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 Topic: Charging Ebike Batteries while off grid
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27/1/2021 at 2:14pm
Location: Hampshire
Outfit: Hymer Nova S
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I would suggest here a little caution and research is required before venturing down the direct DC to DC route, on two obvious counts.
1) As these are branded bikes, there could very well be a handshake protocol between the charger and battery management system to authorise a charge. Our E-bike is made by the same company holding the Raleigh brand, and has such a handshake.
Looking if the charger's output plug has more than two pins will give strong hints of that here; it can be not a case of simply putting a DC voltage into the battery.
2) Lithium batteries can be hypersensitive to the charging voltage, between undercharging and wrecking.
I note the charger accepts 100 VAC with a peak current of 1.8 Amps, and its output is 42 VDC at 2 Amps.
From this we can conclude it employs some sort of "chopper" technology, and that its maximum continuous rating is not greater than 180 Watts.
The nature of these devices can make them sensitive to the "quality" of the AC waveform, so I would not "try" powering it with any old inverter, but one very specifically sold as a "Pure sine wave" device. The charger's continuous drain of 180 Watts, suggest to me a quality inverter of around 250 to 300 Watts is the optimum size if buying for this task.
My e-bike's maker states it should not be charged via an inverter. I suspect because many users would not buy an inverter of adequate waveform quality? At £145 for a replacement charger, I have not tried, even with our pure sine wave inverter.
The practicality of off grid recharging e bikes is also affected by the significant capacity e bike batteries hold. Ours is just over 600Wh. Our caravan's battery is 90 Ah, so its practical, usable Wattage hour is 50% of 90 x 12 = 540 Wh. So to fully recharge the bike requires more than I sensible have available. Therefore, one needs to think in charging a little and often, in this off grid situation.
Considering a 100 W solar panel, the first observation is it can't keep up with the load powering the charger, we know about 180 W, so a battery will be being drained to make up the shortfall
The 100 W solar panel during the summer, probably can average a yield of one third its rating for 8 hours a day. Some days it will be better some not, but IMO that's a reasonable working basis. Therefore, budget a 100 Watt panel giving, 100 x 8/3 = 267Wh.
Therefore the battery will be drained, in my case 600Wh-276Wh = 330 Wh, or in battery terms by 28 Ah. A tolerable drain on a 90 Ah battery assuming few other drain demands are made of it.
However, IMO it points to a 100 W panel system with its battery is by far better used frequently to "top up" our e bike. I suggest an early morning recharge, allowing the solar controller to gather the best it can of the rest of the day's yield.
In real life, despite thinking a lot on this, pre buying the bike in 2016, we have found our 100 mile range, with very occasionally grabbing a quick lunch break recharge at a pub. tea house when really needed, we have had 5 to 7 day breaks with all the cycling we "need", without trying to recharge off grid.
Post last edited on 27/01/2021 14:31:58
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via mobile 25/1/2021 at 4:26pm
