Inexpensive voltage monitoring

[dogman dan]

Thanks to Sam Texas for the thread that pointed these out to me. Can't seem to find that thread now though.

EDIT. Can't read the display if it's in the sun. Stop reading if you need it for outside.

Many are on a budget, don't have money for a Cyclanalyst, or even a turnigy wattmeter, and would like to at least monitor the voltage of their battery. Often the solution has been a cheap voltmeter from harbor freight or something.

Here is another great solution. 15-120v capable LED display voltmeter. 8 bucks shipped from china from various Ebay vendors. I ordered two, and they came in about 3 weeks free shipping.

It's about the size of your thumb, so big enough to read, but not hard to mount on handlebars or battery box. Has the clips to pop into a panel if you have one. No telling if it's waterproof, but you could mount it underneath something clear, even just inside a scrap of sandwich bag. This one is nice because it runs on any voltage from 15-120v. Others I've seen on ebay needed a seperate lower voltage input, and had more limited voltage ranges.

It's NOT particularly accurate. I got two, and they read .1v different from each other. Adequate though, for telling if your battery is charged when you set off on a trip. You see 50v on the display when you think you just charged to 56v, you know something is not right.



Another pic, showing how I set mine up. I use andersons, so I made an adapter that goes between the battery and the controller with a wire to the voltmeter.

I can then move the thing around from bike to bike, to mower, to weedwhacker, whatever. Now I can have some simple volt monitoring on any of my bikes, without uninstalling one of my two CA's.

 

[dogman dan]

Ouch! Wrote too soon. I just went out and mowed the lawn, and this voltmeter is completely unreadable in the sunlight. You can barely read it if you shade the display.

Oh well, I was thinking they were so cool. Still could be a decent device to carry to check voltage at the start of the ride, but it will be a real pain to use this for monitoring as you ride. Have to stop to safely have a peek at it. At least it's small.

It's readable enough when located in the shade inside one of my pannier bags on the commuter bike. Or if you shade it with your hand and squint hard enough at it. Definitely only usable at night, or while not moving.

Better than nada if you can't afford a CA. We'll see how long it lasts.

 

[deVries]

Ouch! Wrote too soon. I just went out and mowed the lawn, and this voltmeter is completely unreadable in the sunlight. You can barely read it if you shade the display.

Oh well, I was thinking they were so cool. Still could be a decent device to carry to check voltage at the start of the ride, but it will be a real pain to use this for monitoring as you ride. Have to stop to safely have a peek at it. At least it's small.

It's readable enough when located in the shade inside one of my pannier bags on the commuter bike. Or if you shade it with your hand and squint hard enough at it. Definitely only usable at night, or while not moving.

Better than nada if you can't afford a CA. We'll see how long it lasts.

It's still a great idea. You just need to find a bigger display with bold numbers & backlit maybe too. Bigger is better.

Ebay searchers begin... your search engines! :lol:

 

[dogman dan]

LCD display would work, but I haven't seen that yet. My first simple idea didn't work, putting a sunglasses lens over the display.

I don't regret blowing 16 bucks on a couple of them. They just aren't good for reading voltage as you ride. Oh well.

 

[999zip999]

Like a wet dream always best befoe the lights come on.

 

[wesnewell]

When I want to see the voltage in direct sunlight I just shade it with my hand and don't have a problem reading mine. I using a green one installed but also got a blue one which I haven't tried yet. BTW, you can get lcd voltmeter displays on ebay also that will run on pack voltage up to 60V. If you want higher than that you can to request it up to 500V iirc. Under $20.

 

[deVries]

When I want to see the voltage in direct sunlight I just shade it with my hand and don't have a problem reading mine. I using a green one installed but also got a blue one which I haven't tried yet. BTW, you can get lcd voltmeter displays on ebay also that will run on pack voltage up to 60V. If you want higher than that you can to request it up to 500V iirc. Under $20.

Have you found any with much bigger displays than thumb size???

