Charging Electric Bike Batteries When Not On Electric Hook Up (1 Viewer)

Phil J.

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Dec 21, 2014
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Hi,
I have searched for some help but can't really find the answer I need:

I have the following:

2 x 36 volt 10ah electric bikes
2 x chargers. Input - 240v ~ 1.8A max, Output 42v - 2.0A

The motorhome has:
2 x 85ah leisure batteries (new)
1 x 100w solar panel
1 x 1000w quasi sine wave inverter

My problem:
I tried charging both batteries together on the inverter and the battery low warning came on before both were fully charged but it was a bright but not sunny day. Overnight, as there had been little sun during the day, the batteries were still very low but everything worked fine during the day. As we were again off EHU for a few more days we decided to play safe and have a night on EHU and get fully recharged. All fine again but didn't risk recharging the batteries for the remainder of our trip on the inverter and managed to get the bike batteries recharged on mains at the site wardens caravan (the site had no EHUs for other motorhomes or caravans).
As a by the way, my solar set up keeps my motorhome going more or less indefinately when just using the normal stuff - satellite tv for maybe an hour or so a day, low consumption led lights, water pump, etc.

Should I have charged 1 bike battery at a time on the inverter during the day?
Is my set up sufficient to charge 1 or 2 bike batteries?
Does anyone else have similar who can share their experience?

Thanks in advance for any help.
 

hilldweller

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36V * 10Ah = 360Wh * 2 = 720Wh.
12V * 85Ah = 1020Wh * 2 = 2040Wh

You normally use only 50% of a leisure battery = 1020Wh.

So your two bike batteries, with all the electric losses are as big as your leisure battery. And that assumes you have fully charged leisure and no other load.

OR.... You have 5litres of fuel and a 6 litre tank to fill.

If it's any consolation we are in the same boat.
 

Don Quixote

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Not long enough, but a little common sense helps..........
Well firstly your inverter will draw 83amps at full power. Secondly you have 2 x 85amp (total 170amps ) batteries, but really you only have 85amps to play with as once you discharge them past 50% you are starting to destroy them. You say/have "2 x chargers. Input - 240v ~ 1.8A max, Output 42v - 2.0A"= total 4amps per hour. Why do you have a 1000 watt inverter when all you really need is a 500watt one. More than enough to charge the bike batteries, but will draw 1/2 the amperage or less.
The solar panel should do the job, but you only need 2/3 days of no FULL sun and your batteries will start to go past the 50% charge mark and therefore start to die............
Remember that you are already drawing 4/5amps per hour with your TV, Sat etc....... then plus another 4 amps for recharging bike batteries. Start watching TV at 5pm until 10pm and charge batteries will draw total = 45amps = two days later batteries are below 50%.
Going onto EHU for 1 x night will NOT fully charge your batteries................
Hope that helps.

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Don Quixote

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Not long enough, but a little common sense helps..........
36V * 10Ah = 360Wh * 2 = 720Wh.
12V * 85Ah = 1020Wh * 2 = 2040Wh

You normally use only 50% of a leisure battery = 1020Wh.

So your two bike batteries, with all the electric losses are as big as your leisure battery. And that assumes you have fully charged leisure and no other load.

OR.... You have 5litres of fuel and a 6 litre tank to fill.

If it's any consolation we are in the same boat.
GOOD POST.
 

DBK

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I see Lidls are selling a generator for £149.00 at the moment....


But don't worry about your inverter drawing twice as much current as a 500W one, both will, within a gnats, draw the same current for the same load.
 

Judge Mental

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I see Lidls are selling a generator for £149.00 at the moment....


But don't worry about your inverter drawing twice as much current as a 500W one, both will, within a gnats, draw the same current for the same load.

is it one of the ever so noisy ones?...really like those!:giggle:

this where Bosch powered bikes come into there own (yet again) a full charge from empty only takes 2.5 hrs and a partial charge a lot less....

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Feb 24, 2013
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not long enough
we charge anything requiring more than a couple of A's while on the move, the leisure batteries are being well topped up by the alternator, we then have a plug in power supply / charger for the laptops and bike charger plugged in to the habitation and cab 12V sockets (y)

if not moving on, not sure what is best, run your engine while charging maybe? or move more often :)
 
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Phil J.

Phil J.

