# Charging electric bikes via an invertor

Discussion in 'Tech/Mech General' started by MikeandCarolyn, May 3, 2011.

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We're looking,tentatively, at electric bikes.So far they seem great if you are on EHU and can charge overnight,but what about when EHU is not available ? We have a 160w solar power,2x110 leisure batteries and a 350w invertor.Normally we achieve 100% charge by 10 am and then when we set off to our next Aire, or whatever, we use the invertor to charge anything that needs charging-Cameras/laptops.shaver etc.
What's the prognosis for charging 2x18ah bike batteries in the same way ?
I'm not optimistic I must say. Could this be a case for a Genny ? if so,what sort of power ?

Mike.

2. ### hilldwellerFunsterLife Member

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One vital missing figure - voltage.

18Ah x 24V = 432Wh x 2 = 864Wh Say 1200Wh
18Ah x 36V = 648Wh x 2 = 1296Wh Say 1800Wh

You have 2 x 100Ah batteries but you should use only half that.

Battery 110Ah x 12 = 1320Wh

So that's it, on 24V cycle batteries you would dump the whole lead acid into them, if 36V you could not fully charge the bikes.

160W solar is far too variable to really do any sums. You'll maybe get 100W for 5 hours on a brilliant day, so 500Wh, much less than a single bike.

A 1Kw genny will be fine if you can run it long enough but because the bikes take so long to charge not efficient. I would cherge on the inverter and half way run the genny to charge leisure because that charges much faster off the genny or hook up.

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Mike, I have been informed by Alan to have a look here and its not far from you.
http://www.tourdepresteigne.co.uk/

You can try out all the latest models and ask all the questions

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4. ### chrisboyo

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I don,t know about all this maths & watts stuff.
What I do know is that we went to france for 5 weeks with no hook ups and charged our 24v bike battries loads of times using a 150w inverter we got from Aldi

We have 2 80amp battries and a solar panal

Sometimes knowledge can be a dangerous thing

So there Mr Hilldweller!!

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Voltage-hypothetical at moment as bikes not yet purchased-something to bear in mind when choosing them I guess.
How much would the fact that we would probably be driving for around 4 hrs of the charging time change things?
So far it's not sounding very viable.

Mike.

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Sometimes ignorence is not bliss.
Im sure Mr Hilldweller can also work out how long it will take to destroy your batteries too
I think Mike is going about it the right way

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7. ### hilldwellerFunsterLife Member

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Huge improvement. I noticed our meter showing 16A into the leisure battery on tickover.

That's 200W x 4h = 800Wh

All these figures are intelligent guesses, you probably don't totally drain the bike batteries, though I do with my pathetic 24V 10Ah one. You will have other calls on your leisure battery of course. You're close enough to suck it and see unless you want belt and braces before you set off.

We're not *there* yet with electric power and you have picked the weakest link in electric transport - not having loads of electricity.

What you want in choosing a bike is the maximum Wh you can afford, so do the Amps x Volts for this. I've seen 48V in adverts which gives double the Wh of the average 24V battery. It's largely down to £££££££.

PS It goes without saying, buy only Lithium batteries. More energy per kilo than any other battery.

Last edited: May 3, 2011
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8. ### hilldwellerFunsterLife Member

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Shot yourself in the foot there Chris. YOU have the knowledge, which says it works ( for you ), I am taking intelligent guesses.

The real work conditions are so complex experience is by far the best way to solve this.

I think two batteries per bike would be brilliant, ride 'till battery one dies then turn round. Give or take hills you then get home.