Inverter/Power Pack

[BarleyRiser]

I'm looking for a way to charge ebike batteries in my campervan. What power do I need from an inverter or power pack? I assume it's the input that counts, so would a small 150W do the job?

One charger gives the following information:
Input: 100-240V 50/60Hz 90W
Output: 36V 2A
The other gives:
Input: 100-240V 50/60Hz 2.5A
Output: 42V 2A

 

[StuartsProjects]

Its not clear what you are intending to use to power the chargers, or which batteries you want to charge.

If the campervan is on mains hookup, just use your normal (mains powered) charger.

 

[BarleyRiser]

Looking for a method of charging when not in EHU. So, as I said, using an inverter or power pack.

Batteries are 36V 8.8Ah 317Wh and 36V 5.8AH
Surely I just need to check there is not more than 150W drawn. I know they won't run a kettle etc but it's not clear to me how many watts these chargers take.

 

[sjpt]

Chargers are typically 2amps 36v 42v (output to battery) so 72w 84w. Allowing for inefficiencies maybe 100w.
Of course more for fast chargers (often 4 amps), or chargers for higher voltage battery.

If you will be charging off a normal car battery beware; it's capacity is probably not that much more than the ebike battery; maybe 70ah 12v so 840wh. Allow for the inefficiencies of the inverter and the charger. A charge off even your relatively small ebike batteries will make a big hole in the car batter charge.

p.s. Correction after reading the following posts, of course the 'typical' 36v charger is at 42v. Doesn't change the conclusion.

 

[Benjahmin]

This is something I've been looking at and I'm not sure the numbers stack up.
I think the thing to look at is Watt hours because this gives you capacities.
Your two bike batteries amount to about 523Wh, that's what it would take to charge them from empty - nominally.
Assuming a 90Ah 12v leisure battery, that is 1080Wh. Lead acid batteries don't like being deep cycled so I'd say only about 75% of that is realistically available to you.
Then add in the inefficiencies of inverter and chargers and you are near leisure battery limit.

Your second charger, with an input rating of 2.5A, works out at 600w by my maths. So no a 150w wouldn't do.

There is a thread running on solar charging - this may prove more fruitful.

 

[StuartsProjects]

Output: 36V 2A
Output: 42V 2A

Its likley, that if the '36V' charger is for an eBike battery, then it will be providing 42V @ 2A to fully charger the battery. Thats;

42V * 2A = 84 Watts.

Now the charger will use some power itself, it will 'only' be around 85-90% efficient. Thus it will need about 93-98 Watts of power input to provide the 84 Watts into the battery.

So you need an inverter providing say 98 Watts minimum. Perhaps a 100W inverter is not a good choice, it will be running at near maximum power for some hours.

A 150W inverter seems a better choice. But then dont be tempted to connect other mains stuff whilst the eBike batteries are being charged.

 

[StuartsProjects]

The other gives:
Input: 100-240V 50/60Hz 2.5A
Output: 42V 2A

Even at 100V 2.5A power input would be 250W, yet the power out is only 84W.

These chargers are most normally switched mode, so power conversion efficiency is around 85% +, so circa 100W in for 84W out.

 

[cyclebuddy]

I used this one in my VW T5 for a while to charge e-bike batteries off the 100Ah starter battery. It's pure sine wave, better/kinder than modified square wave. It depends what fusing you have as to what you can draw off a 12v socket, but typical 10A fusing allows a 100w load which is enough for many e-bike chargers (my T5 was 15A). To get the full 300w it needs wiring direct to your battery. It worked well, but as others have mentioned, it does take a lot of energy out of the battery by time your bike is fully charged (I've since added a dedicated battery and solar).