My homemade volt meter

NormL1

NormL1

Member
I can't stand idiot lights and the view from my Izip Express isn't good. I am a big guy and the idiot lights are way low from the horizon, so, I had the idea to make my own volt meter. Now that I have done it, I know one of you is going to say, "why didn't you buy this thing over here?", ... well I couldn't find anything that would work.

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I could not find a meter that would measure the needed voltage range just powering from the voltage, so, I found this volt meter on eBay (Link Removed - No Longer Exists). It requires 3.5 -24volts to power, so, I had to place a step down regulator in front of it. I used this one (Link Removed - No Longer Exists) I modeled up a case from the dimensions and the pictures on eBay and ordered it from Shapeways.com. Well when the meter and the regulator arrived from China, the regulator didn't match the picture at the very important mount points. The meter was a perfect fit. I had anticipated some differences with the regulator and had made it more of a clamp mount, so, it was fine.

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After soldering the leads on the regulator I had to cut them with a box cutter to get them flat enough for the clamp mount, but, that was the only real compromise because it didn't match the picture.

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I dyed the case black as I had it printed in nylon. My guess it that I will be taking it apart and painting it in a couple of years, we will see.

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Since I am getting voltage from the charging port, I needed to place an on / off switch in. If I didn't it would always be on.

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I have printed a couple of GoPro mounts for my track car, so, I knew that I needed to match the curvature of the handlebars and glue a piece of inner tube to it. Once zip tied down, they do not move.

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Fired it up in the garage

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Now the BAD part. Yes, I forgot how washed out red LED's are in sunlight. This thing just turns invisible ...

This is looking into the sun. Yes, it is actually in its own shade ...
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This is the sun (at least in the Pacific Northwet) beating down on it
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When i was wiring it up I found that I needed to take the bike to the solding station to finiah. I found I can make it clean if I slide the wire down next to the frame up right, but, it can only be bare wire. I didn't want to drag it up stairs, so, I cheesed it around the motor.

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Prototype one is a failure only because you can't read it. Basically I have two voltage gauges I can't read now .... LOL
 
You must put out massive power if you need the 100 amp! Just kidding as I know you were probably thinking better safe than sorry. I should have it by Monday and then I can design a quick little case / mount for it and wire it up. My thoughts are in the center of the bars like the Rad Rover King-Meter SW LCD. Like you, I want to know what is going on! Thanks for your input
 
George, I have the part. Can I assume that you never really have to touch it once it is set up? My thought is a case with a clear plexiglass face and an on/off switch down low and too the side, but, if you have to mess with it, that would not work.
 
Norm,

The meter I have works in a way I don't like too much. It saves the data for the watt hours. If you run up 300 watt hours and disconnect the meter and it goes dark. Plug it in again and the 300 watt hours are still there. For now, I would rather zero it out, and that means pushing the little button on the front. If you don't care you could cover it, but otherwise you might want to drill a little access hole there.

On mine you can set the high and low voltage alarms if you hold the button down. If you just press the button, it turns the light on and off. If you hold the button for a long time, you can clear the watt hours, but you have to press again.

It's in the instructions. I assume the meters work the same.
 
OK, I will give up the water resistance for now as I don't ride in the rain anyway. Kind of sucks a bit on the wattage re-set, but, it was the instantaneous use that I was more interested in. Still better than a big red meter you can't read ...
 
I used it with a cell phone mount today. Easy to read, all the right information. I might carry a plastic bag to wrap it if it looked like rain, or unplug it.
 
Well, I now know that my system shuts down at 30.7 volts .... I like that they choose a higher PCB shutoff than I am used to seeing percentage wise. If you read the Li-ion information you would conclude that you can discharge below 30 volts for a pack this size. The significant drop curve appears to start around 34.0 volts. I use Li-ion and LiPo all the time in a different industry and am just not comfortable getting those last bits of voltage. Especially since there will not be much amperage there as well.

George, I am running with your idea. A simple case with an edge that clamps down on the face of the instrument. This will allow a piece of heavy sandwich bag to be used as a windshield. I also want to bring the button out and widen it for use with gloves if necessary.
 