Thanks.

 

[staft]

I just bought one of these 2 days ago after dogman and wesnewell pointed it out as an option for me in another post (thanks as always!). I have a dslr camera screen that has the same problem - I used the cut-off top of a square tums bottle, taped black, and with an old slide viewer eyepiece (single lens) installed in the cap. There is a clip on screen protector on the "open" end to allow me to quickly mount it to the camera lcd. Works wonderfully, and magnifies my view of the lcd the perfect amount. I will most likely try something like this on my bike when meter arrives, and see if the black shade will allow me to look down into the dark well while moving. Magnification might help, but might not be needed.

BTW, when looking around I found slightly more expensive meters that have a shunt and monitor volts and current. Could this be used on an ebike?
http://www.amazon.com/Volt-Meter-Digital-Shunt-200V/dp/B005HBBZEM/ref=sr_1_9?ie=UTF8&qid=1339277497&sr=8-9&keywords=volt+meter

 

[staft]

And how do I post inline images here instead of link? Can't find that info in FAQ.

 

[HAROX]

.

 

[staft]

My camera solution would make the meter waterproof at the same time, I think.

 

[dogman dan]

It's not really a problem of too small, Maybe red was just the wrong color . In the sun, it just blends into the color of the unlit led. So it looks like the unpowered led in the pic, all zeros.

You can shade it with your hand and see it, but for me being half blind and old doesn't help much. I wouldn't recomend trying to shade it with one hand, then squint at it while going 30 mph down the road. If you stop, you can see it. I suppose you could mount it in the bottom of a toilet paper tube.

 

[SamTexas]

Thanks for the report dogman. Mine should arrive any day now.

If you stop, you can see it.

Great. I don't have a plan to have it on all the time. I plan to install a switch so I can look at the voltage when I need to. May be it'll work out for me.

 

[staft]

I suppose you could mount it in the bottom of a toilet paper tube.

I don't think the shade needs to be that deep. My tums bottle viewer is less than 2" off the lcd, and is perfectly viewable in brightest daylight. Unless the sun is shining straight down, it shouldn't be a problem. If you capped the well with one of those fresnel magnifiers posted above it would keep the weather out, too.

 

[wesnewell]

Great. I don't have a plan to have it on all the time. I plan to install a switch so I can look at the voltage when I need to. May be it'll work out for me.

I have mine wired to controller leads and it's on whenever there's power to the controller. It only uses 20ma max iirc, so it's not enough to worry about.

 

[amberwolf]

If you don't mind the LEDs having notably shorter lifespan, you could open them up and change the current-limiting resistors in there, if it uses them, on the segments or the common anode or cathode of each digit. Probably is setup for 5-10mA on each segment right now, and you could possibly double that for what would likely be significantly more brightness.

If changing resistors is not an optin, then if the drivers for the LEDs are not part of some custom chip, you could also find their pinout on the web, and see about increasing the voltage they use, if their specs permit it. That would also probably change the current flow thru the LEDs, and brighten the display (again, at the sacrifice of lifespan).


Regarding magnification--remember that when you make something larger with a Fresnel lens, it's making the light from it dimmer overall, as some of it is lost to reflection from the other side of the lens, some to internal refraction/reflection/absorption, and the magnified image is larger thus the same light is spread over a larger area, making any one same-size point on it dimmer than it had been before.

Regarding shading--if you use something like sunglass lenses or window-tinting or old display lenses off a VCR or clock, use the same color as the LEDs themselves. This will help pass only the light from the LEDs thru, and not as much of any other ambient light, increasing contrast.

Carefully painting the background around the LED segments with flat black paint will also help, as usually they are a gray of some shade.

Removing any "clear" cover over the LEDs will also help, as it lets just that little bit more light thru.

 

[SamTexas]

Great. I don't have a plan to have it on all the time. I plan to install a switch so I can look at the voltage when I need to. May be it'll work out for me.

