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Does anyone have any experience or advice regarding recharging an electric bike using a 12v to 240v power inverter

We are getting a campervan with a lithium ion battery (not sure what size) there is also a 100w solar panel on the roof.

Looking for ideas for recharging my wifes e-bike when we are off grid. I've looked on some bike forums but the advice is a bit confusing for an electrical simpleton like me

do you have a pure sine wave?

Did exactly this on our van last year, I used a 500w inverter from victron, it's wired straight to the 100ah leisure battery and then I have a socket in the garage connected to it, works perfectly well for my partners orbea which has ebikmotion battery. 

We had an inverter fitted in our van, hoping to charge ebike batteries. It works, but it draws quite a lot from the leisure battery. Our leisure battery is a more costly one - there seems to be 3 different levels. As I understood it at the time the dearer ones will cope better with high demand. Even so, even with the solar panel trickling power into the leisure battery, you could see the voltage of the leisure battery dropping. We found the best answer was to charge the bikes while driving as the van alternator could keep up with the battery draining. Being on a campsite with power hook-ups is another good way, so the leisure battery will be charging as fast as the inverter is draining it. 
We were advised to get a pure sine wave inverter (more expensive), though I don’t understand what that means. This was the advice of the very good auto electrician we have known for years and trust. He fitted the inverter for us.

Pure sine wave inverters are a lot kinder to electronics, so might protect your e-bike charging electronics.

Using an inverter is fine so long as it’s rated for more power than the bike’s battery charger.  As other said, you want a full sine wave inverter. 

As long as the capacity of your leisure battery is higher than your bike battery it should be fine for the battery as well given that you’re lithium not lead acid/AGM (which degrades on deep discharge).  Capacity is measured in Wh which is (voltage) x (Ah rating).  

A typical leisure battery is about 1200 Wh and an ebike perhaps 720 Wh so fully charging it will near drain your leisure battery.  100 W of solar probably isn’t enough (even in a sunnier country) to mean if you charge it then go for a full cycle that you’ll come back to a well charged leisure battery (7 hours to supply 700 Wh if fully sunny…) so I’d be thinking about a second solar panel…. 

Could you upgrade the leisure battery to a 200ah battery? It’s a straight swap if there is the physical space for it. Take a look at the van carefully and measure how big the space is. Then look on https://www.alpha-batteries.co.uk/ or similar and see if you can find a bigger capacity one which fits. That would give you a couple of bike charges, or one bike charge plus running the fridge for a few days.

Ideally you would just get a 12v DC to DC charger for your bike....  Seems insane to turn it into  230v AC just to drop back to DC 50v or whatever your battery is...

If you have an inverter already, then knock yourself out. 

A 100w solar panel will only deliver about 65w even on the sunniest day because they are only around 65% efficient, which is around 5A per hour, so a 100A battery would take about 20hrs to fully charge. Inverters aren't overly efficient and there are losses in the way they work which typically is around 10%. 

What about a cheap portable generator then you won’t drain your batteries ?

What about getting a spare battery for the bike? It seems that the inverter is only going to give you 1 charge before you have to either drive a long way (to charge the battery via the split charge relay from the engine), or wait a week for the solar panel to recharge the battery. Both aren’t very practical.

If you had a spare battery you can spend 2 days off grid riding, use the leisure battery for the fridge and other stuff, then move to a site with electric hookup to charge the bike batteries via the 240v circuit which your van will have when it’s on hookup.

You might even be able to afford 2 or 3 spare batteries for the price of buying and installation of the inverter.

I'm sure they'd be extremely popular running a generator for a few hours.

Thank you for all the replies, as ever it seems there is no one simple solution.

At the moment I think I'll hold off from lashing out a load of money, the bike will generally only be used for shortish journeys and a lot of the time we'll have a hook up so can recharge from a 240v socket

Don't know where you've got that from. Modern solar panels are ~20% efficient at converting solar to electricity but the stated power of the panels takes that into account. Decent solar panels bought from a reputable seller will generally give the stated power under optimal conditions or even more. I know I've got three on the garage roof and know of plenty others. You will get very wide variations on how much is generated due to cloud cover and the position of the sun during the day, and of course the annual cycle.

That sounds sensible, you'll get a feel for it and can upgrade later if you want. Generally, your 100W panel/battery/inverter combo will be good for charging devices, led lighting ect..... low power applications. But then you will find in the middle of summer on a cloudless day you'll have excess power and may be able to charge the bike. So when living off grid it will be a about preserving the charge in the leisure battery for your 'essentials', if you have any?

To be fair that's exactly what people used to do before solar became a viable option and the little suitcase style Honda models are really very quiet, not much worse than a diesel heater as full power.

Still not a great option though as you'd be running it for ages and it's a very inefficient way to do things. 

As mentioned above though, using 230 v ac (or a large diesel engine turning an alternator) to make 12v dc then inverting to make 230v ac to charge a bike at 12-36v dc doesn't seem like a particularly efficient. There has to be a better option.

Ditch the electric bike, use the battery to power the fridge. Fill the fridge with cream cakes, use the energy in the cream cakes to power a pedal bike.

Not really, the losses aren't that great compared to a DC-DC converter, often worth it for the cost saving of just having one piece of equipment which will work all your devices.

Put the rear wheel in a stand and pedal it backwards?

Eeking out the last bits of efficiency is usually more pain than up rating the system a bit.  A decent mains inverter is pretty efficient these days and has the bonus of working with all sorts of stuff.

No worse than screaming children tbh 

I’d prefer the genny to a moaning kid 

Fair enough. I guess it depends if you ever need 230v (we never did). 

If you literally just need a bike charged, then spending £30 on a 12v DC charger might be better overall value than getting a £300 pure sine inverter. But if you think you might find 230 AC useful, then the inverter is a better shout.

Seems like DC-DC can be around 95% efficient, and DC-AC and AC-DC the same, but two conversions so about 90% but it will, as ever, depend on the spec of the equipment you buy and the load factor etc.

I can't find ebike batter chargers running on 12V, and I would be really careful about what I plugged into one, decent ebike batteries are not cheap to replace. I'm confident I could put something together myself, but whether I would or not is another thing. Event the right connector for the battery can be hard/expensive to source.

A 300W inverter should be enough to charge a bike and they are about £60 for a decent one (there's always stuff on sale)

https://www.sunshinesolar.co.uk/Item/VPS300?gad_source=1&gclid=Cj0KCQjw...

Ah, the campervan doesn't come with an inverter right? In that case I would wait till you know the battery type and capacity, and what type of charge controller you have. Post that on here and we'll be able to advise accordingly.

err, isn't the right answer to get/borrow/hire a standard bike and thereby save yourself the headache of getting yet more gubbins to fit to your campervan. if your wife won't countenance that then perhaps hire at your detination and thereby you will get yourself a fully charged battery every day.

As I said I'm an electronics numpty

The van is an off the shelf from a big campervan builder so has controllers way beyond my understanding, it comes with a 105ah lithium ion leisure battery, it also has a 100w solar panel.

Some of the suggestions on here are talking about serious money that would buy a lot of nights with an hook up where I could just plug the charger into a socket.

I will pass on these suggestions to Mrs Dude along with the fridge full of cream cakes one

You may get some interesting replies 😉