how to build a 12V input 24V (29V) output charger

12 posts / 0 new
Last post
terramir
Offline
Last seen: 5 years 9 months ago
Joined: Monday, July 21, 2008 - 18:09
Points: 33
how to build a 12V input 24V (29V) output charger

How would I go about making a simple circuit that could let me charge my 24V batteries with my 12V solar panel storage? well 11V to 15V depending on charge level and time of day. I need like 29V to charge a SLA 12V pair right?
anyways anyone here an electronics crack that would know how to build something like that as simple and cheaply as possible?
terramir

reikiman
reikiman's picture
Offline
Last seen: 12 months 2 days ago
Joined: Sunday, November 19, 2006 - 17:52
Points: 8447
Re: how to build a 12V input 24V (29V) output charger

There's a couple things to think about ...

One is that placing solar panels in series the voltages add.. just like when you put batteries in series. So if you had two of those panels they'd produce 24v (in series), three would produce 36v (in series). I suspect (but don't know) that the actual voltage might vary based on how well exposed to the sun they are. Or maybe what would vary is the amperage? Dunno.. haven't played with solar panels to see how they actually behave.

Another thing is that a battery charger does more than just funnel electrons into a battery. There are little elves inside the charger who are constantly sampling the voltage and determining with their elvish sense when the battery is fully charged. There are such things as charge controllers which are meant to be used with solar panels to charge a battery pack.

terramir
Offline
Last seen: 5 years 9 months ago
Joined: Monday, July 21, 2008 - 18:09
Points: 33
Re: how to build a 12V input 24V (29V) output charger

Oops totally misunderstood me u did. What I want to charge are the SLA from my e-bike with my 12V battery bank (230Ah bank) that is being charged by my solar panels. My batteries that are being charged by the solar panels needs no controller, cause the max current is less way less than 5% C the math works out to less than 2% of C which is like a low float charge, just a diode to prevent reverse panel heating at night.
What I need is a constant voltage constant availible current boost charger that will boost the 12V from the bank (10.5V-15V) to 29V. Because of ohm's law and a more than theoretical internal resistance of SLA's the lower the voltage differencial becomes the less current will flow. once the SLA's reach 29V the current will stop period. Cant charge without voltage differential. However the voltage will lower after a while and then charging will begin again unless I add a simple circuit to shut it down will have to figure that one out :p
terramir

Ray_T
Ray_T's picture
Offline
Last seen: 15 years 7 months ago
Joined: Monday, January 29, 2007 - 08:56
Points: 35
Re: how to build a 12V input 24V (29V) output charger
terramir
Offline
Last seen: 5 years 9 months ago
Joined: Monday, July 21, 2008 - 18:09
Points: 33
Re: how to build a 12V input 24V (29V) output charger

that would work but I dun have that kind of money laying around :( would take me 7 years of charging my bike to recoup the money in electricity savings. :p And considering then I'll use the electricity from the solar panels through my breaking down inverter (like 50% efficency now) for other things like watching tv I'll save on that instead so overal recoup time of that price about 20 years :p
Ty though for the link but I wanna find a scematic I can build myself mostly out of salvaged parts :)

terramir

Brock
Brock's picture
Offline
Last seen: 12 years 5 months ago
Joined: Thursday, August 16, 2007 - 19:27
Points: 87
Re: how to build a 12V input 24V (29V) output charger

These aren't the cheapest either, but I think this is what your looking for.

http://www.solarconverters.com/product_frame.html

12v in and 24v out, they stay in relation to one anohter, so if your charging at 14.2v, the output will be up at 28.4.

fabelizer
Offline
Last seen: 15 years 6 months ago
Joined: Sunday, August 10, 2008 - 08:29
Points: 5
Re: how to build a 12V input 24V (29V) output charger