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Thanks for the replies guys.
If I am understanding Brian's calculations and the other comments, with my set up I should be able to charge one battery at a time? I also understand it is better to top the bike batteries up every time we use them as this will take less time to charge and, therefore, less drain in one go from the leisure batteries. The other thing is - with the extra(?) power of the alternator when on the move with there be sufficient charge going in to charge both batteries at the same time?
Sorry for all the questions but I want to make sure I'm not overdoing the draw on the leisure batteries which may cause premature failure.
Thanks again for all your help - really appreciate it.
 
Apr 23, 2010
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Hi Phil J,we had a similar problem but 3 e-bikes,260amp/hr of L/battery,90watt solar panel and a 500watt pure sine inverter.
The solution for me was fit a B2B which keeps my leisures nicely topped-up,and charge 1 battery at a time when travelling as then there is no drain on the L/B's,easy enough to check them if fully charged then swap to the next one.
Keep the e-bike batteries in the front of the van and the co-pilot does the monitoring!!(y)

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Aug 6, 2013
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Well firstly your inverter will draw 83amps at full power. Secondly you have 2 x 85amp (total 170amps ) batteries, but really you only have 85amps to play with as once you discharge them past 50% you are starting to destroy them. You say/have "2 x chargers. Input - 240v ~ 1.8A max, Output 42v - 2.0A"= total 4amps per hour. Why do you have a 1000 watt inverter when all you really need is a 500watt one. More than enough to charge the bike batteries, but will draw 1/2 the amperage or less.
The solar panel should do the job, but you only need 2/3 days of no FULL sun and your batteries will start to go past the 50% charge mark and therefore start to die............
Remember that you are already drawing 4/5amps per hour with your TV, Sat etc....... then plus another 4 amps for recharging bike batteries. Start watching TV at 5pm until 10pm and charge batteries will draw total = 45amps = two days later batteries are below 50%.
Going onto EHU for 1 x night will NOT fully charge your batteries................
Hope that helps.
A smaller inverter will save a small amount but it won't save anywhere near "1/2 the amperage". All inverters draw a very small current when not in use and when they are in use this is added to whatever current is being drawn when loaded. This small current is slightly higher for a larger inverter but it's still small.
 

Don Quixote

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Not long enough, but a little common sense helps..........
A smaller inverter will save a small amount but it won't save anywhere near "1/2 the amperage". All inverters draw a very small current when not in use and when they are in use this is added to whatever current is being drawn when loaded. This small current is slightly higher for a larger inverter but it's still small.

I fully aware of that fact, however my point was why have 1000watts to charge the bike batteries when a 500watt will do the same job. A saving on batteries is a saving no matter how small..........

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Apr 9, 2014
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this where Bosch powered bikes come into there own (yet again) a full charge from empty only takes 2.5 hrs and a partial charge a lot less....

Not one for expensive ebikes, but quite impressed with 2.5 hrs charge time, mine take 5hrs, also I notice that Bosch and a couple of other suppliers have 12v Travel chargers, which would presumably be more efficient rather than using an Inverter and a 230v charger.
 
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Phil J.

Phil J.

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Dec 21, 2014
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Thanks everyone for your input - you can always rely on Funsters to help!
I am going to adopt the following on our next trip (and if it works it may be a good policy to adopt for other ebike owners in the same situation):
  • Charge where possible on the move - one battery at a time
  • Top up batteries every time they're used
  • When topping up batteries on the inverter (one at a time) do it half way through the day so the leisure batteries have had a top up on the solar and have time to recover after - best when the sun is shining
  • Don't charge both batteries at the same time and don't leave them too long before recharge
By the way the reason I have a 1000w inverter is because it was already fitted when we bought it.
We're away again a week on Friday for a couple of weeks sans EHU so I'll test the theory and, of course, report back.
Thanks again Funsters
 
Jun 18, 2008
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Can you recommend a good inverter to use while travelling for topping up via the cab cigarette socket ? (If I recall correctly the socket is 150w )

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Phil J.

Phil J.

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Our inverter is a 1000w purchased originally from Roadpro. As I mentioned in an earlier post ours was already fitted when we bought our moho. However, as we spend most of our time without mains we've used itvquite a lot. I understand the problem is that the smaller ones are only good for charging very low voltage stuff that can normally done though a usb. The other thing is that there is always the risk of overloading the wiring to a cigarette socket where as the independent inverter from about 350w upwards is wired direct to your leisure batteries with heavy duty cable and can also be run whilst driving.
Hope my thoughts help.
 

