E-Bike Battery Charging on 12V (1 Viewer)

Feb 5, 2009
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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:
Broken Link Removed

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
 

Don Quixote

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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:
Broken Link Removed

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
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.
 

Lenny HB

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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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EssexBoy
Feb 5, 2009
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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.
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...
 
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EssexBoy
Feb 5, 2009
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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.
Thanks @lennyhb @Don Quixote
Sounds like I might have been trying to be too clever for my own good then...
 

Snowbird

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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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Sep 24, 2013
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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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EssexBoy
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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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EssexBoy
Feb 5, 2009
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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
 
Sep 24, 2013
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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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rupert

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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
 

BwB

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

Welsh girl

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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.
 

Lenny HB

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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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You need one of these ! (y)
9c1ea52cad72d916483b903e51ddd522--power-generator-off-grid.jpg

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bobandjanie

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We charge 2 electric bike batteries on the move, we have a 50amp stirling b2b and a 600w stirling pure sine wave inverter they pull 400w at the start and that drops as they charge. (y) Bob.
 
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That said charging of lithium batteries is pretty simple and only needs a constant current, constant voltage charger.

It may be simple to an electronic design engineer, but it's by no means simple to the average practical motorhome owner. I think it could be easily misinterpreted in a way that could cause real danger. So here's a bit more information.

A lithium battery charger charges in two stages. It starts in constant current mode. The fixed current is decided by the size (ie total capacity) of the battery. The voltage is constantly monitored: it slowly rises as the battery charges. When it reaches a pre-defined level (decided by the battery chemistry and ideally temperature as well) the charger stops constant current mode, and swaps over to constant voltage mode.

At this point it's about 80% charged. The constant voltage level is decided by the battery chemistry and ideally temperature as well. In constant voltage mode, the current is constantly monitored as it slowly falls. When it drops to a value in Amps that is 3% of the Amp-hour capacity of the battery, the charger stops the charging process and switches off completely. There isn't any 'trickle charge' mode like you might use with lead-acid batteries.

So, yes, a lithium battery charger contains a power supply that can switch between constant current and constant voltage mode. But it also needs an accurate voltmeter, current meter, switching circuitry and programmed intelligent controller as well. It also needs to know beforehand what the battery capacity is, and exactly what chemistry variant it is made of.

You may think that's pretty simple, but if a typical enthusiastic funster takes your words at face value, they are, quite literally, playing with fire.

Overcharging a big lithium battery in a vehicle with fuel and gas systems, with people sleeping, often in remote locations, just cannot be a good idea. Use a proper charger designed for the battery you want to charge.

Of course if you're an experienced hobbyist and think all the above actually isn't so difficult, then by all means knock up your own custom 2-stage charger.

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JockandRita

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Of course if you're an experienced hobbyist and think all the above actually isn't so difficult, then by all means knock up your own custom 2-stage charger.
Having a respect for the potential dangers, I have to say, it wouldn't be for me. :(

Cheers,

Jock. :)
 
Sep 24, 2013
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I remember making a small lithium ion charger for my daughter when she went back packing in the USA. But that was only for her phone when she was off grid. It also used a stand alone dedicated integrated circuit. I would hesitate to think about doing one for a large capacity bike battery even with 40 years electronics experience.
 

Don Quixote

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I remember making a small lithium ion charger for my daughter when she went back packing in the USA. But that was only for her phone when she was off grid. It also used a stand alone dedicated integrated circuit. I would hesitate to think about doing one for a large capacity bike battery even with 40 years electronics experience.
All the phones need is a stable 5vdc or whatever, all the charger electronics are on board the phone.
 

Don Quixote

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All the phones need is a stable 5vdc or whatever, all the charger electronics are on board the phone.
I was pointing out - the phone is fitted with lithium batteries ! of which something charging wise went wrong EVEN at 5Volt...................

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Apr 22, 2013
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I am on my first trip away with my Bosch Ebike, currently charging it using our 1500W inverter. What happens is the inverter draws 1amp when switched on but doing nothing, when the charger is switched on the current draw increases to 2amps i.e. One for thr inverter and one for the charger. This remains the case for about 20 seconds while the charger works out the state of the battery. Then the currents increases to 12amps as charging commences. The current taken by the charger slowly drops during charging ending up at barely 4amps near the end of charging (i.e. 1for the inverter and 3 for the charger).
Make of that what you will but as the charger is a "slow start" device and peak take in about 11amps a 150W inverter should do. I have a pure sine inverter and would always recommend one.
I have a birthday next month and a Bosch 12V charger is top of my birthday list. I'll report on that later.
 
Apr 23, 2010
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I have a bosch 12v charger and tend to use it whilst travelling to charge batteries up,or if parked a nice sunny day and let the solars replenish hab batteries.
Fortunately lithium batteries can be charged at any point as they don't require memory to top-up.
Ace piece of kit by the way(y):)
 

Lenny HB

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I have a bosch 12v charger and tend to use it whilst travelling to charge batteries up,or if parked a nice sunny day and let the solars replenish hab batteries.
Fortunately lithium batteries can be charged at any point as they don't require memory to top-up.
Ace piece of kit by the way(y):)
I looked at them, expensive and only charges at half the rate of the mains charger so I went for a pure sinewave inverter. I can charge both batteries in a quarter of the time it would take with a single 12v charger.

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