Solar Power And Ten Tec’s Awesome Closet Kilowatt
Solar Power for the Ten Tec “Closet Kilowatt”
Solid State DX Wonder of the 90’s
Over the last year and a half, I’ve been restoring a Ten Tec “Closet Kilowatt” from the late 80’s. The brochure excerpt shows a model 253 Automatic Antenna Coupler, a model 420 Hercules II amp and a model 562 Omni V. My updated version substitutes the model 564 Omni VI+ from the late 90’s.
I’ve been teaching it how to work on some of the digital modes like FT-8. To that end, I repaired the Omni VI Plus, built cables to make it talk to a Mac and the other Ten Tec devices, and added other accessories to facilitate the digital modes. All of that is working, but I never really discussed how I am powering the whole thing. Especially the Hercules II 550-watt amplifier.
Previous posts in the series
- How To Fix A Great Ten Tec Omni VI+ Tranceiver
- How To Add CAT Control To A Ten Tec Omni VI+
- How to FT8 With A Ten Tec Omni VI+ With A Mac
How to power a 550-watt solid state amp
Originally, the Hercules II amplifier came with a large and heavy 12-volt at 80-amp power supply. I found several amps for sale, but none of them had the power supply. I looked into modern switching power supplies, but was reluctant to invite another noise source into the shack. That left either waiting for an original or other large analog power supply, or powering the whole thing with a giant battery.
Solar is the answer
Another goal for my shack was to power it using solar energy. Apart from the challenge of seeing how far I could get with solar, it had obvious advantages for disaster preparedness. I gained considerable experience powering our water supply and providing emergency power to the house using solar. And, I already had a small solar power system for the shack. Powering the Hercules II amp would be a good challenge.
You’ll need a good battery
I recently acquired a cache of lithium iron phosphate (LiFePo4) cells and even built a small 12-volt battery using four of them. Since the amp required 12-volt power at 60-80 amps,and I had hundreds of these 60 amp hour cells, it looked like a solution.
I thought about trying the 4-cell solar generator I had just completed, but these cells prefer discharge rates of no more than 30 amps. What about doubling the size of that battery? Four sets of two paralleled cells and then connected in series. That would make a 120-amp hour storage capacity with a comfortable discharge capability of between 60 and 80 amps. Perfect.
Use what you know
Since I had experience from building the solar generator, I could reuse most of its basic design. The biggest difference would be eight cells instead of four. They would be connected in series-parallel to equal 12-volts (sometimes referred to as a 4-series, 2-parallel configuration).
Building the battery
I won’t repeat the details of constructing the solar generator, so you might want to review the article posted on our sister blog, Roy Creek Ranch. It will help you understand what follows.
Pretty simple
The new battery is actually simpler than the solar generator since we won’t need Anderson Power Pole connectors, voltage monitoring or an inverter. Just two cables are needed: one rated at 80 amps or more to the Hercules II amp, and a 40-amp connection to the station 12-volt system. Both will connect to the battery using ring terminals on the insulated power posts.
Solar upgrades to the shack
As shown in a post describing the original solar power installation, a pair of 150-watt panels connect to a charge controller. It is then connected to the main 12-volt station battery. That is what we’re upgrading with the 120-amp hour LiFePo4 battery.
Both are now a 24-volt system, minimizing power loss over the 100-foot distance from the panels. The new charge controller is a Maximum Power Point Transfer (MPPT) type, making it more efficient as well. In short, much more of the 300 peak watts the panels can generate makes it to the battery system.
Mechanical details
The other differences with the new battery are mainly mechanical. There is still plenty of room in the milk crate for the battery. The cells are strapped together with Kapton tape.
The BMS is attached to one side of the assembled cells using double-sided tape. The breaker/disconnect is mounted to the interior of the milk crate as are the insulated battery posts. The rest is simply wiring with appropriate crimp-on ring connectors.
The other difference with the Solar Generator is adding a sturdy top to prevent metal objects from contacting the battery terminals and bus bars.
It is made of 1/8-inch black HPTE plastic sheet, cut to fit the milk crate opening. It is attached by four aluminum angle brackets and sheet metal screws. The wiring to the Hercules II amp and station 12-volt system simply comes through two of the many holes in the side of the milk crate.
One final detail. Since the battery assembly is quite a bit smaller than the milk crate interior space, I needed something to keep it from sliding around. Foam packing material was handy and seemed to fit the bill.
Performance
The battery has been in service for over a year now with no problems. The same bluetooth-connected iPhone app is used for monitoring as described for the Solar Generator. I’ve done a lot of FT8 and CW at 50 to 100-watt power levels with no problem. I use the Hercules II amp more intermittently, mainly when trying to break through an SSB pileup. The system generates full power with the amp on (up to 80 amps) with no problem.
The battery powers nearly everything in the shack — several radios, accessories and lighting — with the exception of the Mac. I’ve kept records since the battery went into service and it has rarely been below a 70% state of charge. A sunny day is more than enough to charge it back up. Of course, a string of cloudy days can be a problem, but then I just plug the Victron Smart Battery Charger into the station 12-volt power system to recover. Here in our sunny Central Texas location, that doesn’t happen too often.
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