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JR-Spektrum . Gyro Hobbies . E-flite

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e-Align T-REX 250-450-500-600 > Lipo 80% Battery Monitor ?
 
 
MattC
Heliman
Location: Polesworth, UK

After damaging a couple of lipo packs by over discharging them I put together a battery monitor using a current transducer and basically summing the current pulled from the lipo, giving warnings when you approach the 80% mark but you do need a fully charged balanced pack for this to work.



The advantage of using a current transducer is you can also monitor the peak and average current, each time you land and hit the throttle hold and the monitor will show the peak & average. Upon spinning up again the peak & average currents values are reset allowing you to see which moves pull the most current. Stall turns into a strong wind seem to need a fair bit ! This also shows up any problems with wear and tear, the average current consumption goes up upon something wearing out, it saved me from a worn tail belt on my 450.

The unit has 8 leds each representing 10% of battery consumed, upon hitting the 70% mark - 7 leds illuminated, the leds will begin flashing and the flashing rate increases upto the 80% mark, past this point the flashing pattern changes to show you are damaging you lipo pack.

The unit is very small (32mm x 27mm x 3mm), current transducer (22mm x 24mm x 9mm) – not sure about the weight but it’s not much, it’s peak current consumption is roughly 0.1Amps (100mA) so it’s not much extra load upon your battery and it’s very bright, hurts the eyes to look at !

I’ve tried it out on a few trex450’s & 500’s with good success, the charger puts back what you'd expect for 70% consumed, I currently have two versions a 45 & 80 amp peak current aimed at the 450 & 500. I think I might need a few more mods for using with a trex600E but that’s to come

Finally to the question, do people think this a marketable battery monitor ?

I’ll put a short video clip together to show it working off the heli, will make it a bit clearer !

Cheers

Matt

Installed on my 450


I've changed the led's since this photo, for something 2 times brighter



EDIT
08-30-2008 09:01 PM
 
 
Boidman
Key Veteran
Location: home

That's slick as all getout, but of course there's at least one question.

If you could step aside and de-bias yourself for a moment . . .

So there's this new gadget out, like the OP posted, and another type that can have the alarming voltage set to almost any number one might want. When that battery voltage is reached, an audible and/or visual warning is given.

How would you compare the usefulness or benefits of one to the other?
08-30-2008 10:15 PM
 
 
leftyatm
Veteran
Location: Elkton, MD, USA

Very nice. Just something else trying to take my money...

2X T-Rex 450 SE V2 T-Rex 500 CF T-Rex 600 CF and T-Rex 600 NSP
08-30-2008 10:22 PM
 
 
MattC
Heliman
Location: Polesworth, UK

I’ve put together a video clip of it working, I’ve had to light the video with a desk lamp to make camera work properly – so it may have lost a bit of the intensity off the LED’s.

I’ve fiddled the software in the video, so it thinks 40 amps is being pulled upto the 70% point, then 20 amps from 70 to 85 % and zero amps from then on.

1. Self test on led’s for 1 second, flashing leds
2. Set battery size, 2000 mAH is selected – 0 to 4000 mAH is available.
3. Show battery percentage used, starts flashing at 70%
4. Flashing rate increases upto 80% then the flashing pattern changes – my camera’s struggles to keep up with this
5. Current draw drops, the peak and average current are shown.

This isn't the most exciting video but it gives you an idea of what it does

http://www.youtube.com/watch?v=sjb7ZvBV9L4

I guess there are only a number of ways you can indicate your pack is discharged but the big difference is that it doesn’t measure the cell voltage to determine the status of your pack but measures the current you’ve pulled from it, so you can give a more reliable warning that your near the 80% point - as long as you have a fully charged balanced pack.

So if you look at the following discharge curves, at 80 % discharged - pulling 22amps your cell voltages would be around 3.4 volts, if you suddenly pull 55 amps your cell voltages would be 3.2 volts getting very close to damaging your pack.



The other advantage is you have a miniature wattsup meter permanently strapped to your heli

Cheers

Matt

EDIT
08-31-2008 09:58 AM
 
 
leftyatm
Veteran
Location: Elkton, MD, USA

Nice work!

