PRC-174 BATTERY PACKS
This new page contains info on several types of do-it-yourself battery packs you can make for the PRC-174 HF packset.
To date, I have made and tested the following battery pack designs:
21 D-cell NiMh 9000mah 25.2V
21 D-cell Alkaline 25.2V (not rechargable)
63 AA-Cell NiMh 6000mah 25.2V
16 18650-Cell Lion 8000mah 26.4V
Why the extra cell? You may have noted that I usually add an extra cell to my NiMh packs, making them 25.2 volt packs. Although this really doesn't extend the capacity of the battery pack, it does operate the pack at a slightly higher voltage which keeps the LED battery indicator on the PRC-174 in the five-LED range longer, and the PRC-174 can easily tolerate the extra voltage. If you build a 24 volt pack, you will operate at four or three LEDs during transmit most of the time.
For long-term storage without having to worry about self-discharge, you can make a disposable pack out of ordinary D-cell flashlight batteries. When you catch them on sale and buy in quantity, the price isn't too bad to have one of these kicking around. It will last for years.
A note on overseas eBay cells. Many of the cell specs on battery cells on eBay are mis-stated (that's putting it nicely). I suggest buying a few cells and testing them before committing to any one supplier. I have had very good luck with the blue Tenergy cells. Also, DuraCell US made NiMh cells are available at a good price, and they are true to their specifications.
A good source of lithium ion cells is from used laptop battery packs. Also there are a few sellers on eBay who test and re-certify used 18650 cells which sell for a couple dollars a cell. The 18650 cell is 2000mah so two in parallel give you a 4000mah pack which is usable on the PRC-174 and a lot lighter than the NiMh packs. I make these with 8 pairs of cells in series, arranged in two L-shaped sticks (see photos).
The Triton2 charger will not charge more than 5 L-ion cells in series. This problem is overcome by wiring the pack so it is two sticks of 4 cells in series, wired out to a four pin molex power connector. Then you make two cables for the opposite end of the power connector. One cable is for charging, and wires the two sub-packs in parallel where it is charged on the Triton2 as one 4-cell L-ion pack at 8000mha. The second cable wires the packs in series, and is for use powering the PRC-174.
The lithium-ion pack requires special handling when charging. When L-ion cells are used in a laptop battery pack, they are generally used with a "smart" charger board that monitors the voltage of each cell, and can perform cell balancing as part of the charge sequence. This is beyond the scope of our DIY battery pack, so you must be careful when charging these packs! I use a Triton2 charger which can perform two of the three required stages to charge these batteries. (It can't balance the cells connected in series.)
If you do charge these yourself with a power supply, you must remain present during the entire charging process, and you must limit the current and voltage to safe limits. Read this Wikipedia link and scroll down to the charging procedure and be sure to read the safety section. Limit the voltage to 4.2V per cell, and limit the current to 20% or less of the cell current capacity. Monitor EACH cell voltage periodically in case one shorts which will result in dangerous voltages applied to the other cells!
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