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mora 11-19-2009 05:31 PM

PCB design for led bargraph battery monitor
 
Hello everybody.

I've been reading these forums a bit and I thought I could share something with you.

I noticed cool monitoring system in Forkenswift project and decided to build one. The original led bargraph battery monitor story was posted on evconvert.com in two parts. Link to first part here and second one here.

Original design is very simple and functioning. It was build on a stripboard which I didn't like much. I asked one of the commenters for a pcb he had designed and got it, but it was faulty. One of comments included design for 12V but there was no pcb design for it. Emailing others for design sounds a hassle. I made a pcb design and that's what I'm willing to share.

You can find it in .pdf format from
Index of /huski/paskoo/led_bargraph_battery_monitor_12V

Voltage range for this design is from 10.3V to 14.7V. Lowest led lights up at 10.3V and highest at 14.7V and stays lit if more voltage is applied. I'm not electrician or designer but could do pcb drawing. I made four of these myself and tried one straight out of car 12V battery. Voltage sagged to ~10.5V while igniting and jumped right to ~14.5V when motor started running. This design works at least.

I made also sleek design like the original was. I haven't built it yet but I will do so tomorrow. It is as tall as led bar so should be easy to glue led bars together. I'll post pictures and a video when done with testing.

I was going to post this as a reply in original page but didn't figure out how. Forums are easier, hehe.

http://koti.mbnet.fi/huski/paskoo/le...or_12V/top.jpg

mora 11-20-2009 05:08 PM

PCB version 1.1 confirmed as working one too. Now I need to make 9 of those for 120V system (10 x 12V)

Video available here:
http://www.youtube.com/watch?v=TQq-yfw0pUk

atfab 12-06-2009 11:40 PM

DC Voltage Monitor Kit - VM-1 - Electronic Hobby kits from Electronic Rainbow, Danville Indiana

dcb 12-07-2009 12:17 AM

I do like that Mora has published a schematic, and has the part count is down to 9 components + low profile. The parts are prolly $5 so if you wanted to monitor your EV batteries in the pack independently then you can stack these pretty nicely.

Just not sure how you turn them all off when the key is off :) Might need a couple more components for an "enable" that gets pulled to ground or so.

Daox 12-07-2009 06:56 AM

Someone in the local EV club is working on a system to do that right now.

dcb 12-07-2009 09:24 AM

Worth noting that a $10 LCD 2x16 display can do bargraphs too:
http://lh6.ggpht.com/_ERCBSb5GqMU/Sh...0/IMGP6866.JPG

could be arranged into 32 little graphs (8 bars hi) or 16 taller graphs

I like the 16 small graphs (or however many batteries you have) on top with text on the bottom for something like total pack amps and volts or something.

mora 12-07-2009 11:45 AM

Now that's a great meter, dcb. Wish I had some programming skills to do the same.

I didn't even think about shutting down all the meters until last week. Maybe one mainboard with in/out-connectors for each battery and simple transistor-switch for each circuit. 12V input for main board controls all the transistors at once.

I'm no electric designer so it might take a while to implement one. But I'll do one before our ev conversion project hits the road for first time.

dcb 12-08-2009 10:51 AM

I had been toying with that idea for a while, but that was skelly who actually made that graph
http://ecomodder.com/forum/showthrea...-etc-8695.html

But still challenges remain for a whole pack battery gauge for it also :)

Tweety 12-08-2009 06:52 PM

First of I'm a newbie on this forum, so I really don't want to step on any toes, I kind of plan to pick your brains on EV's as much as possible... Buuut... Since I'm kind of good with designing circuits, I kind of think I can add something... And the circuit here has a little design flaw... Not something that makes it not work in normal operation though...

Mora... A few questions on the design... The diode D1, what is it supposed to do really? Cuz right now it's not really doing anything a normal wire couldn't do...

My guess the intention is to protect the circuit? Ie swap ground and +12V and nothing goes poof?

Then it really should be connected to the ground wire... Facing so that the ground flows out of the circuit is open, but nothing goes in that way, since that is what makes things go poof... Connecting ground to +12V won't make anything go poof... It just won't do anything hooked up that way, no lights, no magic smoke...

Another thing to remember when doing protection... In this instance it's kind of an moot point as the protection doesn't really do anything as it is anyway, but right now R1 is connected to the "outside" leg of the diode... Ie even if the diode in theory would protect something the R1 would still give a path to destroying stuff when connecting things up the wrong way...

