Comment: Apparently, not all versions of the FT-817 are supplied with an Alkaline battery holder: Some versions (e.g. European) are reportedly supplied with a rechargeable battery pack.
For information about operating the FT-817 with Lithium-Ion cells, go here.
More conventional rechargeable batteries (such as NiCd and NiMH) have the rather unique property that they maintain a fairly constant voltage over their discharge cycle - around 1.2 volts - although they start out in the vicinity of 1.5 volts when "fresh out of the charger" and very quickly settle down to a lower voltage in the vicinity of 1.25 volt. They maintain their voltage fairly well (within 0.1 volts, more or less, depending on load and battery condition) until their charge is nearly depleted - and then the voltage suddenly nosedives.
This property makes them fairly easy to use. It would be safe
to use, say, 10 NiCd or NiMH cells to operate the FT-817: When freshly
charged, this battery would put out 16 volts (the maximum upper voltage
for the FT-817) or less, and quickly settle down to 11-12 volts - a
When I was originally putting this page together, it occurred to me that if you could cram, say, 2 more AA cells into the radio, you could probably get more usable lifetime out of them - maybe even run them down before the radio shut itself off! Because I already had the Li-Ion packs and the Radio Shack NiMH pack (see below) I didn't think about it much. Until recently.
Paul, AA1LL, recently read this page and dropped me an email mentioning the same thing - but he went a step further than I did: He ran some numbers. As it turns out, adding 2 more AA cells (and making it a ten cell pack instead of an 8) added significantly to being able to extract more useful life out of a set of cells. Paul's calculations are thus:
Assuming 9 volts = end of life:
9 volts = 8 x 1.125v = 8 x Vbatt after 1.3hr at
or, at 1 amp:
Using Duracell Ultra (one of the newer so-called "High Drain" types of cells with lower internal resistance:
1.125 v = v (2 hr, 0.5A)
1.125 v = v(0.5hr, 1.0A)
In reality, the '817 "dies" at about 7.5 volts or so.
The question comes up again, "Why would you want to use the '817 with Alkaline cells, anyway - especially if you wanted to use 10 of them, you'd need to put them in an external battery holder?"
Paul's answers are as good as any:
1. You can get them anywhere, probably
even in Afghanistan
One obvious advantage of Alkalines over NiCd or NiMH cells is that you could keep them in your "Emergency Radio Kit" for several years - and they'll still have most of their charge - whereas NiCd (and, especially) NiMH tend to suffer from self-discharge.
Another thing: After your '817 is "done" with them, they'll probably still run an LED flashlight for quite a while.
Has anyone actually done the "10 cell thing?" Paul is gearing up for trying it and we'll (hopefully) have some results before too long.
First off, if you get an '817, don't bother with putting alkaline cells in the supplied holder. You may ask "Why did they supply it with just an alkaline holder if it works so badly?" My response? A battery holder is very cheap - and people would complain if they didn't include something. Should they have increased the price of the radio by $50-$60 and included a NiCd or NiMH pack? 'Dunno... maybe... Anyway, after you have "run down" the alkaline batteries in your '817 there is going to be enough life left in them that they can probably be used in something that doesn't consume nearly as much current or care so much about the cell voltage - like a flashlight or your portable stereo.
We think of alkaline cells as operating at 1.5 volts per cell, but the reality is that this "nominal" voltage only occurs when the cell is brand new and unloaded. Typically, a type "AA" alkaline battery has approximately 2.8 amp-hours of capacity. What may not be so obvious is that this rating is based on a fairly low current consumption (something that the FT-817 only does when it is turned off...) and it is measured to a finish voltage of 0.9 volts per cell (90 percent discharge) - a voltage at which the FT-817 will not properly function. In other words, the usable capacity is much less that the cell's ratings would imply!
One possibility that offers better Alkaline performance are the newer types of "high capacity" cells. These have only (relatively) recently appeared on the market - and they are usually market especially for digital cameras and "high load devices." While the actual capacity of these cells may or may not be much higher than traditional cells, they do offer much lower internal resistance than their predecessors - a factor that may contribute to much longer usable life. Even with these types of cells, however, don't expect to be able to get very good operating lifetime from a set of these (rather expensive) cells.
"Why is alkaline battery life so poor in the FT-817?"
Many users of the FT-817 have complained that they get very poor life out of a set of AA alkaline cells installed in the FT-817. If you look at the nature of alkaline cells and the current consumption of the '817, you'll understand why:
The voltage across an alkaline cell drops as it is discharged: By the time it gets to 50% discharge, it is already down to about 1.2 volts. When it is 80% discharged, it is at 1.0 volts, and it is down to 0.9 volts when it is 90% discharged.
The nominal capacity of typical AA alkaline cells (down to 0.9 volts per cell - 90% discharge) is about 2.8 amp hours at room temperature (about 70 degrees F - approximately 21 degrees C) when subject to a rather low-current load (much lower than drawn by the '817, by the way.)
What is worse is that the internal resistance of an alkaline cell increases as it is discharged. When it is new, the resistance is in the area of 0.15 ohms per cell (1.2 ohms for 8 cells in series,) increasing to 0.3 ohms per cell when it is 50% discharged (2.4 ohms for an 8 cell pack) and up to 0.6 ohms per cell at the 80% discharge point (i.e. 4.8 ohms in an 8 cell pack.)
Translating this to actual receive use in the FT-817 is as follows (voltages are approximate and extrapolated from actual test data published by U.S. manufacturers - see the links near the bottom of the page) Note - this data is for "traditional" Alkaline cells and not the newer "high output" cells. (See elsewhere for a note on these newer cells.):
The upshot of all of this? Alkaline batteries really aren't very suitable for operating a "high drain" device like the "transmitting" FT-817. If you do use alkaline cells in the FT-817, do not expect it to work very well when transmitting on high power!