2X T-Rex 450 SE V2 T-Rex 500 CF T-Rex 600 CF and T-Rex 600 NSP
08-31-2008 10:20 AM
 
 
MattC
Heliman
Location: Polesworth, UK

I'm thinking of send one off to the trex tuning website to get an independent review but i need to put some instructions together first

Are there any other websites which give good reviews of heli kit ?

I'm pretty happy with the battery size range on the 450 version, 0 to 4000 mAh but i was wondering what size batteries are people using on there trex500's, is 0 - 4000 mAh ok ?

Cheers

Matt
09-01-2008 09:08 AM
 
 
tsekwe
Heliman
Location: Western Australia

Sounds pretty good to me Matt. My biggest battery for a 500 is 4000mah

Jonesy
09-01-2008 09:43 AM
 
 
Boidman
Key Veteran
Location: home

MattC, it seems you have a winner!

In my little corner of the world there are a few consistancies within a group of hobbiest that never really change much:
  • Some have to build or repair as fast as humanly possible, regardless their experience or knowhow.

  • Some are almost always absolutely certain of their electronic and mechanical setups, even with regularly poor performing helis.

  • Some have not and will never abuse their batteries, even though they seldom use a flight timer or track discharge and charge mAh or have even an occasional idea of battery temps. (puff/ignite)

A while back I got a helluva deal on a bunch of already cheap Li-Po alarms. They were added to new builds, or sold at cost, or given away to those who regularly killed batteries.

Somewhere along the way alarms became uncool or just not considered anymore. There does seem to come a point when guys eventually wrap there noggin around battery care, and an onboard device becomes less valuable, particularly when all methods of weight reduction can add up to a detectable benefit. But most of the alarms are really quite light and can be used at least during the early stages of establishing flight parameters.

Look to other message boards for a more-easy-to-promote-environment for new and potentially valuable devices.
09-01-2008 03:59 PM
 
 
cub2000
Veteran
Location: Massachusetts

Good idea Matt. When you have a mature product for the trex-600E, count me in for two.
09-01-2008 08:08 PM
 
 
ronmad02
Heliman
Location: Toledo, Oh - U.S.A.

Nice job Matt,

What are you going to look at for price? 450 size. Are you ready to sell now? The other question I am running 2200 mah on my 450 can you select the mah to the 100 or just the 1000?

once again nice job

ronmad02
T-rex 450sa
Swift 16
09-02-2008 08:31 AM
 
 
MattC
Heliman
Location: Polesworth, UK

Thanks for the encouragement, is nice to hear people would be interested in buying one

I'm happy that the 450 & 500 version are mature enough to sell but i need to write some instructions first, shouldn't take me long tho To give some re-assurance, I'm on the 3rd version of the hardware from starting to develop the software. I've been very careful to not sell something which will give me lots of trouble in the future !

How do people prefer instructions, technically biased or just plug this in here type thing ? My brother keeps reminding me I'm being too technical and you will loose a lot of people !

For the 450/500 version I was thinking of uk £40 excluding postage, I'm building these at home outside of work and is slightly time consuming but depending on demand I might get a company to manufacture them for me, which should reduce the price

The battery size is selectable in 250 mAh increments but with some judgement you can set any value inbetween, this may need to be different on the 600 version.

The 600 version shouldn't take me long, I've got the parts to build a prototype but i need a local volunteer to experiment on !! as i don't own a 600E - although it's a good excuse to expand the fleet I’ll ask around at my local club.

I have a few questions about 600's
What pack sizes do people use on the 600 ?
What speed controller sizes ?
What max current would be expected ?
What is the average current in a hover ?

Cheers

Matt


EDIT
09-02-2008 09:41 AM
 
 
Brunobl
Veteran
Location: Pomerode, SC, Brazil - 26 40S 49 11W

Hi Matt,

This seems like a cool device. But, I don't understand how you can directly measure current (as opposed to deriving it from voltage drop) with a device that is connected in parallel to the battery.

Where does the current information come from? Shouldn't a current transducer be in series with the battery to measure the actual current?

-------------------
Best regards,
Bruno.
09-02-2008 02:32 PM
 
 
MattC
Heliman
Location: Polesworth, UK

That’s the good thing about using a current transducer, it doesn’t interfere with the supply to your speed controller - instead the current transducer hooks over the positive lead to your esc before the battery connector. You need to remove your battery connector to do this but there is no electrical connection.