Don Quixote

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Not long enough, but a little common sense helps..........
Can you recommend a good inverter to use while travelling for topping up via the cab cigarette socket ? (If I recall correctly the socket is 150w )
Thats around 12.5amps load, but even though it says rated at 150watts I would be careful. To be honest I would wire it to the battery with an inline fuse.
 
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Phil J.

Phil J.

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That's where I'm coming from Don. Many don't realise the danger of overloading the electics.
My inverter has wire about 5mm thick direct to the batteries with a fuse. I would also say having had to tidy up the electrics on ours it's a fairly simple job to install to the leisure batteries.

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Last edited:
Apr 26, 2014
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We have the following charger 20150825_135329.jpg and would like to charge e bike on the move. Also require something to charge laptop. Can anyone recommend an inverter please ?
 

jumar

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Our solution is dont buy electric bikes, keep peddling whilst you can, then you only need to recharge yourself.
And thats a pleasure in itself. :LOL:

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Apr 26, 2014
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Our solution is dont buy electric bikes, keep peddling whilst you can, then you only need to recharge yourself.
And thats a pleasure in itself. :LOL:

Great idea but unfortunately Sue has arthritis so struggles on a proper bike.
I'm still peddling well though.
 
Jul 12, 2013
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Thank you all for the solutions to this problem. I did notice that after driving with the inverter on, charging my two batteries, when I stopped driving and went on hook-up (well it was free) the dial on my meter went into overtime for a short while.
 

pappajohn

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One charger will draw almost 40 amp/hour from your batteries via the inverter.

1.8a at 230v....35a at 12v....plus losses and other appliances, lights, water pump etc.

Multiply that by 2 and you draw 75 to 80 amps each hour.

Your two hab batteries will last one hour before 50% discharge (safe limit)

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DBK

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One charger will draw almost 40 amp/hour from your batteries via the inverter.

1.8a at 230v....35a at 12v....plus losses and other appliances, lights, water pump etc.

Multiply that by 2 and you draw 75 to 80 amps each hour.

Your two hab batteries will last one hour before 50% discharge (safe limit)
I don't think you can use the charger figures, which are maximums, as a guide to how much energy is required. @hilldweller explains it well in post #2. If you want to be a bit more accurate assume the efficiency of each link (other than the leisure batteries) is say somewhere between 80% to 90%. So using rough figures and doing the sums in my head the 36 Ah batteries need say 40 Ah to charge them. The chargers have losses so the input might be say 45 Ah then add the inverter losses bringing it up to at least 50 Ah.

Now you've only got a safe 85 Ah before your batteries are discharged as far as safely. Thus if you try and charge both batteries, which requires 100 Ah you will get the warning signals you got.

The solar panel will help but lead acid batteries have poor charge efficiency, perhaps 50% to 70%, in other words the 100W solar panel isn't going to do much on a dull day to recharge the leisure batteries although it will make a contribution to the immediate load but it might only generate an average of 4 amps over 8 hours when the sun is above the trees. This only contributes an absolute maximum of 50 Ah and more realistically it could be a lot less.

Add in the other loads and you can see why charging even one battery is probably the most you can expect and you won't be able to do the same the next day as the batteries are not going to be recharged over night.

As suggested a B2B charger or generator would be a solution but it will take several hours and only you can decide whether the noise and enforced idleness are worth it.

I think you need to be on EHU or have at least 300W of solar, or drive for a few hours every day, or, more realistically, use the bikes only lightly and top them up at every opportunity!
 
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I agree with DBK who has hit the nail on the head. In my opinion the OP really doesn't have enough resources to recharge e-bike batteries with his current set up while off grid. Especially during winter months the 100W panel will not contribute much even on a good day and 2 x85AH batteries are really the minimum needed for normal habitation use without using that power to recharge electric bike batteries of any size. Probably the cheapest way would be to use EHU every time you need to recharge the bike batteries. If that's not practical then look at ways of boosting your set up by either B2B charger, larger habitation batteries and additional solar. I'm not sure that a portable genny would be the answer as it uses the on-board charger (usually around 18amps) to charge the habitation batteries and would take several hours to replenish them although it would allow you to charge the bike batteries through the 240 v sockets (assuming the neighbours didn't get too irate) .

We charge our bike batteries while on the move using a Sterling B2B charger and inverter as our 250ah habitation battery isn't enough. I don't know if this applies in this case but a point to consider is that when charging some of the newer lithium bike batteries you can get up to 80% charge in the first two hours but the last 20% also takes up to two hours - if power is a premium then perhaps you could forgo the last 20%
 

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