[Closed] Do we have any electronics bods on here?

Amps multiplied by volts will give you the number of watts produced. I'd add on a margin of at least 25% to the size of your inverter. 500 W would be my choice as a bare minimum.

Not something that can be powered via the fag lighter socket. Will need wiring in directly to the battery via suitably sized wiring.

D.

At only 36x4=144 watts out, it would have to be a horribly inefficient charger (hot) to require more than double that at the mains input, but yes, I agree, it's a sizeable inverter. I'd guess a quality 300w inverter might be sufficient.

Just gone through this myself - got an inverter to charge a Shimano eBike battery from my van's leisure battery.

Your charger requires 345 watts (230 volts*1.5 amps). You'd want some headroom too, and note that it would require an inverter to produce that for a sustained period of time (some cheaper inverters' advertised power ratings are based on the maximum surge they can produce, so best to check).

You'd be looking for something around 500-600W, and as above, you'll need to wire it straight to the battery and not through cigarette lighter, as 345 watts @ 12 volts is 28.75 amps (so you'll need to have it fused above that).

My Shimano one requires 625 watts, so I got a 1200W Bestek inverter - around £75. The extra headroom can't hurt and it has two sockets so I can charge other things too (battery for my Hydroshot power washer etc)

Surely there is a market here for 12v ebike chargers?

Surely there is a market here for 12v ebike chargers?

Seems there is

https://www.e-bikeshop.co.uk/blog/post/bosch-ebike-12v-travel-battery-car-charger/

EDIT. The product doesn't seem to exist any more on that website though...

Your chargers output rating, 4 amps at 36v (144 watts) is only going to be reached when the battery it is charging is fully charged, and at that point, there is a very good chance the charge current will be being tapered by the charger (to avoid cell imbalance)

So, for most of the charging period, the charger is likely to be pulling significantly less power than that peak rating. Allowing for a 80% charger efficiency (typical worse eff) you need around 175 watts at the input, which is 0.72 amps at 240Vac.

If you allow your inverter to also have an 80% efficiency, input current at 12V is 14 amps, which is a bit too much to pull continuously from a normal cigarette lighter adaptor ime.

However, i suspect a 200W inverter would actually work, and a 300w one will deffinately work, but either would need a decent 12v dc feed from the battery, and ideally probably needs the engine running so the alternator is charging (which also boosts vehicle voltage to around 14.3v, so reduces currents a bit)

It's definitely a better option to buy a dedicated vehicle charger for your battery if one is available.

You are converting 12v DC to 230v, and then back down to 36v, both of which is inefficient. Also not all chargers are tolerant of invertors so there is a small risk you will pop the mains charger.

If you do go the inverter route, pure sine wave is best, modified sine wave is a poor substitute, if it doesn't state either of those it will be a very poor quality output.

Surely the ebikes battery has a larger capacity than the car battery....?

So you can only really charge it whilst driving or running the engine...

Just to add, if you are planning to charge it from a car battery them it'll flatten the car battery pretty quickly. If you plan to charge it when driving then you should check the alternator can handle the extra load.

Agree that you probably need to charge it whilst driving. Alternator should be fine, they are designed for high loads and campervan owners regularly connect up 30-50 amp battery chargers to them 🙂

The Bosch 12v charger has been discontinued and is rare as hens teeth. It's also only a 2A charger. I've found one on eBay for £170.

I'd be charging whilst driving, if at all, on the drive back from BPW for example as it passes FoD so I could stop off for a few runs there. I have an inverter already, but I wasn't sure if it would be powerful enough. I don't have a camper van though, so I'd need to check my alternator was man enough too.

a 12v 2A charger will take a lifetime to recharge the e-bike battery.... maybe if you are driving via Paris to FoD from BPW it will be charged. No wonder they don't bother selling them.

Can you not just buy a spare battery and swap them?

The charger input of 1.5A @ 230V is the inrush rather than continuous current, however you want to size the inverter for that anyway and look for something 350W+.

You'll need to wire the inverter directly to the battery or fuse box as it's power demand is too much for a cigarette socket which are typically rated for 6A maximum continuous current. The charger is going to spend a chunk of time pushing out 3-4A which is >120W and becomes >>10A @ 12V when you add in power loss in the charger and inverter.

I'd be surprised if the charger is not rectifying the input and therefore insensitive to the shape of the waveform it receives (sine wave or not) but cannot tell for sure without researching / taking one apart.

Amps multiplied by volts will give you the number of watts produced.

Only for DC and resistive AC loads.