I did find that I can buy small sheets of Lexan at the hardware store. They all seem to be 0.093 in thick, so, I inset an area to silicone in a Lexan window 44.5 mm x 65 mm and I didn't have to make it taller. With the very short throw front push button with lithium grease (very high melting point) in the cap and ridges in the main seal, this won't leak. Yes, I went from not caring if I could use it in the rain to making something I won't be concerned about. That is the nature of 3D design, LOL, you can't stop fiddling. I am ordering from Shapeways today http://shpws.me/M2EW
 
We will see ..., my great fear is that the Lexan will reflect light in such a manor to make it hard to read.
 
I have two of the 100 amp meters on ebikes now. The shunt is large, but it is easier to run small wires around the bike, from the shunt. This is the only meter I have found that continuously shows everything you need, and it is very readable. Maybe you could get a nice mount package and sell it to the DIY stores. For the price, I am going to keep a couple around. Hope the cover works out. Sounds like you know what you are doing.
 
You have an excellent point regarding the smaller wires for a remote shunt. Well I don't think this design precludes the use of the remote shunt version, as it sure looks like they all use the same case. I know enough to be dangerous with electronics, but, what I know tells me that I have forced myself into a situation where the size of the wire I run for the shunt will effect its accuracy. 20amps to the meter do sound like thick wires now that you mention it. I may move over to your way of thinking with the remote since they are fairly cheap. These cases look like they are going to be around $62 after I add a $10 spiff for me at current printing prices. I am not going to make a kit though. I do have a stack of the on/off switches, an old inner tube and a sheet of Lexan, so, I could make a couple of accessory packs. I have lost 30lb since buying the bike and this is just part of my over exuberance.
 
NormL1 said:
We will see ..., my great fear is that the Lexan will reflect light in such a manor to make it hard to read.
Click to expand...
You can get clear non-glare acrylic and polycarbonate (Plexiglass and Lexan). Most plastic supply businesses will sell off-cuts, so no need to buy large sheets.
 
I just did a research binge on the Internet and there is a lot to know about poly-carbonate. Now that I am a couch expert on the stuff, I am going to score and break it like I first thought, but, with the knowledge that it is going to be way harder than I thought.

J.R. we do have the plastics company's like you reference, but, they are all up in the horrible traffic areas that are to be avoided at all costs. Hopefully it isn't a glare monster, but, I did see that I can buy thinner sheet on line and non glare as well. Thanks for the comment
 
NormL1 said:
I just did a research binge on the Internet and there is a lot to know about poly-carbonate. Now that I am a couch expert on the stuff, I am going to score and break it like I first thought, but, with the knowledge that it is going to be way harder than I thought.

J.R. we do have the plastics company's like you reference, but, they are all up in the horrible traffic areas that are to be avoided at all costs. Hopefully it isn't a glare monster, but, I did see that I can buy thinner sheet on line and non glare as well. Thanks for the comment
Click to expand...
You can get polycarbonate as thin as business card stock, but that'a more of a specialty item. It's fairly common to find thickness down to 1/16". It can be readily cut with most types of saws and routers, acrylic cuts better via scoring since it's more brittle. If you do use non-glare, look at it closely as it's only one sided. Also never use any glass cleaner on clear plastic, use isopropyl alcohol or mild dish detergent.

Good luck with your project, I'm enjoying your thread!
 
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I opened the meter for two reasons, 1 to see if much would be gained just by re-casing the board and 2 to see if I could remove the 20 amp shunt for relocation. Not being able to see anything that isn't obvious on a circuit, the shunt is invisible to me. I do think a substantial amount of height could be removed by de-soldering the terminal block and replacing it with wires. I already have this one in print, but, if it fails, it is going to get smaller.

On the wire sizing note, using this website http://www.solar-wind.co.uk/cable-sizing-DC-cables.html I come up with 18 gauge wire for 1 meter, 20 amps, 36 volts and 3% loss, 16 gauge for 2%. My issue is I don't have a clue how much loss is acceptable. My guess is that a meter needs as little loss as can happen, but, that the loss would be relative so the brain would adjust.

I decided that I would rather have a very small 2 pair wire on the frame so I ordered the Drok incorporated with the 50 amp shunt
 
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