Golden_HVAC wrote:
I have been buying 5,000 ma batteries for a couple of years from China, they are rated at 3.7 volts, and used in many flashlights. It is a 18650 battery, with 18 mm diameter, and 650 mm length. So 5 amp hours each. You can buy 3 gang battery holder, that would give you 11.1 volts total, so it will not work out well for a 12 volt system. 14.8 four batteries would be a little to high voltage.
The 5 AH 3.7 volt cells are running about $3 each when you buy them 10 at a time. Less if you buy 50 or 100 each. 48 of the cells, when wired 4 to a string, and 6 strings would give about 14 volts and 30 amp hours.
I was looking up this battery, the slightly larger diameter 26650 cell, 100 each for $411 with free shipping. This could give 25 strings of 7.2 AH each, or a fairly decent battery pack at 14.4 volts. Clicky Problem being it is 14.4 volts, not the nominal 12 volts used by motorhomes that is actually about 13.6 when charging and 12.8 when discharging. So it is a slightly higher charge voltage, and about 1.2 volts higher while discharging. I wonder how much of a difference this can make?
You can search the Aliexpress website for various batteries, and the holders to hold strings of 4 batteries, if you want to. They have some great prices. I bought a lot of LED light panels there as well.
Fred.
Go actually measure what you are getting out of that 18650, and you'll be surprised to find that you really only have 2300 to 2500 miAH in that 18650. Those are laptop computer batteries. The Chinese are notorious for padding the actual amp hours, you can go on Deal Extreme and read the comments to see what the batteries really put out, versus the BS printed or claimed on the label.
Fully charged, I end up with about 4.12V per cell. The voltage drops off pretty fast from 4.12 to 3.7V, where it sits steady for quite some time. Drop the voltage discharging much below 3.0V, and you just killed and destroyed a very expensive LiIon battery. Some of these batteries come with a built in "protection" circuit, but they are a little bit longer than the normal 18650... fine in a flashlight where there's a spring at the back to compensate for the additional length, but a whole other matter if you are building battery packs in existing holders. Also, these cells, often need individual compensation charges per battery, when it packs, to keep them all balanced in charge, and capacity.
