Motorcycle float charger - Page 1
Forum section: electronics / projects

author: Harvs
author_rank: Super Contributor
timestamp: April 22, 2013, 09:22:09 am
content: So here's a relatively simple project I've been toying with for the last few days. Originally started out as just a series connection of LM317's as current and voltage limit, but it's relatively difficult (read expensive when you're building a few) to find low power adapters in the 20V range.So I thought I'd use some of the 5V 1A USB chargers that are starting to become all too common as smart phones proliferate.So this all works well on the bench. I've attached the schematic and output IV curve of the circuit. The 15-20Ah bike batteries I've tested all sit around the 30-50mA on float once fully charged.All the input protection has been thoroughly abused and everything appears to be holding up fine.Note that while the components on the schematic are what I used for a through hole prototype, the end result will be SMD so exact part choices still need to be made.So feel free to point out anything I've missed before I send the board off to manufactureCheersEdit: attached schematic with current sense on the correct side...

author: Harvs
author_rank: Super Contributor
timestamp: May 10, 2013, 09:23:07 am
content: And if anyone's interested, I finally got the laser cut sheet back to finish it off...

author: BillyD
author_rank: Regular Contributor
timestamp: May 15, 2013, 08:29:40 pm
content: Very nicely crafted. Well done.

author: Paul Price
author_rank: Super Contributor
timestamp: May 15, 2013, 10:26:29 pm
content: i've studied your schematic very closely and all I can say is that you should make sure you've taken your psych meds before you recheck your schematic or send it in with your printed circuit board order. How and why you are doing the things you are doing in your master plan(schematic) are more mysterious to me than my last Friday night's date with two devil worshiping nuns. Your prototype doesn't seem to be very neat looking but does not at all seem to match what your schematic shows...but that may surely be to your benefit.There are at least a few dozen more practical, simple, cheaper and easier ways to float charge 12V batteries. Solar cells would do it for free.Hint: People are always throwing away used 12V DC wall warts and they put out about 15-18V at 500mA to 1Amp or so. This is perfect for the job. All you need is one 2K pot in series with a (78L12) regulator's ground pin with to set the output voltage to 14.7V. If you want you can put a large (6A) power diode across the output to protect against voltage reversals and a small electrolytic capacitor.So, your whole float charge circuit can boil down to one(solar cell array) to four (78L12 circuit) components, total!

author: Harvs
author_rank: Super Contributor
timestamp: May 15, 2013, 10:53:36 pm
content: Quote from: Paul Price on May 15, 2013, 10:26:29 pmSo did that whole rant boil down to "you would have done it differently?"As to my schematic not matching what I've built?

author: c4757p
author_rank: Super Contributor
timestamp: May 15, 2013, 11:05:11 pm
content: Quote from: Paul Price on May 15, 2013, 10:26:29 pmHowand why? If you can't understandhowthat works you are in no position to suggest improvements. Do you attempt to give culinary lessons to the chef at your favorite restaurant? No, you sit down, shut up, and quietly shovel food into your maw, much to the relief of all the people who don't care about your suggestions.Also, it's rude to be rude.

author: Paul Price
author_rank: Super Contributor
timestamp: May 15, 2013, 11:19:19 pm
content: Sorry, I didn't mean to be rude. I was just responding your request "So feel free to point out anything I've missed before I send the board off to manufacture".There are more ways to skin a cat.There are many ways to do something, but the simplest and least complicated and cheapest and the easiest way, etc. would likely be the better way...why make things more complicated than they need to be? Isn't that something you could learn?If a cook at my favorite restaurant serves me something I don't like I have no trouble pointing this out, say my objections to the chef, the waitress and the owner of the joint and I would certainly refuse to eat or pay for it. It would no longer be my favorite restaurant.Don't shoot the messenger.Sometimes I feel that I might be am casting my pearls to pigs.