"diode" mod for piccoz

ph2t · Post by **ph2t** » Sat Jun 09, 2007 5:21 pm

There is a small diode on the piccoz PCB that is put there to protect all the noobs from blowing their lipo if one was to plug the charger wire in the wrong way.

Diodes are used for many things in electronics, the simplest is their ability to only allow current to travel in one direction.

For you 'tronic deprived fellas, what this means is that for example, if you had a simple light builb (from a torch) and a battery, connecting the battery either way to the lightbuilt will result in it lighting up. Either way. This is because the lightbulb can except current in either direction.

Now if we put a diode in between the battery and the light, the light will still work, but only when the battery is connected in a certain polarity.

It's not rocket science, just like a one way valve on a LPG bottle you use for the bbq. t only allows the gas to travel in one direction, out of the bottle.

Now, all that shit over.................

The thing is this. Diodes take away approx 0.6V of voltage from the current source they are protecting against.

Eg: from above's example. 1.5V AAA powers up a light. Therefore the voltage at the light is 1.5V. Now if a diode is in between them, the voltage at the light is now (approx) 1.5-0.6 = 0.9V. The light is now "protected" against reverse polarity but at the cost of a 0.6V reduction in voltage.

So what does this mean to the piccoz? .............. here's a SIMPLe picture....

It is a simple picture, shit is omitted for simplicity.....

You can see that the PCB and battery are protected from reverse polarity here. Once the batt is charged, the PCB gets the full voltage from the battery since there is nothing in the way. The diode is used only for charging polarity protection.

Now, why am I writing all this..................

Here's the killa.

Looking at this circuit from the point of the charger, the charger doesn't "see" the battery natively, if only "sees" it through the diode. This is where the 0.6V drop comes into (very important) play.

Some of you may not know, but lipo charging is based on CC then CV. This means a constanc current to a certain voltage level then it goes to a constant voltage mode. I won't go into all this now, but I just wanted to highlight it.

As many of you know, lipos are charged effectively to 4.2V a cell. They run at 3.7V and all is good.

Ahhh, but wait. This 4.2V is to do with the voltage that the charger sees.

Now add the diode.

This is what happens.

1) plug charger in, process starts.
2) charger monitors battery level.
3) the level charger sees is actually (battery voltage) - (didoe).
4) eg: batt is charging and hits 3.6V, charger sees 4.2V (ie: 3.6 +0.6)
5) charging cycle finishes since charge reakons batt is as 4.2V.

Get my drift. The lipo is constantly UNDERCHARGED!

I tested this on my hobby charger. Connecting my ICE to the plug that goes into the picco, I set it to charge for 1S at 100mAh. (yes it's 2C but that's ok, won't blow the lipo up, will reduce it's lifespan, that's OK! lol...)

I only get approx 17mA into a 50mAh batt.,....

No, I removed the batt from the picco altogether and charged it directly connected to the ICE.

Now I get about 40mAh into it.....

Lesson learnt......

Bottom line, remove the diode out of the equation and you WILL get ore charge into the battery AND a longer runtime because of it....

I will post pics later. (8am here, bubs ain't woken yet......)

I'm yet to test this with the picco charger itself. But I'm confident I'm on the right track.....

Here's a pic of the diode in question. The plan is to remove it and just short the 2 pads. You now no longer have reverse polarity protection. But we're not noobs so it's OK!

.

ph2t.

sg219 · Post by **sg219** » Sat Jun 09, 2007 6:27 pm

Well, holy shit. Thats why it flies for a couple of minutes and dies. Its not fully charged!!

Clint · Post by **Clint** » Sun Jun 10, 2007 1:02 am

hot digity damn. GReat discovery.

Tana · Post by **Tana** » Sun Jun 10, 2007 7:15 am

Wow this is better than the Discovery Channel. Is the diode a surface mount or through hole?

Maxximum Attack · Post by **Maxximum Attack** » Sun Jun 10, 2007 8:51 am

GAH!!!
All these improvements AFTER I got rid of the damn thing!!!

ph2t · Post by **ph2t** » Mon Jun 11, 2007 12:15 am

Actually fellas, this is still just theory.

I posted this over at rcgroups.

http://www.rcgroups.com/forums/showthread.php?t=697540

Man 'o man, now there's peeps over there that really know their shit. Fuck! Even puts me to shame.

Clint, check out what they write over there. It appears that even the charger in the TX accomodates this drop and charges above 4.2V. So I may be onto a furphy here.

At the end of the day it may be a mod that's done that siomply allows you to charge the lipo from a proper charge instead of the inbuilt one. I don't know, still gots to test!

I'm happy I joined over there. It's refreshing to have other people talk about electronics at a level that serves my arse up on a plate, lol.....

Tana wrote:Wow this is better than the Discovery Channel. Is the diode a surface mount or through hole?

Surface mount mate. see the pic with the lil fellas circled in red!

Clint · Post by **Clint** » Wed Jun 13, 2007 12:53 am

are you able to check the voltage coming out of the charger during CV phase? if it's greater than 4.2v then you will know theres at least some compensation on the charger side.

I see you measured a .35v drop..the dude on rcgroups measured .15v.
if it sways that much across each heli, then maybe each tx/charger needs to be individually tweaked depending on the measured drop.
That could explain some of the vast runtime differences with the picco-z.

crazydave · Post by **crazydave** » Wed Jun 13, 2007 1:53 am

ph2t wrote: I'm happy I joined over there. It's refreshing to have other people talk about electronics at a level that serves my arse up on a plate, lol.....

Well I can barely follow you most the time, so you're definately my guru, but what I think is interesting is there was a couple points you said you didn't know, but I kinda already realized. Makes me think that its not so much that they can serve you up, just a different knowledge base. Everyone gots somethin' to learn from someone.

At any rate, they just look for reasons why it wont work. In my limited world of electronics, all I know is, hook it, and it'll either work or not. As long as nobody blows up, its all good.

hogjowlz · Post by **hogjowlz** » Wed Jun 13, 2007 6:31 pm

betty.k · Post by **betty.k** » Thu Jun 14, 2007 12:43 am