And unfortunately two wrong does not make one right...;)

Move the diode to the ground connector and have it block the path into the circuit and it gives protection... As it sits now you can just replace it with a wire and the circuit will work the same...

Tweety 12-08-2009 06:57 PM

Oh, for a shut off circuit I'd say the idea of a "backplane" with a simple switch operating all the signals is a good one... It won't really by many components...

mora 12-09-2009 03:21 AM

Quote:

Originally Posted by Tweety (Post 145868)
The diode D1, what is it supposed to do really? Cuz right now it's not really doing anything a normal wire couldn't do...
My guess the intention is to protect the circuit? Ie swap ground and +12V and nothing goes poof?

Hey, glad to see you in this thread. You definitely know these things better than I do. I appreciate your time you spent replying.

Actually, I was wondering the same when I saw the circuit for a first time. I thought I could leave it out but kept it since I don't know if it has some meanings as protection. Remember, I have done nothing but placed components on a pcb. Didn't even pay a thought but I guess I really should have. Original one was on simple board with tin/wire bridges all around. Schematics are also made by the same guy. I should ask him what he was thinking when placing that diode there.

Quote:

Originally Posted by Tweety (Post 145868)
Then it really should be connected to the ground wire... Facing so that the ground flows out of the circuit is open, but nothing goes in that way, since that is what makes things go poof... Connecting ground to +12V won't make anything go poof... It just won't do anything hooked up that way, no lights, no magic smoke...

Move the diode to the ground connector and have it block the path into the circuit and it gives protection... As it sits now you can just replace it with a wire and the circuit will work the same...

Now I see, maybe the original plan was to do so, to prevent connecting meter reversed. Simple protection.

Tweety 12-09-2009 12:54 PM

1 Attachment(s)
I did this on my break today...

The actual PCB won't be of much use as it's SMD and dual layer, but the schematic shows where to put the diode to have it actually protect something...

And I added a transistor and a couple of resistors, making a simple remote on/off switch... Just add a +12V wire to a single switch for all the boards... Since you are using through mount replace the SMD BC847 with the BC547 instead...

R7 is used as a jumper, place a wire here and you can use the board without the transistor and it works as your previous boards, leave R7 off and add the transistor and R6 and you can hook up the switch and stack them...

The jumper JP1 is to set Bar/Dot mode... can also hook the wire coming out to +12V and it does the same... (I'm going to pot mine in, so I needed the jumper...)

dcb 12-09-2009 12:58 PM

can you expand on that pic, i.e. add a small battery pack of 3 12v batteries and 3 led monitors and show what goes where?

Tweety 12-09-2009 01:02 PM

Hm... Ok... How about I label stuff a bit better...;)

dcb 12-09-2009 01:03 PM

x

Tweety 12-09-2009 01:12 PM

1 Attachment(s)
Same circuit, better labels...

The things that have changed from mora's design is the diode and the 4 input terminals...

The four connections the left are inputs... Ie either a wire or on my PCB I'm using a set of four screw terminals...

Moved the diode to the negative terminal...

Added the transistor and two resistors at the lowest terminal... You use either the R7 alone making this circuit behave exactly like mora's (except for the diode)

OR the R6 and transistor and then you use a switch and sent +12V to each of these terminals and all boards switch on...

Tweety 12-09-2009 01:23 PM

To make things more understandable... What you need outside the picture...;)

Hook each battery to the positive and negative terminals... One battery to one monitor... just like mora...

Then, assuming you are using more than one in a stack hook the enable pins of all boards to one switch and supply that with +12V (from you aux battery or such)... That switch now switches all the monitors on or off... (The drain on the aux battery is somewhere around .02 mA per monitor or so, so not really noticable) and once off it's disconnected from all batteries so no parasitic drains...

The Mode connector can either not be used and then you solder (or not) the internal jumper to set the bar/dot mode permanently... Or you hook this to a switch with +12V and you can now select mode as well...

dcb 12-09-2009 02:28 PM

Like I said, It would be nice to see several attached to a small stack of batteries, that is the tricky bit. Not sure your enable is above the rail in all cases, but putting these in context of the whole might make it more or less evident.

mora 12-09-2009 04:17 PM

Now that's great. I made the diode correction to single layer pcb file but didn't upload it yet. Hook up enable switch to 12V system and led meters turn on as you turn the key.

Tweety 12-09-2009 04:30 PM

Don't worry yet... I'm still thinking... I just came up with a scenario where that screws up the readings... So I'm back to the drawingboard...

Tweety 12-09-2009 04:31 PM

Plus we are going for low cost aren't we?

