KX1 internal battery using NiZn cells

Hi all,

Nickel Zinc rechargeable batteries are not common, however HobbyKing sell them. I decided to get a batch and have a look at them in the KX1.

NiZn batteries are not for everyone. Firstly, the capacity is lower at 1500mAh than the typical NiMH battery at 2400mAh. The plus side is that the NiZN carry a higher voltage. It is at 1.85V at the top of the cycle and then slowly decreases throughout the cycle, but remaining well above NiMH, and even Alkaline batteries that start at just under 1.6V and decline to 1.1V over the cycle. NiMH spend most of their cycle flat at 1.2V.

For a radio like a FT-817 that linearly regulates the voltage, there is no point using AA cells with higher voltage, as the regulator literally burns the excess voltage as heat. The 1.2V of NiMH are fine in that application. The KX1 is a different matter.

The KX1 has a capacity for 6 internal AA cells. Using NiMH cells, these would deliver only about 7.2V for most of the cycle, which is below the recommended minimum voltage required by Elecraft. The rig still works – although I have not extensively tested it. The power levels generated are very low – perhaps only good for QRPp levels of 500mW or less. I am quite happy with QRP operating, but I don’t see a pressing need to go to QRPp at this stage.

The NiZn cells represent an opportunity to mix things up with a higher voltage that the KX1 can then use to generate more RF power. It won’t give me more operating time, but it will give me more punch. Here’s a look at 6 NiZn cells installed inside the KX1 AA battery holder:

Turnigy AA NiZn cells in the KX1 internal battery holder

The cells come charged, and showed 1.85V per cell and a total of 11.1V installed. I used the cells for several hours in the field, and I came back with the six cells developing 10.4V across them. The KX1 would develop low 1W to 2.5W depending on the band and (reasonable) antenna configuration. This was only a little down from what power it was developing with a 12.2V external supply.

The 1500mAh capacity would mean that these NiZn cells will deliver many hours, perhaps more than 20 hours, of operating time in the field. The low RX current draw of the KX1 is certainly a great factor here, especially compared to a all mode rig like the FT-817. This kind of setup would be really useful for multiday remote area activations, where the radio part of the gear needs to be kept to an absolute minimum for weight reasons – for example when South West Tasmania or Fiordland in New Zealand are part of the Summits on the Air program.

Regards, Wayne VK3WAM

Internal FT-817 NiMH battery option

Hi all,

A while ago I wrote about options for internal batteries in the FT-817. As detailed in that post, some are trying out LiPO options in the FT-817, and HobbyKing sell a 2600mAh 3S option. Provided operators watch the voltage level on the FT-817 screen to avoid excessive discharge, that would work well.

I still prefer keeping the LiPOs out of the radio – I am more than happy to use them as an external power source and often do. However, the internal battery is not great weight bank for gram. It has a 1400mAh labelled capacity. Mine would still be delivering the vast bulk of that even though I have extensively used it. It gives about 1 hour 20 minutes to 1 hour 30 minutes action when doing a SOTA activation with TXing at 5 watts. I have a BHI noise filter which is a little expensive on the juice, the 817 is drawing about 420mA on RX.

In my previous post, I highlighted that many NiMH batteries do not make the grade in the FT-817. They might get close to their labelled capacity (2100 to 2500mAh) typical on lower currents, but they struggle when 2A is called for. I did notice that the HobbyKing 2400mAh AA cells could handle a 2A load, so I was interested in trying them. That time had now arrived.

I used the 8 AA battery holder that comes with the FT-817 and loaded it up. This holder needs to be put in the radio either empty or with 4 or less cells as otherwise it jams. Care also needs to be taken that the cable does not get jammed as well. The holder can be subject to open circuit faults and I had a little bit of trouble with this.

HobbyKing AA cells in a FT–817

After sorting out those issues, I got on VK3REC, a local repeater, and proceeded to rag-chew at 5W FM. This would present the highest current load on the batteries. I was able to operate for nearly 3 hours before the batteries got to the end. Nice result, and the HobbyKing cells had no trouble throughout the discharge cycle.

Near the start, the 8 cells would present about 10.1V on RX and 9.1V on 5W FM TX on a multimeter. The FT-817 display would show 9.6V and 8.4V at this time. The 8.4V on TX remained at that level for about 90% of the discharge cycle. The final part of the discharge cycle was more graceful than the internal battery, with the RX voltage slowly drifting down from 9.2V FT-817 display to 8.8V. The multimeter was about 0.2V above each of these levels. The 5W TX was at 7.8V when I stopped the cycle. The FT-817 will power off if it drops below 7.5V.

