Instruction manuals

Re: Instruction manuals

Welcome to the forum Woz,

I think we need a little bit more information. Are you looking to make a small solar system that will supply 12 VDC or 120 VAC to power off the shelf battery chargers, or are you looking to build your own battery chargers?

PNjunction is worried about your use of 18650 cells (I think). Many people by unprotected 18650 cells for use in flashlights because they are a bit smaller than protected cells and will fit in the same space a pair of CR123A cells. But using unprotected cells is on the risky side. Without the battery management/protection, it is very easy to over discharge the cells and have them catch fire on recharging. Candle Power Forums is a great place to learn and even purchase components/kits for flashlights and charging setups (from posters that cell through their posts on the forum).

Regarding solar, there are two major ways to do it... One is a solar panel direct to a battery charger. Lightest, smallest, and potentially the cheapest way to go. However, most battery chargers for fast charging NiMH and Lithium Ion cells have a microprocessor that keeps track of the charging process and need stable input power/voltage to make sure that the cells are not damaged during charging (Charging at ~C/2 or faster rates--Charging in 2 hours or less). Using a solar panel directly is difficult because the charger can collapse the solar panel voltage if the panel is not large enough and the sun bright enough to supply the needed power.

Another way of charging is around a C/10 charge rate--Many chargers will not even have any termination logic as cells will not over heat at C/10 and NiMH can take that rate of charge even when full without damaging the cell too much (if cell is removed from charging within a few days). And a simple voltage regulator should be OK for LI type cells (depending on chemistry--But I am not sure here--Been a long time since I looked and their charging requirements--And you need to be sure you do it correctly. Many LI constructions/chemistry do not like over charging at all either). Using a C/10 charge rate (10 hours) will mean that it can take 2-3 days to recharge the batteries from "dead" (2-4-6 "hours of sun" per day depending on seasons/weather/shading/etc.).

The other way of making a solar power system is to use a solar panels+charge controller+Lead Acid (or similar) battery. The solar panel and battery are put out in the sun to recharge the battery bank. And then you use the stable 12v/120v power to plug in battery chargers to fast charge your flashlight batteries. This has the advantage that you can recharge your batteries when needed (day or night) with fast chargers (which need stable input power). The disadvantage is the weight/size of the extra battery and the 10-20% or so of "extra losses" with the buffer battery.

Solar panels are highly variable in output voltage (from zero to ~17.5 volts Vmp for "12 volt" panels to >22 volts Voc for cold panels) (Vmp=Voltage maximum power, Voc=Voltage open circuit). And 12 volt batteries will output from 10.5v to >15 volts (dead to recharging/equalization). And those wide voltage ranges are a pain to design/find fast battery chargers to operate on that range (cars run around 12-14.2 volts and some automotive plug type chargers/devices have been known to die when subjected to >~14.5 volt volts that is used to recharge deep cycle flooded cell batteries).

Anyway--Can you tell us a bit more what you are looking for?

-Bill

Re: Instruction manuals

I'm not sure if Candle power will have charger kits (been a few years since I used to hang out there).... But they should be able to help.

A big issue with solar power is the variable output current/voltage.

If having a buffer battery to store power during the day (12 volts/120 VAC inverter/etc.), then powering what ever charge controller/chip set you want will be a lot easier--Especially if you want fast charge.

If you want C/10 rates of charge, then you can setup/build a simple current limited (analog), voltage/timer cutoff, or switch mode current based power supply with some sort of feedback control (monitor time/voltage/current/temperature of cell).

Then it gets back to the amount amount of power you want to controller. Solar panels are current mode sources--So if you can pick a current limit and find a panel that will meet that (and design something to stop charging when full/voltage limit reached). Or you can use a buck mode switching power supply to down convert voltage efficiently (Vin*Iin~Vout*Iout) to that used by the battery. You could setup the power supply to voltage control or current control... All depends on your goals and what you have available (size of solar panel, battery in the middle, light weight, fast charging, cheap, rugged/reliable).

The more power/higher the current you wish to supply, the more complex (probably) your system will become.

The 12 volt battery as an intermediate storage element will give you a nice portable power system--As well as a good base for charging rechargeable. If you want high tech (high power, low weight), you could look at a 12 volt LiFEPO4 battery for the buffer (not cheap, but very interesting capabilities).

If you pick a standard voltage/chemistry for the buffer battery, then a MPPT type solar charge controller is pretty readily available (not cheap).

One of the posters here "Sun Dog" asked me a while ago about this solar charger on a chip:

http://www.ti.com/product/BQ24650
http://www.ti.com/tool/bq24650evm-639

It is a pseudo MPPT charge controller on a chip with an output voltage range that may cover what you are looking for (from a quick read, you program the solar panel Vmp and it does not adjust for changing solar panel conditions)--But it may do what you are looking for.

-Bill