Hi,
I have two Raleigh Stow E bikes which I would like to use when off grid.
The problem I have is charging the batteries while off grid, my caravan as a 100W solar panel fitted on the roof and I have two 110A/H lead acid leisure batteries. The details of the chargers for each bike is Trans X Input 100-240V AC, 1.8A(max), Output 42.0V DC, 2.0A.
The options I have considered so far are,
A. Put an additional 100w Solar panel on the roof of the caravan and use a 500w inverter to supply the charger.
B. Buy a folding 100w Solar Panel use it to supply the spare battery and use a 500w inverter to supply the charger, also this Solar Panel could be used to supply the caravan battery when not used for charging the bike batteries.
I have also heard about DC TO DC chargers which are apparently more efficient but unfortunately I have no knowledge of these, neither can i find any information on them.
I would avoid converting the DC to AC then back to DC to charge as that wastes a lot of power to run. You are losing in a min of 20% of your energy doing this. For example we have a network/router that has a battery backup from a small battery supply if we lose mains power - If i connect the devices via a 12v charger I get a couple of hours useage off the battery. If I plug in via a 230v inverter I get about 40 mins if I am lucky!
You need a 12v charger then you need a supply for this via more solar and battery storage.
Also look at some of the new portable power banks (also known as camping generators in the US) that are starting to go down in price. You can connect these to the caravan to charge off the solar and work with the caravan battery. But bear in mind they arent cheap - a 300w pack is going to set you back £300!
First thing is to get more solar solar as you can afford. Then look at how to store what they create to be able to run your chargers.
the snag is finding DC to DC chargers is difficult..
i take a couple of small scooter types e bikes away with me and a couple of laptops.. they all take mains chargers.. its just a lot easier (and cheaper) to use a small inverter and make up the losses elsewhere..
Thanks everyone for your replies, someone on another site told me about a 12volt to 36-42 volt charger see website below might give them a ring as well as increasing my solar panels.http://www.powatechnic. com
I would look at using the 12v DC charger from the car alternator when you can and only using the caravan batteries for bike charging when needed. Also keep an eye on your weights with extra battery, panels etc.
------------- 'A sure cure for sea-sickness is to sit under a tree'
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.
all this is being over complicated.. off grid is easy.. all it takes is an adequate battery or batteries and an adequate means of charging these batteries..
the average caravans 12 volt system is not designed for off grid use and isnt up to the job..
i have just made my own caravan off grid capable and have pretty much explained how i did it and how much it cost me..
it is quite easy to do but it does cost money.. my advice is that if off grid is your thing and you want 12 power be prepared to do what you have to do and spent what you have to spend.. else forget about off grid as most people do..
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Topic: Charging Ebike Batteries while off grid
via mobile 25/1/2021 at 4:26pm
