Portable Power Manpack & off-grid power strategies

Hello Operators.

Recently I posted a video entitled “Portable Power Manpack for Civilian Off-Grid Communications”. It’s a video overview of a man-portable shoulder sling solar generator, useful for a variety of use cases.

The system is scalable, can be constructed with a variety of different components, and follows a Lego block philosophy.

One of the questions coming in often in the video comments was “How can the two charge controllers know what state of charge the battery is in, and sync with one another?”. This is an easy one to answer. Lithium battery chemistry uses a “constant current constant voltage” charge profile (CC/CV). There is no float, absorption, bulk,.. as we find with lead acid batteries. With lithium batteries, either it’s charging or it’s not. This on or off State is directly related to the battery voltage. So the dual charge controllers in this build are are in sync because of the battery voltage. When the battery is full, both charge controllers will show full even though there’s no physical connection between them. When the battery is at less than full, each charge controller will work to charge the battery until it is full. Get it? It is either charging, or it is not!

Component list:

Solar panels used in the video:

Off-Grid Power Strategy

Rather than rambling on about the next part of this post, a “food for thought” picture post, is worth a thousand words.

The point of the above image has been a thorn in my side for quite a few years. It is simply too difficult to get the emergency communications community, preparedness community, or general radio operators to understand this point. There’s no spite or anything, people simply don’t take the off-grid power aspect of communications seriously. If anything, it’s an afterthought!

Far too often we incorrectly assume those old car batteries we have out in the garage, will be a perfect fit for our grid down power needs. That may be a great hack in a pinch, but it’s definitely not a long-term strategy. For emergency communications and preparedness, we need a purpose built, reliable power source specifically for our communications gear. That old battery out in the garage is there for a reason (it sucks). Leave it there as a stop gap, while you plan and build your off-grid/grid-down power strategy over time.

Our strategies for power should include:

  • Reliable battery storage 24-72h
  • A mechanism for charging the battery storage. Solar, wind, hand crank, …
  • Power distribution & spare fuses.
  • A mechanism for moving the battery and charging system to the place it’s most useful.

Connecting the dots

It isn’t always possible to lead you straight to the point of each and every video. It is nice to believe Operators watching my channel or reading my blog, will watch or read enough of the videos and blogs, to get the “Big Picture” on their own. Just because I don’t drop the “buzzwords/tags”, eg zombie, 2A, disaster, civil war, … doesn’t mean the video is not relevant to the viewers goals. Remember, I am not selling anything. I just want to share good information. There is no “profit” model, so pay attention 🙂
The following playlist is the “How to solar power your portable ham radio” series. There is lots of good information there, even if the buzzwords are omitted.

My own off-grid power strategy

  • Home station
    Currently, the home station has 7x 100 watt Renogy solar panels (1x is a spare). These are wired in 200 watt sets, each feeding 1 of 3 Genasun GV-10L 4S LiFePO4 MPPT charge controllers. The charge controllers are connected to the 576 watt hour solar generator we built on the channel some years ago. You can watch that video here: https://youtu.be/Nf9X4YIK9xA Each 200 watt set gets its own Genasun GV-10L MPPT charge controller. Usually, one to two panels are added each month. The goal is to keep going until we have 3kw of solar (not all for comms). 1kw for communications, 2kw for household use.
  • Portable station
    The portable station is always evolving. Here is the current setup for 3 different scenarios.
    Casual man-portable ham radio: Using any number of QRP rigs, the basic power supply is a 2.5ah LiFePO4 based portable solar generator we built on the channel in autumn of 2022. I generally use a 60-watt PowerFilm panel to power the 2.5ah LiFePO4 pack. If there is going to be an overnight trip, I’ll use the 5ah version we built a couple of years back. These low capacity power supplies are made possible by our “low current strategy” You can watch the latest 2.5ah solar generator video here: https://youtu.be/HgQ3m6rzJko
    Multi-Operator Field station: The field station has lots of different portable power options, from the builds on the channel. Currently, the 24ah portable power manpack is the go-to power supply for medium duration trips with multiple operators. If the stations are “high amperage”, I’ll usually use one of my DIY builds with up to 60 amps output, rather than a store bought battery. Solar panels are almost always PowerFilm panels because of their size and weight. I’ll choose between 2x F16-7200 120 watt folding, or 2x F16-6000 100 watt folding.
    – For a Grid Down emergency where temporary power for a repeater, digipeater or RMS gateway is required, I’ll deploy either than 575wh solar generator or the 307wh solar generator mentioned above. The choice really depends on the time of year. Solar panels are almost always PowerFilm panels because of their size and weight. I’ll choose between 2x F16-7200 120 watt folding, or up to 4x F16-6000 100 watt folding, running into parallel charge controllers.
    It is nice being the “power guy”, but if it fails, you’ll never hear the end of it.

As a niche topic, this blog and YouTube channel will never be very popular. Regardless, the blog and channel will always be upfront and honest about off-grid comms, off-grid power, and communications for emergencies, disasters, personal preparedness & defence. Please keep that in mind when wondering how that video or blog fits in.

Lots of effort goes into these posts. Researching each component, software application, strategy, pragmatic field testing. When you see these posts, the mistakes and blunders have already been filtered out. If you find any value in that, share this post and/or buy me a rootbeer.

Julian oh8stn
YouTube http://www.youtube.com/@oh8stn
Buy me a rootbeer: https://paypal.me/oh8stn/2usd

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