Tweety 12-09-2009 04:58 PM

1 Attachment(s)
I love optocouplers...;)

Especially cheap one's...

Now this should be bulletproof... Not even I could screw this one up...;)

dcb 12-09-2009 05:36 PM

I can't tell if there is a lower cost option for the opto, since we are just looking at a single tree in a forest here, but the opto should do it, same circuit as the original with an opto enable.

yah, the GND should be connected to batt neg? Don't want it to go to vehicle GND on accident.

The R7 looks strange though, like it is always "sorta" on.

Tweety 12-09-2009 06:06 PM

The GND in the schematic is internal, the only thing connected to anything is the 4 posts on the left hand side... Connecting to vehicle ground wouldn't really harm anything unless that is connected to pack ground... Otherwise it should be the same as negative on the 12V system...

The enable pins, two this time is +12V and ground in the 12V system...

R7 is a bypass... If you use the remote on feature you leave R7 out of the circuit, if you use it as a standalone, you stick a wire there and leave out R6 and the opto... It's an easy way to have one PCB for two functions...

The opto is about ~$0.5 in batches of more than 10 from my local supplier, so not too expensive... Dunno what you would pay/get... But it should be more than possible to find an equivalent cheap one...

dcb 12-10-2009 01:40 AM

Quote:

Originally Posted by Tweety (Post 146180)
Connecting to vehicle ground wouldn't really harm anything unless that is connected to pack ground

yah it will, you really need to look at the bigger picture :)

mora 12-10-2009 09:06 AM

So there was a problem with transistor. Optos are even a bit cheaper here than transistors. And yes, at least I aim for going cheap.

Tweety 12-10-2009 09:42 AM

Quote:

Originally Posted by dcb (Post 146316)
yah it will, you really need to look at the bigger picture :)

Dammit... I'm still thinking car = 12V... ;)

Ok, taking a few steps back I get the picture... Now I'm gonna upgrade my 1n4001 diodes to atleast 1n4004's... should give me enough protection to realise I made a bo-bo before I let out the magic smoke...;)

Tweety 12-10-2009 09:45 AM

Quote:

Originally Posted by mora (Post 146354)
So there was a problem with transistor. Optos are even a bit cheaper here than transistors. And yes, at least I aim for going cheap.

No, not really a problem... It's just that when using a transistor it would end up needing a few more components as well... And since an opto is atleast in the ballpark same cost and in the end doesn't need any more components to do the job... Well I adhere to the KISS principle...;)

MrOrange 10-20-2011 10:48 AM

Hey guys,

I've been looking for an LCD battery monitor display for quite a while now. It seems every time I find one, it was developed in 2008/9 and has since been abandoned. I have attempted multiple times to contact many manufactures with no replies. One such display is: www(dot)youtube(dot)com/redirect?q=http%3A%2F%2Fevie-systems.com%2Findex.php%3Fmain_page%3Dproduct_info %26cPath%3D44_48_49%26products_id%3D65&session_tok en=VARP0DJz2ydFO0eiQgzjVLNciTh8MTMxOTIwNzk1MkAxMzE 5MTIxNTUy

I am going to have 60 cells in my EV, so the available LED monitors while cool, aren't really practical. Does anyone have a lead on such a system? I have never worked with LCD's before so I know I cannot design one, but if someone here could I would be happy to throw some money behind them to assist development.

I think with today's systems and higher voltages this would be more in demand than it is. Surely it's going to be highly sought after in the coming years.. Or is there a system I've been unaware of at the present time?

Does anyone agree or am I crazy? Sorry to bump old thread, cannot make new post..

mora 10-20-2011 10:56 AM

I abandoned the idea of using this LCD monitor mainly because I abandoned Pb-batteries. Luckily I made only a few for testing purposes. They worked fine.

But I'd like to get similar monitoring system as you described. Small and simple bar display which doesn't show volts but a rising/lowering bar which is related to voltage level. One could easily tell which cell sags the most. I believe it could be a simple loop-style wiring with no spaghetti involved if using canbus. It could even be integrated into miniBMS or such system. Two wires running from module to other and only two wires running from pack to master module. No high voltage either.

MrOrange 10-20-2011 11:02 AM

You have made a good point, perhaps we should take this to miniBMS and see if this is something they are willing to work on / integrate. This would be an excellent addon feature for miniBMS.

I know the LED monitors work great, but try mounting 60 of them on a dash and have it look good.. Not to mention the mesmerizing light show at night! haha


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