The current transducer works something like a transformer, working off induced current within a coil of the ct except it requires 5volts to power an internal amplifier.

Cheers

Matt
09-02-2008 04:43 PM
 
 
cub2000
Veteran
Location: Massachusetts

Quote 
I have a few questions about 600's
What pack sizes do people use on the 600 ?
What speed controller sizes ?
What max current would be expected ?
What is the average current in a hover ?

I'll answer a few of these questions for the majority of Trex-600 users who fly stock setup:

Pack sizes: 6s 5000mAh
RCE-BL75G 75A Brushless ESC
I'm seeing reports of people getting max amps of 93 and max watts of 1880 during punchout, though I've never meassured these myself.

You can probably go technical on your docs and let the gurus at trextuning or any 3rd party reviewers to do the more friendly step by step with pictures. That way you leave them some work to do with the free stuffs you provide to them
09-02-2008 06:42 PM
 
 
Brunobl
Veteran
Location: Pomerode, SC, Brazil - 26 40S 49 11W

Quote 
The current transducer works something like a transformer, working off induced current within a coil

Kind of like a clamp ammeter, then? Those also measure current without a series connection between source & load.

-------------------
Best regards,
Bruno.
09-02-2008 07:21 PM
 
 
efliernz
Senior Heliman
Location: Hamilton, New Zealand

A great idea BUT as you said, you need a fully charged battery. It also won't show (using current usage only) that a cell has started to fail with reduced voltage output.
I like an alarm that is bright and doesn't require thinking about or analysing while flying. Your voltage gets low, the lights come on so you land



Pete, Trex500, Trex600E, Streched 600, DSX9, DX7, Low-volt alarms - check the gallery for my alarms
09-02-2008 11:36 PM
HOMEPAGE  
 
 
MattC
Heliman
Location: Polesworth, UK

Its exacting like a current clamp meter

Thanks for the info on the 600’s, any idea what the average hovering current is ?
What size speed controller do people upgrade to on the 600, would a peak of 120A be more than enough ?

Using the combined cell voltage to detect the status of your battery means that battery voltage need to drop significantly to not get a false triggers on your alarm and on some lipo’s the voltage on the discharge curve is pretty much constant until you reach the 80% point which means you will damage your pack ! Especially if you need to fly your heli back from some distance.

Also using current draw to monitor the status of your pack means it doesn’t matter what combination of cells you have 3s, 4s, 5s… it doesn’t matter because your just summing current used

If you have a damaged cell in the pack you will have some warnings in how the model flies, lacking in power or limited flight time plus it probably time to get rid of the battery pack. The damage has either been caused by crashing or over discharging.

Why would you fly on a partially charged pack ?

This device works in the same way - fly, it starts flashing, you land without damaging your battery of course it’s your choice you can ignore the warning and continue flying !

Cheers

Matt
09-03-2008 09:07 AM
 
 
alvincfi
Senior Heliman
Location: Minnesota

Matt, when do you think you will have these available? Are you planning on selling them yourself or marketing the idea. Either way its a great Idea, count me in!!!

Also want kind of price are you look at selling these units?

Lepton | Evo 50 | Freya X-spec
09-04-2008 10:24 PM
HOMEPAGE  
 
 
MattC
Heliman
Location: Polesworth, UK

I have my first version of my instruction now, so i shall send a demo unit off for a 3rd party review by the trextuning website, see what they think

Your welcome to wait around to see what the review says but the 450 & 500 versions are ready, I will build them on demand as people want them - drop me a pm if you would like one

I was thinking of marketing the product myself, It will be £40 sterling excluding postage for either the 450 & 500 versions. The 600 version will be a little more as the current transducer i'm thinking of is a bit more expensive.

Cheers

Matt
09-05-2008 01:52 PM
 
 
ronmad02
Heliman
Location: Toledo, Oh - U.S.A.

So if I am doing the mathh right thats about 71.00 usd plus shipping do you know how much shipping is to the states?

Thanks

ronmad02
T-rex 450sa
Swift 16
09-05-2008 02:10 PM
 
 
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