Finally, the battery holder and its connecting wires have a few tenths of an ohm resistance - further contributing to voltage drop and "apparent" reduced battery life.
(Note: These numbers are based solely on calculations based on data obtained from a battery manufacturer's web site for AA alkaline cells. Actual reports indicate that operational lifetime is worse than this. Let me know what your experience has been.)
Why can't I charge (those rechargeable) alkaline cells in the FT-817's battery holder?
First of all, the "rechargeable" alkaline cells do work as advertised - but they are not advertised to work well in "high drain" devices. The FT-817 is definitely a "high drain" device. If you insist on using them in the AA alkaline battery holder, their performance will be noticeably worse than that of "normal" alkaline cells due to their higher internal resistance (as compared to "traditional" alkaline cells.)
The FT-817 is designed to prevent "accidental" charging of Alkaline batteries in the supplied holder: To do so without very precise control and monitoring can result in cell rupture and possible damage to the equipment (or the operator!)
Note: Technical info (curves, charging, etc.) for the rechargeable alkaline types may be found at the Ray O Vac web site at the link near the bottom of the page.
One of the common 'mods is to cut the green wire: This will allow charging of the batteries in the holder - no matter what kind they are. But is this a good idea?
The answer is no - especially for any
types. Charging these types of cells (even when charging is
is best done under strictly controlled conditions. This involves
analyzing the cell's current state of charge, carefully monitoring the
cell's charge progress, and then terminating the charge (or changing
charge rate) in response to the way the cells charge is
This cannot be effectively done with series-wired cells without
the proper monitoring/control circuitry.
What about NiCd or NiMH rechargeable batteries in the battery holder, then?
Again, no. But, since I suspect that you will try anyway, I might as well explain why:
One of the main reasons why the supplied alkaline battery holder is a poor candidate for truly efficient rechargeable battery use is that the spring contacts have noticeable resistance of their own. When a few amps of transmit current are pulled, you are losing a few tenths of a volts due to resistance. This is simply wasted power, and as the contacts wear with use, this will only get worse. Finally, if the pack were shorted (and unfused) those springs may melt, and wiring and components within the FT-817 itself may be damaged - possibly making a mess and certainly causing a safety hazard.
Why is there this problem, then?
First, one should understand how a "normal" NiCd or NiMH pack is constructed: A good quality pack will have overcurrent protection and maybe even thermal protection as well. Why? NiCd/NiMH packs have a very low internal resistance when they are new and fully charged: A new, freshly charged AA NiCd cell can easily put out 30 amps (or more) when shorted - enough to melt tools or burn holes in shorting objects - including the cell itself!. If it happens to be the radio that is doing the shorting, then you can expect damage (i.e. burned components, wires, and circuit-board traces) from the current. In addition to the heat generated, a cell can rupture (i.e. explode) and cause damage to equipment and people.
Another "safety feature" of a battery pack often overlooked is the thickness of the insulation over the cells: Individual NiCd/NiMH cells generally have a single layer of rather thin "heat shrink" plastic over them. This insulation can be scraped off (especially if you have an '817 with sharp edges around its battery compartment) allowing the cell to short to the case of the radio. A battery pack, on the other hand, typically has rather thick insulation over the entire pack (in addition to the insulation over the cells themselves) preventing this sort of short...
How do you make it safe, then? I can't recommend that you actually use the supplied alkaline holder and modify it to allow use and charging of NiCd/NiMH cells - but I know that some of you will. Here are some recommendations as to how one can make it safer. You are responsible for any damage you may cause to you or your radio if you do this, however:
What is the best use for the supplied alkaline holder? Well,
connector is useful! Here's one suggestion. (Note:
that you know how to solder and that you have at least a
of common sense when it comes to electronics. You take full
for your actions and the results.):
Comments on an
external NiMH battery pack:
Just as adding one or two alkaline cells can greatly increase
operational lifetime by keeping the "end of charge" voltage up, the
same can be said for adding another cell or two to a NiMH battery
pack. Using the same cell size, this can't be done using an
internal battery pack so you must resort to an external one.
As is mentioned on the Optimizing
Consumption page, it is wasteful to operate the '817
at higher voltages than necessary for operation. While 8 cells
would seem to be ideal for this purpose, it is, in practicality, not
quite enough: During transmit, the internal resistance of the
cells plus that connectors and wiring can cause excess voltage drop,
causing the voltage to drop far enough below 8 volts to cause the radio
to shut down.
Having, say, a 9 cell battery pack can greatly reduce
this problem without too much increase in wasted energy - an
important factor if you are carrying this for portable use. Let's
take a comparison of the two situations on receive:
Notice: The information contained on this and related pages is believed to be accurate, but no guarantees are expressed or implied. The information on this and related pages should be considered to be "as-is" and the user is completely responsible for the way this information is used. If you have questions, additional information, or you find information that you believe to be incorrect, please report it via email.
For information about operating the FT-817 with Lithium-Ion cells, go here, and for information about operating the FT-817 with "other" types of cells, go here.
Another "battery" page:
The NiCd/NiMH page- This page describes in some detail the care and feeding of NiCd and NiMH cells and batteries. This explains how to keep NiCd cells going, and what that "memory" affect really is! (Hint: It's not the "memory" effect at all!) This page also has Links to manufacturers' information about various types of cells (NiCd, NiMH, Li-Ion, Alkaline, etc.)
Go to The
KA7OEI FT-817 "Front Page" - This is, well,
"front" page of the '817 pages here...
Any comments or questions? You can send an email.
This page maintained by Clint Turner, KA7OEI and was last updated on 20051026. (Copyright 2001-2005 by Clint Turner)