Home Brew Chargers anyone?

Why not use a flyback topology, with the battery connected between your

+V and the output? It'll give you 0 - whatever volt output, at the cost of having the battery floating above your ground reference. As long as you don't bring the battery + terminal above some magic regulatory voltage WRT ground (I think 60VDC or so is where some regulatory hurdles start popping up in most places) you shouldn't have problems.

.---------------------o----o -battery | | | | | --- | --- | | +12V | ___ | o----o---UUU----o---->|----o----o +battery | | gate drive ||-+ ||

Tim, Would this mess with the interface between the microcontroller, A-D, D-A, etc?

I got an idea from the flyback design. Using a Boost SMPS. If the Vin is from say 11V to 16V, any charging below 20V is charged between +Vin and

+Vout. Likewise, any charging above 20V would be charged between Gnd and +Vout. Or everything could be charged between +Vin and +Vout. Should be about the same as flyback but not inverted ... an inverted flyback! Maybe the inverted output wouldn't be difficult for the analog and digital interface, I'm just not used to working with the inverted, I'll have to think about it some more.

Thanks!

RogerN

Take a look at this one

It appears to be a super Alpha 4.

Join RCgroups and look in the DIY electronics forum. Several designs have been posted.

Mist use a commercial buck regulator chip plus additional smarts to condition the voltage/current/time regime. And of course a big fat FET or two to do the power side.

However, most people simply buy a commercial charger or three..they are not that expensive.

Thanks, I'll look on RCgroups DIY electronics forum.

I'm looking at several boost chips available and playing with circuits on Electronics Workbench and free SwitcherCad from Linear Technologies. I have a few inductors, microcontrollers, and MosFets to experiment with, I need to get a boost controller, Schottky diodes, and higher voltage capacitors.

I have commercial chargers but I don't have any that I can write custom programs for. Right now I would like to add a feature to keep liPo's at storage voltage and automatically charge them to be ready by the date and time I select(ie Noon Sunday, or next spring). I could do the electronics to make my Triton a 4 port charger but the program would have to be modified to switch batteries in and out of the charge circuit. Since the Triton, or any commercial charger I know of, isn't user programmable, I'm attempting to make one that is.

Thanks!

RogerN

AFAIK LiPos don't self discharge so couldn't I charge then today and have them ready next spring? That would be a good feature for Nicads and NiMh.

If someone could make my Dewalt charger a peak charger that drops off to trickle and runs from my truck that would be neat. mk

"MJKolodziej" wrote

My Dewalt charger is a peak charger, and I think it is a trickle charger, also. Yours probably is, if it is the kind that has a blinking red light when the charge is complete.

Don't be tempted to try and run it from a power inverter plugged into your truck. The inverter's instructions probably say to not use a battery charger that is a (some technical jargon inserted here that I can't remember) a high voltage, or something like that. The Dewalt chargers are indeed the type you are not supposed to use, and you may very well be rewarded by burning out your charger. Ask me how I know that!

The difference is mainly the fact that affordable chargers are square sine waves (they call them modified sine waves) and the type of voltage regulator in the inverter. They do NOT play nice together.

Also, things like air conditioners do not do well with cheap inverters. They will draw more than double their rated amperage, and that also may be fatal (if the inverter can keep supplying power without overheating and shutting down) if the inverter keeps running long enough.

The LEDs on my Dewalt charger do indeed change as per the diagram on the charger but I have employees who leave the battery on overnight or longer and the pack will be HOT to the touch no matter how long it's on. That is what makes me assume the charger continues to charge. I did notice they sell a car charger. Is anyone using LiPos on the tools themselves? I know we use them in planes. :) I may have to invest in new batts. mk

"MJKolodziej" wrote

Only way to know is to put a amp meter in line, and see what it is doing. I may do that tomorrow.

My theory is that it continues to charge at a much less rate, but more than it should be to be considered a trickle charger. Perhaps it is on full charge for the time period that the red light is on. (as it is blinking) That would make it perhaps a 1/2 rate charge, instead of a 1/10 charger that would be more appropriate for a trickle.

I have a dremmel cordless that uses LiPos, and it ROCKS! Lasts a long time, and has plenty of power. As an added bonus, I think dremmel finally learned how to make a good bearing, and how to balance their armatures.

If I understand correctly, a LiPo left fully charged for a year will only have about 80% of the mAH capacity that it used to. If the same pack was left with a storage charge, it would have 96% of the capacity. My thought was to leave it at storage voltage until shortly before use, hopefully maximizing the packs life. The storage voltage is supposed to be 3.8V per cell.

I have some Dewalt 18V cordless tools, I plan to try charging them with my Triton one of these days, my alligator clips will clip on their terminals and my voltmeter showed me the polarity. I guess you could take a fried Dewalt charger and use it for a cord to charge from your R/C peak charger.

RogerN

Jim, what are you trying to do?! mk I must resist buying new tools............

"MJKolodziej" < wrote

Sorry!

Naahhh, no, I'm not sorry!!!

Really, in all seriousness, I have to spread the word.

I am a real, real, tool guy. I LOVE my tools. I use them hard, professionally, quite a bit. (contractor) I can recognize a good tool, and hate a bad one.

THIS has become my favorite new tool. I use it constantly, for cutting missed nails while building cabinets. I sharpen tools with them. I engrave new tools with my markings. I shape wood with them, and sometimes cut steel to make jigs for other tools to shape wood. The imagination is the only limit as to the different things you can do with this baby.

I have had a few plug in dremmel tools, and always thought they were about half way to junk, but there was nothing better, for quite some time. I have had problems with loose bearings, and bad switches, and crappy chucks.

This tool has no cords needed, and I don't miss the cord, at all. No sacrifice in power, and seldom need more battery duration to complete a task. The bearings have not been a problem yet, and the chuck has not slipped or stripped, and the switch is still doing all of its variable speed tasks without fail or glitch.

I have had one problem. Nobody knows how to make a router or dermal or rotary tool shaft lock that will hold up to my standards of tightening a bit in the chuck. I HATE to have a bit vibrate loose and ruin what I am working on before I realize that it has slipped, so I tighten them down HARD. This shaft lock could not take it, and broke.

I removed it, but came up with a pretty simple work around. You have to have a new bit in your hand that you are going to install, since you are switching bits. Shove the end of the new bit into the shaft lock hole, and loosen the bit. Use the bit that came out to lock the shaft while installing the new bit. Not ideal, but it works.

As a model maker, you OWE it to yourself to get one of these things. It is ideal, and it will become your favorite new tool, too!

So again, not sorry. Git you one!

That is essentially true.

Earlier this year I checked out all of my LIPOS at the start of the flying season. Normally they are fully charged before being stored. All were about 95% of full charge or better.

They do self discharge, but extremely slowly. The problem is that they deteriorate faster when they are fully charged than when they are about half charged. Some chargers have a "storage charge" mode that charges them about half full and then stops.

Kong Power say you can also store their batteries fully charged in the freezer.

There is a relatively new technology available for NiMH. It reduces self discharge dramatically, at the cost of some capacity reduction, compared to conventional technology. These batteries go under names such as Sanyo Eneloop, Varta Ready2Use or Duracell Active Charge. I'm sure there are other brands as well.