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« on: November 02, 2024, 03:30:39 AM »
Has anyone tried to make a simple solar panel based charger for a Zero that uses the Anderson port? I have a 2020 Zero FX 7.2 and would like to have an off grid charging system for my bike at trailer I use in the summer. I would much prefer not to have an inverter based and/or battery buffer based solution to keep the solution as inexpensive as practically possible and not have to worry about unattended storage of buffer batteries in the winter where temperatures could dip down to -30C on occasion. The FX would only be there in the summer.
I believe a Zero battery pack is deemed full when the pack voltage reads 116.4v and is deemed empty at about 95v. I note the simultaneous use of two external Quiq chargers and the internal charger with the FX is officially sanctioned by ZERO. I believe the three chargers collectively consume about 2.8kw, and provide about 2.2kw on the DC side. A charger powered by a maximum of 2.2kw of solar panels is what I envision.
The simplest arrangement would to have solar panels in series where the maximum outputted voltage is at least 116.4v and stays below some maximum. In version one of this charger I would be quite happy to monitor the display on my motorcycle and safely shut down the charger when the bikes battery state of charge display hits some percentage value, like 99% or 100%, or when the green charging status light changes from flashing green to solid green. I note the charging countdown timer gives a rough estimate of when the bike will be charged so I would be by the bike when it is close to fully charged.
Let's call the maximum voltage that should be allowed on the Anderson port during live charging VMax. What is VMax ? Can we make a reasoned guess ? Can we have a safe charging strategy even if we don't know what VMax is ? Has anyone bothered to measure VMax ? Can they tell us what it is and how they measured it ? Since this charger is basically a series of solar panels, we need to have an idea of the amount of voltage our ideal series of solar panels put out.
The voltage a solar panel puts out varies with the amount of solar radiation collected, the ambient temperature and probably the age of the solar panel. Used solar panels a few years old and in good condition are quite inexpensive. That is what I will use. Of course I'll test them before using them. Solar panels are rated. The ratings taken under standard test conditions include Maximum wattage output(Pmax), Open circuit voltage(Voc), and voltage(Vmp). My limited experience charging nominal 12v car and motorcycle batteries suggests considerations.
An AGM or "glass mat" 12v battery is at 100% charge when it measures 12.8v with no load. An "old school" 12v auto battery is fully charged at 12.6v. Having said that, to get the true voltage of a car battery one must let it settle with no load, maybe sit "overnight" after it is charged to measure it. A nominal 12v solar panel can measure around 20v in an open circuit. When a low "12v" battery reads 12.0v and is connected to a 5watt 12v. solar panel, the voltage across the terminals is a bit over 12.0v. Similarly if you start your I.C.E. motorcycle or car up and then measure the voltage across the battery terminals you should get a reading of around 14v. The vehicles shop manual should give a range of voltages that indicate the cars charging system is working properly. When I use a nominal 12v charger on my motorcycle or car and measure the voltage across the terminals I see a slow rise in voltage to about 14v until the solid green light of the charger deems the battery is charged. At least with lead acid batteries we can conclude that chargers apply a voltage higher than the batteries "fully charged" voltage.
So what can we infer here? Please electrical engineers chime in , or people technically familiar with Zeroes battery packs, please chime in.
I venture to hypothesize that the combined voltage Vmp should be somewhat higher than 116.4v. Let's call that CVmp. I expect the voltage measured across the live circuit should drop to somewhere between the current pack voltage and CVmp and then rise as the pack gets charged. I optimistically hope that the display on the motorcycle will let me know when the bike is close to be fully charged and thus when I should safely disconnect the motorcycle from the solar panels.
Should I try this out? Should CVmp be 116.4v ? 120v ? (Both probably not) 140v ? 160v ? For instance if I put four 250W solar panels in series that are identical and made to have at least 4 in series and have a Vmp of 35v each, would that work well?
One consideration is if the voltage across the circuit temporarily drops. Say a cloud gets in the way. When I use only my Quiq charger to charge, I connect all the wiring, then turn on the Quiq charger, then key on the bike. After the bike starts charging I key off the bike. When I then turn off the charger, after a second or so a relay on the bike breaks the connection. I don't want a cloud to break the connection. The obvious reason is the charging process will have to be started over again but more importantly, from a safety point of view, having a Kw or so of power with no load sounds like disaster. At least that is my instinct. Would a high power capacitor in the circuit prevent this from happening, or does that just mean the connection gets broken after a few seconds of low solar panel output and that this design will inherently not work. Or maybe this is not a consideration at all as light clouds might not lower the output power enough to cause the bike to trip the relay. Or maybe I should just leave the bike keyed on until I am ready to stop the charging process.
There are other considerations. What EXACTLY should I do to prevent lightning issues. Nothing will be connected to the panels when it's overcast. They will be attached to a steel roof. I don't even know if the roof is grounded.
Any helpful thoughts ?
