at start of journey because you havn't used any power.

 

[Deleted member 4366]

Ah will always be zero when you set off unless you use a separate power supply to power the meter. The Ah reading is the Ah used since you switched it on. it doesn't have a clue how many you already used or what's in your battery.

 

[minexplorer]

Something about it here
https://endless-sphere.com/forums/viewtopic.php?f=3&t=13607&start=285

I don't have my GT wattmeter open to look at, but all the others are more or less the same. you can see two pads on the end of the LCD board for the backlight LED. Nearby, is a resistor around 120 ohms with a vacant parallel pair of pads next to it. You could try touching a 1k resistor to those two pads, which should make it go brighter. I don't know how low you can go before the LED pops, but i would have thought 500k would be enough.

This guy changed the blue LED for a white one

Thanks d8veh will have a look inside .The resistor method sounds better

 

[footpump]

hi all prior to fitting a wattmeter I assumed it told you what the wattage/amp hour was. in the battery.
so my fully charged 17ah battery I was expecting to see a 17ah reading on wattmeter which would decrease as capacity was used up.

went out the other day ,stopped 3 times battery was turned of ,so ah there would be 3 separate ah readings on wattmeter? which I believe I should add up for ah used?

today first ride out with my enerprof softpack 36v 13.8ah there is no on/off switch on softpack , so did 19.5 miles ah reading on wattmeter 6.79
and battery level has just dropped to 2 bars dvm meter reading is 37v

mainly pas 3 , but 4 used about 4 miles, pas 5 for a short hill.

 

[Deleted member 4366]

That's 12.5 wh/mile, which sounds about right.