The Smallest Voltmeter

[dlb]

In trying to reduce the size of my launch box, I came up with this little critter. I call it " Micro VM "
about half the size of a 9 volts battery and is meant to test out those 9 volt batteries before installing them into the AV bay.
Most people have a full size Voltmeter and it takes up alot of room, more than I care to give up. Seems to be very accurate and the cost was small too, 5 to 6 dollar range.
Just trying to harden it, for just tossing into your flight box with no worries, has a 9 volt clip install on it to just clip and test, powers off the battery itself and provides a small load for the test.

A great space saver, want you think?

 

[sti_ffy]

In trying to reduce the size of my launch box, I came up with this little critter. I call it " Micro VM "
about half the size of a 9 volts battery and is meant to test out those 9 volt batteries before installing them into the AV bay.
Most people have a full size Voltmeter and it takes up alot of room, more than I care to give up. Seems to be very accurate and the cost was small too, 5 to 6 dollar range.
Just trying to harden it, for just tossing into your flight box with no worries, has a 9 volt clip install on it to just clip and test, powers off the battery itself and provides a small load for the test.

A great space saver, want you think?

Cute. I'd be tempted to install it in the avbay of my 4" rocket with a "push to read" button. Quick check of supply before launch...

 

[cwbullet]

That is awesome. Great idea.


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[g zilla]

Kinda cool but I think I will stick with my Fluke dmm as I can also check continuity and also more accurate.Also got my bow yesterday awesome

 

[Wayco]

A great space saver, want you think?

Think I want...
Put me on the list.

 

[cwbullet]

If there is a list, put me on it.

 

[Trooper]

Is this it?

https://www.amazon.com/DROK-Surface-Digital-Voltmeter-Detector/dp/B00C58QIOM/ref=pd_sim_e_1?ie=UTF8&refRID=0J0Z0BYM7W2WEMYNSTBB

Or maybe this?

https://www.amazon.com/KEEDOX®-Digital-Voltage-Voltmeter-Three-wires/dp/B00A722XGU/ref=pd_sim_hi_39?ie=UTF8&refRID=16PTWQSG7BV4GNF0B13Z

 

[dlb]

I really don't plan on selling these, just pointing out a good ,small and dependable VM , just for 9 volt batteries.
Chuck if you want one I'll make one for ya and bring to the launch. I'll show how I'm going to harden it, most likely potting it in epoxy.

Trooper those are very close, I got these from a friend in Thailand and only have a two wire lead, they are very accurate, fluke 123 said 9.21 volts and so did this unit. I like the fact it put a load on the battery, so no false floating voltage reading like on a DVM ( loaded tests are a lot better).

CHEAP , EASY, CHEAP AND CHEAP, I like it, if you miss place it or lose it you'll never feel bad.

Hey putting on a sled in the A/V bay is a good idea, think I'll do that

 

[cwbullet]

Thanks. I am interested is seeing how you harden ithe meter. What type of epoxy?

 

[oddmanrockets]

I just use the free voltmeters from Harbor Freight they work good and if someone borrows it and it doesn't make it ways back or if it gets destroyed from the desert heat sand No Biggie they always have a free coupon for another

 

[cwbullet]

I just use the free voltmeters from Harbor Freight they work good and if someone borrows it and it doesn't make it ways back or if it gets destroyed from the desert heat sand No Biggie they always have a free coupon for another

I have purchase and return 3 Harbor Freight volt meters. I finally gave up.

 

[sti_ffy]

Hey putting on a sled in the A/V bay is a good idea, think I'll do that

If you wanted to get really crazy, a rotary break-before-make switch could be used to sample the voltages of every supply in the avbay (each altimeter, tracker, etc). At the pad just rotate through the supplies to make sure all are well, then launch with confidence. You wouldn't have to actually mount the display itself on the sled, doing so might make it difficult to see the digit. You could have a small socket peeking through the avbay band. Plug it in, rotate the switch through the supplies, unplug.

What is the minimum operating voltage?

 

[blackbrandt]

dlb, I sent you an email about this.

This looks really cool!

