# Low voltage warning LED



## cagliari (Aug 9, 2010)

After building a CuLite style light a few months ago I have caught the bug  and I am now on my third light build. Thought I would go bigger and have gone for a Triple XPE powered by 4 18650's through a dimmable Black Cat 690mA driver. Would love to fit a battery status/low voltage warning LED but my knowledge in this area is sadly lacking. Any ideas guys?


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## jmitchell13 (Nov 20, 2005)

cagliari said:


> After building a CuLite style light a few months ago I have caught the bug  and I am now on my third light build. Thought I would go bigger and have gone for a Triple XPE powered by 4 18650's through a dimmable Black Cat 690mA driver. Would love to fit a battery status/low voltage warning LED but my knowlege in this area is sadly lacking. Any ideas guys?


Use a driver from Taskled: http://www.taskled.com/
The have the low voltage led function built in. You just need to wire a LED and set the voltage cutoff.

They cost a little more than the one you want to use, but IMO, they are well worth the extra $$.


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## whattingh (Jan 30, 2009)

here is something i have found but not tried yet
http://www.4qdtec.com/batty.html


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## cagliari (Aug 9, 2010)

The Black Cat driver, switches LEDs etc are built, tested and being put into the housing! Don't really want to spend more on a new driver, this one seems to give the output I need. The status/low voltage LED was an afterthought. Thought if there was a simple(ish) solution it would be nice to have. 
Cheers.


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## cagliari (Aug 9, 2010)

whattingh said:


> here is something i have found but not tried yet
> http://www.4qdtec.com/batty.html


Look like some good ideas. I can see the 1st circuit working with a few small changes. Will have to see if I can cobble something together and see if I can squeeze it into the can.
Cheers.


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## emu26 (Jun 23, 2008)

Haven't tried this one yet but I book marked the page for the next build


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## Pepster (Aug 21, 2010)

I am using 2x JUNSI CELL LOG 8S units - tiny - smaller than a match box and back lit - amazing units. and rugged.
http://www.hobbycity.com/hobbycity/..._Name=Cell-Log_Cell_Voltage_Monitor_2-8S_Lipo

These things really are the duck's nuggets. I log my cells voltage and down load it to my laptop after the ride - easy to see which cells are weaker than the others (and may need replacing !).

There are lots of cheaper units on ebay
http://shop.ebay.com/i.html?LH_BIN=...c=1&_sop=15&_trksid=p3286.c0.m14.l1581&_pgn=2


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## HuffyPuffy (Jun 9, 2008)

I was going to use this design for a battery monitor until I decided to use a microcontroller to monitor voltage.


__
https://flic.kr/p/2608325845

I posted some pics of it here.


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## cagliari (Aug 9, 2010)

Thanks for the ideas guys, not sure if any will fit inside the can but sure I will get something in the batt pack :thumbsup:


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## MrLee (May 28, 2010)

emu26 said:


> Haven't tried this one yet but I book marked the page for the next build


Great, I've just managed to scavenge the parts from a old computer board and setup to light at 6v gives a few minutes warning before power is cut out.

I'm going to put in a small trim pot to find the sweet spot on the discharge curve.


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## Pepster (Aug 21, 2010)

This one is getting good reviews on the RC forums:

Chargery Battery Saver BS6
http://www.chargery.com/cellSaver.asp


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## MrLee (May 28, 2010)

MrLee said:


> Great, I've just managed to scavenge the parts from a old computer board and setup to light at 6v gives a few minutes warning before power is cut out.
> 
> I'm going to put in a small trim pot to find the sweet spot on the discharge curve.


I got round to wiring up with a pot, the led starts to glow as it reaches the voltage, anyone know of an easy way to make it a harder cut in?


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## cagliari (Aug 9, 2010)

Pepster said:


> This one is getting good reviews on the RC forums:
> 
> Chargery Battery Saver BS6
> http://www.chargery.com/cellSaver.asp


WOW! looks like this is pretty much what I want. Audible and visual warnings and not too big. BUT can it only be used with a balance connector?? Does anyone know? My battery pack is made up with 4S LG 18650 cells in a 4 cell holder. Cells are taken out for charging so no balance connector wired in.