I have mine wired to controller leads and it's on whenever there's power to the controller. It only uses 20ma max iirc, so it's not enough to worry about.

Good to know. Thanks wesnewell. Is that around 1W?

 

[dogman dan]

Must be less. I plug my 48v ping into the 20 amp controller, and I see 3w. I just plugged in the CA by itself, and it must use something, but it shows as 0 watts. Then plugged in the little voltmeter, and still shows 0 w.

So it would take a few hours to drain my ping. 700 hours if it was one watt of 48v, and it seems to be less.

BTW, I looked at hundreds of ebay ads yesterday looking for a similar meter with LCD display that would be readable in the sun. Only thing I found was like other meters I didn't like. More expensive, and requiring a second input of less than 15 v to power it up. Sure, maybe you could run it on your throttle or halls voltage, but it seemed like a real PITA to me compared to these two wire meters with a huge operating range.

 

[wesnewell]

Typical usage is 5-15ma, 20ma max. 5ma @48v=.24W if my math is correct. Less than 1W at 20ma.

 

[Gregor]

I have a few of these also and a little "shadow box" like a paper towel tube cut down to 3 inches or so helps a lot. Cheap enough to keep on your handlebars without worrying about it being stolen. My search of ebay showed many voltage ranges available--mine is 30 to 70 volts, but is not too acurate below 40 volts--a poor man's warning of when your running your lipos or lifepo4's too low.

 

[parajared]

Why not just run a $5 cell checker to one of your balance leads?
It certainly would not give you a good picture of how the whole system is doing, but assuming your batteries discharge at about the same rate monitoring just one battery should be fine.

Here's a tiny $5 one with an alarm and flashing light but only displays one cell at a time.
http://www.hobbyking.com/hobbyking/store/__19945__H_King_Cellmeter_6_Lipo_Life_Li_ion_Cell_Checker_Alarm.html

or this $15 one that displays all eight cells
http://www.hobbyking.com/hobbyking/store/__10952__Cell_Log_8M_Cell_Voltage_Monitor_2_8S_Lipo.html

this $10 one, displays how much battery life is left in %
http://www.hobbyking.com/hobbyking/store/__19946__H_King_Cellmeter_7_Lipo_Life_Li_ion_Nimh_Nicd_Digital_Battery_Checker.html

 

[The Mighty Volt]

One thing I always wanted was a Large-Screen display which allowed me to watch my strings sag under load, sort of like a Cell-Log, but with 24 channels and far less current draw.

 

[999zip999]

Me to Volt but we all need a cell monitor for 12s-24s ect thru are eyeshades. We all know a problem child ( cell) and just monitor that string. With a alam and or ?

 

[dogman dan]

Definitely an option to just use a cellog 8. But now you are assuming that everybody uses RC lipo that has balance plugs.

Lots of people have some slas still, or a duct tape lifepo4, and don't have the cash for a Cycleanalyst for monitoring at pack level. This six buck voltmeter is an option for those folks.

I bought a couple primarily because both my CA's are 100v limited. And my racing bike controller feeds on 110v. So one of em can go on that bike since these go to 120v.

 

[parajared]

update: I gave hobbyking cellmeter 7 a try and it didn't work because the voltage display is static. In other words the information displayed only refreshes if you unplug the balance lead and plug it back in again. Unless you feel like plugging and unplugging the thing the whole time, it's useless as a voltage display. If anyone wants a cellmeter7 and you live in the united states pm me your address and I will send it to you for free.

Next I gave BVM-8S a try and it works great! You can display the total voltage from all six cells as well as individual, it has an alarm, the display is backlit so you can see it at night, it has a little battery % bar, and you can set so it reaches 0% at any voltage you want; I set mine to 3.65 volts per cell. If you are a hobby lipo user its a good way to go.

$8 from amazon.com
http://www.amazon.com/dp/B006TA2SBY/ref=pe_175190_21431760_M3T1_SC_3p_dp_i1