 

[cwbullet]

DLB,

Have you though about a build thread? I am good if you show me how to make one myself.

 

[Wayco]

DLB,

Have you though about a build thread? I am good if you show me how to make one myself.

That and a link to where we could buy the module. Looks like the load is included in the module, so adding a 9v connector would be easy.

 

[billspad]

I don't know if this is exactly the same one but it's closer than Thailand.

I also bought them for checking batteries. I still haven't gotten around to putting a connector on the leads.

 

[dlb]

In looking around, Voltage range on the two wire version seems to be 2.5 ~30 volts
Their are two version, a two wire and three wire, on the three wire version you just tie +voltage and +power together.
with it being 2.5` 30 make for a nice range usable in rocketry, covers from LIPO's to launch batteries with ease.
I looked on Ebay with the search for " LED voltmeter " and hit a bunch of them, ranging from 1.35 to 6.00 dollars.
But I know not of those as far as accuracy, just the (5) I've tested from my friend.
I just like that powering the unit supplies a small load ( mostly thru the LEDS ) to the battery under test, can't tell you how many people have been faked out with a DMM ( battery with no load tends to float back a good reading and are NOT, but under a load show they are not good and start dropping voltage quickly).


I'll show in a day or so how I make and harden them for range boxes. It's really easy to do, only two things to solder.

 

[cwbullet]

Awesome. I will give it a try.


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[Wayco]

How much of a load are your units adding? Could you take a resistance reading across the leads?
We might be able to compare your units to the ones Bill has found. If I just need to add a big resistor across the leads, that sounds doable.

 

[billspad]

The ones I have measure around 108K ohms across the leads.

I'm looking forward to see how DLB hardens them because mine have been sitting on my bench waiting for inspiration.

 

[CCotner]

The title of this thread sounds like an awesomely nerdy children's book. =p

 

[dlb]

resistance won't work, although my measures 110K, very close, but like I said, don't matter, when the unit powers up and lights the LEDs is the big one, mine measured to 15ma draw @ 9.2 volts. looks to me like the LEDS draw about 2 ma per bar on the display. But that itself is enough of a draw to remove most floating battery problems, by my calcs anything above 3ma. works good.

put a well used battery on this tester that the DMM(Fluke 123, for those how would ask) and it said 8.9volts, well I knew that was wrong ( had 5 flights on it and about 1 hour of NiteBow usage.) I was expecting 7.5 volt or there abouts. hooked up mr. Micro VM and got 8.7 volts, no ,8.2 volts, no, 7.9 volts and kept on dropping in front of my eyes down to 7.3 volt and stabilized ( took about 10 seconds, but in watching it drop just proved the batteries weakness.

So I say plug it up and wait 10 seconds for the battery real reading, brand new out of the pack battery measured at start 9.23 volt and fell to 9.21 in 10 seconds, your good, NEXT!

5 dollar comfort in a box, cheap insurance.

 

[billspad]

MPJA has the red ones on sale for $2.45.

 

[Wayco]

Thanks Bill, I picked up a few of these, let you know how they work for me.

 

[cwbullet]

I received a couple types today. Some of them are pre hardened . The green is easier to see.

 

[JDcluster]

How about these?

https://www.ebay.com/itm/New-High-Q...005&prg=9374&rk=2&rkt=6&sd=281294886758&rt=nc

Is there a way to install a momentary push-button switch so that: it will only activate the display when the switch has been pressed?

JD

 

[dlb]

Well it took awhile.
Just got back it to it.
After trying multiple methods on hardening these little critters, from Epoxy to baby boxes with no success, I talked to Chuck (CWbullet) at a launch and he tried heat shrink tubing, Smacking myself in the head I tried it, it worked!
I used (1) small tie wrap to secure the battery wires to the meter and 3/4 " heat shrink tube, and heated up the end to waterproof it a little too, by crimping the ends(needle nose pliers). In doing so I found the wire casings even got melted a bit and sealed in too! water tested it, AKO.
still small and now can take the beating of a range box with ease.

And under 5 dollars

Thanks Chuck!!!

 

[cwbullet]

My pleasure. I had another project I was shrinking and it made sense.