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## Toaster79 (Apr 5, 2010)

Wire your own connector and plug it in. I'm using BM6 on the same connector that I'm charging my 2S and 3S pack.


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## Pepster (Aug 21, 2010)

Toaster79 said:


> Wire your own connector and plug it in. I'm using BM6 on the same connector that I'm charging my 2S and 3S pack.


That is what I did. but... I bought some siht quality 6cell balance port extension harnesses and the intermittent alarm drove me crazy. Then I found some high quality silicone wire harnesses at my local RC store http://www.modelflight.com.au/ and every thing works perfectly now.

Once you have soldered a balance harness to your batt pack, you can use a $30 RC balance charger, (is the best method, and will give you 500 cycles on Li-ion) and leave your cells in the pack.

The RC guys discovered long ago that by not monitoring Li-ion/Li-po discharge (eg 3V min) and not balancing might give 20 - 100 cycles, vs properly monitoring and balance charging gives 500 cycles.


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## Pepster (Aug 21, 2010)

I just received an email from Jason Wang of CHARGERY "BS6 is not available, BM6 is suitable for you, correct?

If you agree, you can buy any products made by CHARGERY from me directly."

FYI


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## Pepster (Aug 21, 2010)

I have just ordered 2 of these:

RC Lipo battery monitor buzzer with LED warning light
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=270487655242

They are small. I will report on them when I receive them.


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## OldMTBfreak (Apr 8, 2006)

I found this post a while ago. http://www.rcgroups.com/forums/showthread.php?t=270580 I now feel that that balancing the battery is critical. Watching the battery charge and seeing the balancer led's react lets you see how "out-of-balance" the packs are. I also noticed that no matter how the pack was used, it ALWAYS charges out of balance!!! The balancer citcuit that Dan B designed has some cool features. One is that the balance transistor needs 1.2 volts to turn on, where as the transistor that turns on the led only needs .6 volt. So the balance led comes on before the balance function starts. I used a common hookup, so I can use my balancer on 3-cell, 4-cell, or 5-cell batteries. Here's a picture of a 5 cell battery fully charged.


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## bikerjay (Sep 16, 2007)

I have used these. These will work with out a balance connector. They are not the best since they only look at the packs total voltage rather than each cell. They sure are small and cheep though. They are also available in 2-5s versions for different packs. Really better suite for lipo but good lion too.

http://www.hobbycity.com/hobbycity/...5&Product_Name=Hobby_King__Battery_Monitor_4S

You can just stick it inside the light housing and wire it to the inputs of your constant current driver if you are using a simple on /off switch that breaks the battery connection to the constant current circuit.


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## brad72 (Jun 12, 2009)

Pepster said:


> I have just ordered 2 of these:
> 
> RC Lipo battery monitor buzzer with LED warning light
> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=270487655242
> ...


I have been using these for a couple of years now both in RC helicopters and bike lights and they are fantastic. At $4 off ebay you cant go wrong. Best part also is that the buzzer is about 100db so even if you miss the lights changing colour you won't miss the buzzer, unless you are deaf.


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## bbbbking (Nov 7, 2008)

take a look this one....not bad

47 x 32mm H10mm


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## Pepster (Aug 21, 2010)

Link ?


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## cagliari (Aug 9, 2010)

Pepster said:


> Link ?


What he said. This looks good


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## jspeybro (Aug 7, 2010)

cagliari said:


> What he said. This looks good


interested as well... link? specs?


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## Goldigger (Nov 6, 2009)

How bout one of these?
https://www.hobbyking.com/hobbycity/store/uh_viewitem.asp?idproduct=7390








https://www.hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=13276








https://www.hobbiland-rc.com/page7.htm


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## ZacAttack! (Jun 21, 2009)

I've built the first one of these: http://homepages.paradise.net.nz/bhabbott/lvw.html and it works really simply and well!


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## MrLee (May 28, 2010)

I built one of those two, had issues with it glowing so swapped it out to use a proper volt sense IC (MC34064P-5G) - http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=9666613


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