E-Bike Battery Charging on 12V

Discussion in 'Tech/Mech General' started by EssexBoy, Jan 11, 2016.

  1. EssexBoy

    EssexBoy Funster

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    Hi All

    I'm hoping the electronics/electrical gurus out there can tell me if I'm on to the right thing to charge my ebike battery when off-grid...

    Basically, I'm trying to follow the advice to use 12V direct to power items where possible & avoid using inverters, and I though I could you this step up transformer to charge the 36V battery on my wife's e-bike:
    http://www.ebay.co.uk/itm/271560843172?_trksid=p2060353.m1438.l2649&ssPageName=STRK:MEBIDX:IT

    Now, on face value, this transformer looks just the ticket & would look like a straight "connect to 12V, connect to e-bike battery, job done", but I'm guessing its not probably as simple as that, so am looking for advice please. In a nutshell, would you do this?

    As background, I have 3x 110AH Hab Batteries & 200W of solar - and am thinking of B2B (but thats another story) - and move on every couple of days, so hope I should be OK on the 12V supply

    Thank you

    Steve
     
  2. Don Quixote

    Don Quixote Funster

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    Steve, I have same setup as yours plus the B2B and I use an inverter to charge the batteries ( we have 2 x eBikes ) whilst on the move and parked up. The solar puts the power back fine whilst static and the B2B works a treat when we are in the move. The item you have linked to looks fine, but how are you going to connect to charger? and how much heat will that produce stepping up current. Keep it simple I say.
     
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  3. Lenny HB

    Lenny HB Funster

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    I don't think it will work, most e-bike batteries have electronic circuitry that feeds back info to the charger about state of charge, temperature etc, the batteries will only get a proper charge using their own dedicated charger. Also by just using a power supply you have no way of controlling the charge current or voltage could be very dangerous with Li-ion batteries.
    Like John I fitted a pure sine wave inverter, not worth taking a risk, my bike batteries are £600 each.
     
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  4. EssexBoy

    EssexBoy Funster

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    Thanks @Don Quixote, much appreciated. I must admit I don't know how much heat it gives out so would need to do a test, I guess, before a full install.

    The current mains charger inputs 240VAC and outputs 36VDC 2A, so was just going to charge the battery direct from the transformer.

    My thinking was to have 12VDC->36VDC with the transformer rather than 12VDC->240VAC->36VDC with an inverter.

    As I say, I'm no where near an expert so thankful of the steer...
     
  5. EssexBoy

    EssexBoy Funster

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    Thanks @lennyhb @Don Quixote
    Sounds like I might have been trying to be too clever for my own good then...
     
  6. Snowbird

    Snowbird Funster Life Member

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    Maybe this will help. I looked at charging my 24 volt mobility scooters from 12 volt. I spoke to the mobility shop, who said they could sell me a dedicated charger for this job, but it would be cheaper to buy one on ebay. Like most other things just lately, I have not got round to purchasing one as yet, but they are available.
     
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  7. Lenny HB

    Lenny HB Funster

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    Bosh sell a 12v charger for their batteries, £150 and lower power than the mains one so takes nearly twice as long to charge.
     
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  8. stevec

    stevec Funster

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    Lithium ion batteries require a carefully controlled charge regime which the mains chargers provide. The one quoted won't have that. You also don't know how "clean" the voltage will be. These types of step up (boost) converters usually have an oscillator to produce AC then rectify it again leaving the possibility of some residual AC at the output. I did see reference to a 12V unit to charge 36 volt batteries but can't find the reference at the mo. I do know it cost about £100 and was a multi-type charger used for remote control models. Others may know the name of it.
     
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  9. EssexBoy

    EssexBoy Funster

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    Thank you for all the input gents...(y)(y)

    I should have known that my cunning plan wouldn't have been as cunning as I thought it was :LOL:
     
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  10. Big Nick

    Big Nick Funster

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  11. EssexBoy

    EssexBoy Funster

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    Sorry gents.. A follow up if I may please, as my maths are causing me an issue...

    When sizing an inverter, do I use the input or output figures coz the ebike charger says:
    Input is 240V x 1.5A which is 360W
    Output is 36V x 2A which is 72W

    My own logic says go with the 360W figure and get a 500W inverter, but seeing as I already have a 150W inverter, I thought I should check first.

    Cheers

    Steve
     
  12. stevec

    stevec Funster

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    I have a 400W inverter which I use to charge our ebike batteries. We have two chargers of different design although for the same type of bike. One of them works okay off the inverter, the other causes it to shut down. Charger is marked 140W at mains voltage. 36V 3A output. It's the start up current that causes the shutdown. One obviously is higher than the other.
     
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  13. rupert

    rupert Funster

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    my 36v e bike battery shows 42v when fully charged... so the charger must give at least 42v.
    i fancied the idea of charging direct from a 12v source but messing with these lithium batteries
    is dangerous as they have a habit of bursting into flames. so if your gonna play do it outside and don't leave it unattended
    best o'luck alan
     
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  14. BwB

    BwB Funster Life Member

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    use the input voltage. A 500w pure inverter should be fine.
     
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  15. EssexBoy

    EssexBoy Funster

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    Thank you gents...
     
  16. Welsh girl

    Welsh girl Funster Life Member

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    I've used a 300w pure sine wave inverter to charge our ebikes batteries ok.
    Once I did it when the solar panel was in strong sun through the inverter but now I usually do it on ehu.
    I guessed that trying to charge a 36v battery from a 12v battery was asking a bit much.
     
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  17. Lenny HB

    Lenny HB Funster

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    I use a 1000 watt pure sine wave inverter, enables me the charge both my 400 watt batteries at the same time, a full will hammer the batteries, so tend to charge then before they get too low and if possible in the morning on a sunny day.
     
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