It sounds like you want a DC-DC Convertor to boost voltage level. Like any conversion, there is a net loss due to conversion, but it is quite possible to do. There are some products available in modular form, but you still need to control your charge levels after making the voltage conversion. You are taking on a considerable project as I have seen nothing on the web that indicates someone is already making a product that provides a solution for you. I don't think you can hack into a smart charger to get the back end controller you need, and though they could be designed on the front end to run on a lower voltage (and DC which is no issue), again, I haven't seen that solution offered. You would basically have to design and build one from scratch....best of luck, and when it's done, be sure to advertize it!
Your only viable comercial option I've seen at the present time is to run a stock smart charger off a stock AC invertor....not very efficient, but available...
There are some small (300W) invertors available for running laptops in the RV and what not, that you could just plug a charger into. I think you can ebay them at $30 or less, and you already have the charger. If you are charging a 24V pack at 2A now, then a 100W invertor is twice as big as you need. This route is the least expensive, and certainly not too inefficient. Don't expect to charge overnight and run other stuff too, this would take a bite out of your AH. It might hardly be noticed during a sunny day though, as usually there is more solar energy available from the panels then the batteries can use to make up for slightly overcast and short winter days. That depends on panel power excess.

-fab

terramir
Offline
Last seen: 5 years 9 months ago
Joined: Monday, July 21, 2008 - 18:09
Points: 33
Re: how to build a 12V input 24V (29V) output charger

hmmm I dunno but I saw a circuit that can boost with a few transistors one coil a 12V zener (although for my project I need to find one that does 29V) its a 6 to 12V 800 mAh circuit, but I figure I could adapt it if I can find the 29V zener use a little thicker wire for the coil and use a better Q3 which is the one the power passes through when the zener let's it be on. fairly standard boost circuit I just need to figure out what every component of the circuit does and hack into it :D. I think that sealed lead acid charging is fairly simple to work with. if I just knew if the controllers have the charge programming built in or it is in the charger bricks I'd be flying. My e-bike is almost finished I just need to figure out how to tense the chains (I built a tranny on my e-bike with a free wheel so I dun have to drag the motor along) it's just the chain tension I have a little problem with figure that could be fixed fairly soon.
My e-bike is probably the most ridiculous thing anyone has ever seen. but when it's done I can say good bye to busses and my car unless absolutly needed :D
terramir

abcd
Offline
Last seen: 15 years 7 months ago
Joined: Tuesday, June 19, 2007 - 19:15
Points: 16
Re: how to build a 12V input 24V (29V) output charger

I think SLA like current limited charger with voltage cutoff.

Since cost is major factor, why not just charge the SLA from 1 or 2 amp solar panel directly.

You could get a voltage cut out circuit to disconnect when SLA was at correct voltage level.

Buy more batteries and always have one set charging up.

terramir
Offline
Last seen: 5 years 9 months ago
Joined: Monday, July 21, 2008 - 18:09
Points: 33
Re: how to build a 12V input 24V (29V) output charger

well the catch with that is that my panels put out at max about 4 amps which would be ok but 17-18.9V and that voltage causes a runaway.
that's why a circuit with a constant current that raises the voltage would be better. and I would have to disconnect the batteries and put them in parallel instead of series.
terramir

fabelizer
Offline
Last seen: 15 years 6 months ago
Joined: Sunday, August 10, 2008 - 08:29
Points: 5
Re: how to build a 12V input 24V (29V) output charger

terramir,
Some say charging in parallel is actually better as the cells are more lilely to equalize with fewer in the series string to the source. I have not made up my mind on that yet, but it is logical that you are more likely to have a cell failure or imbalance in a string of 12 cells than in a string of 6 cells. (In my case I am using a 36V system, so 18 cells in series.) The "runaway" issue above is why you need a charge controller if the solar panel is not matched to the battery bank. Since you already have both the solar panels and the batteries, that is the direction you want to go in. Check out this site for some circuits you could work with, and build or modify yourself.
http://solorb.com/elect/solarcirc/index.html

-fab

terramir
Offline
Last seen: 5 years 9 months ago
Joined: Monday, July 21, 2008 - 18:09
Points: 33
Re: how to build a 12V input 24V (29V) output charger

well my solar panels are charging two 115Ah marine batteries the four batteries for my e-bike two 7.8 Ah/20 I already had and for the second bank I bought 2 7Ah cells (wanted more range than my 2 old 7.8 could give me.) would be charged off those batteries that's why I wanted to build that 12 to 24(28)V convertor.
terramir

Log in or register to post comments

Use code"Solar22" and enjoy 12% off for all solar Kits.


Who's online

There are currently 0 users online.

Who's new

  • Juli76
  • xovacharging
  • stuuno
  • marce002
  • Heiwarsot

Support V is for Voltage