On the whole, I am very happy with the AA cell’s performance and can recommend it for use with the FT-817. I would suggest charging the cells individually in a NiMH smart charger. Alternatively, two lots of 6 hour charges in the FT-817 should fully charge the 8 cells from flat. The green cable in the battery pack needs to be disconnected for the FT-817 to charge the pack.

73, Regards, Wayne VK3WAM

Upgrading a camping lantern

Hi all,

My family goes car based camping a few times a year. I also go pack carry camping as well, but that requires a different set of gear. A number of years ago I purchased a 7W fluorescent camping lantern. It has worked well, but now the battery is cooked. Here’s a look at the box of the product.

Designed to fail

The cheaper – and not so cheap – lanterns can often have a poor design that can lead to early failure because they do not treat the internal battery appropriately. These units are often supplied with an internal sealed lead acid battery (SLA). My one had a 4Ah 6V battery. This can power the lamp for about 3 1/2 hours. One problem is that SLA batteries should not be cycled more than 50%. They also should be stored fully charged. The 50% cycle means that this lantern should have only been used for 1 3/4 hours on a full charge, and then it needs recharging. No mention of that in the small manual that came with the lantern.

The second problem is that the charging circuit built into the device does not charge the Pb battery in a way that is according to spec. The charging voltage is too high. It’s going to cook the battery a little bit on each charge.

So now I have a lantern that does not work. Should I just throw it away?

Solution

The rest of the lantern seemed ok, it just didn’t have a working battery. I could have just bought a new battery from the supplier, but they charge more than the cost of a new lantern. So, I thought I would replace the battery with something that was more suitable.

Firstly, I have been using LiPo packs in Amateur Radio applications – powering a low and a moderate power radio. A 3S – 3 cells in series pack has a voltage of 10 to 12.6V. Too high for this lantern directly, but it could be converted to 6V. I found some LiPos at Hobbyking that would do the trick.

Three of these fit into the battery area of the lantern quite snugly. I cut the main cable to a short run and used JST-XH connectors, which are shown in the picture above, as these connectors are the same on my other LiPo’s – makes it easy to charge on the chargers that I already have.

Having three of these inside, with 6VDC regulation, gives me capacity over 3 times the old battery, but I can use nearly the whole cycle, so it is really 6 times the capacity.

I grabbed a DC converter off Ebay that outputs 6V up to 3A. The lamp draws about 1.2A, so that is easy going for this converter.

I would not be using the existing charging circuit. It was no good for the Pb battery, and it certainly would be no good for these LiPo packs. I could make use of the LED in the lantern that indicates when the lantern is charging. Instead, I would use this LED to indicate that the voltage in the LiPos was good. The 6V converter would work with an input voltage of 7V, which would mean the LiPo packs driven down to an average of 2.3V per cell – far too low. Instead, I would use this LED to indicate when the packs were getting flat, at around 11V or just a little under. The LED would be on when the battery was ok, and go off when not.

I needed a simple circuit to drive the LED. From the LiPo voltage source, I fed a 470ohm resistor and then three Zeners. I selected three, because the breakdown voltage of around 11V was what I needed, and I had these on hand. Three of these zener diodes, each with a breakdown voltage of 3.6V, in series gave me what I needed. The current on the zeners would be about 3mA – set by selecting the 470 ohm resistor. Connected between the Zeners and the resistor is the base of a 2n4401 transistor, with the LiPo voltage on it’s collector. From the emitter of the transistor, I had a 1K resistor. This would have typically about 9V across it, meaning a current of about 9mA. This was in series with the LED, which has it’s own 2V drop. So from the LiPo voltage, the transistor would have a drop of around 2V when the LiPo pack was fully charged, falling to zero when flat, plus just under 9V for the resistor and 2V for the LED.

This circuit was put onto some veriboard and put into the lantern’s battery compartment. It is shown below and the DC converter is immediately beside it. Below is the factory built charging circuit that is now unused.

Unfortunately, I mixed up one of the JST-XH connectors on one of the LiPo packs, with the plastic housing having wrong polarity. I made one of the associated connectors to match it, and marked them both with tape so I don’t use it for the other packs. I’ll just have to live with it.

After all of that, it was time to turn it on. Works well – very pleased with the outcome. Now, I can safely use the lantern for about 11 to 12 hours between charges, rather than under 2 hours. This has turned into an upgrade rather than a repair of the lantern.

Regards,
Wayne Merry