Off grid battery charging

Bikes4two

Esteemed Pedelecer
Feb 21, 2020
1,083
464
Havant
I'm looking to take my camper to non electric hook-up sites and am wondering how I might charge my ebike batteries, so fellow forumites, what might you suggest for this please?

The camper does have a 12v 100Ah lead acid leisure battery but no solar panels.

I know of inverters that convert 12v.dc to 230v.ac but my experience of such devices many years ago was that they 'eat' battery life but modern devices may be more efficient.

Amny thanks, Bf2
 

saneagle

Esteemed Pedelecer
Oct 10, 2010
8,892
3,988
Telford
I'm looking to take my camper to non electric hook-up sites and am wondering how I might charge my ebike batteries, so fellow forumites, what might you suggest for this please?

The camper does have a 12v 100Ah lead acid leisure battery but no solar panels.

I know of inverters that convert 12v.dc to 230v.ac but my experience of such devices many years ago was that they 'eat' battery life but modern devices may be more efficient.

Amny thanks, Bf2
What batteries are they? Normal Chinese ones can be charged from the 12v with a step up buck converter/ charge controller that you can buy very cheap from Aliexpress. If the battery uses comms, you need a much more expensive solution.
 
  • Like
Reactions: Bikes4two

Bikes4two

Esteemed Pedelecer
Feb 21, 2020
1,083
464
Havant
What batteries are they?
Oops, sorry, I should have mentioned that - standard 21700 and 18650 cells in self build 10s packs so standard BMS - no fancy comms or the like.

If I did produce 42v for charging, how do you achieve the typical CC/CV charge profile?
 

saneagle

Esteemed Pedelecer
Oct 10, 2010
8,892
3,988
Telford
Oops, sorry, I should have mentioned that - standard 21700 and 18650 cells in self build 10s packs so standard BMS - no fancy comms or the like.

If I did produce 42v for charging, how do you achieve the typical CC/CV charge profile?
Use a buck converter to step up the voltage from 12v to say 50v, then feed that into the charge controller, which steps it back down to 42v or whatever you set it to.

Buck converter:
DC-DC Constant Current Boost Converter 400W Step-Up Converter Voltage Regulator 8.5-50V To 10-60V for Electric Product - AliExpress
CC CV controller:
DC 6V-70V to 0-60V 15A 20A 900W 1200W CNC Adjustable DC Voltage Regulator CV CC Step Down Power Supply Module XY6015L XY6020L - AliExpress
and if your still nervous, you can always add a protection board:
XH-M604 Battery Charger Control Module DC 6-60V Storage Lithium Battery Charging Control Protection Board Switch - AliExpress

I'm sure that there are modules that combine the two functions, but I can't find them at the moment.
 
  • Like
Reactions: Bikes4two

cyclebuddy

Esteemed Pedelecer
Nov 2, 2016
1,671
782
Beds & Norfolk
The camper does have a 12v 100Ah lead acid leisure battery but no solar panels.
It's something I've done frequently; you can easily buy generic 12vDC to 42v chargers specifically for e-bike charging, or use the standard 230vAC to 42vDC e-bike charger with a small £40 300w pure-sine inverter from the camper 12vDC supply. It's not the inefficiency of conversion that you need to worry about (which in reality isn't too bad), it's the very limited capacity of your 12v/100Ah battery; if you work it out, you'll be able to charge say an 11Ah 36/42v battery maybe 1.5 times without crippling that by excessive DOD.

Even with a lot of van-roof solar, a much larger leisure battery capacity, and a very sunny day - assuming you want to park your van in the full-glare of the sun rather than the shade on a hot summer day - it's difficult to achieve off grid. I use 600w solar and 2 x 12v 280Ah (lithium not lead); one I know uses 900w solar and 900Ah on a very large camper to power the van and 2 e-bikes. Just one 12v x 100Ah will get you nowhere, especially if you're reliant on that to power the van too.

The best solution by far is to use on-site cafes, pubs etc where if you ask nicely they're mostly quite amenable to letting you recharge an e-bike battery or two.
 
  • Like
Reactions: Bikes4two and Woosh

Only-Me

Pedelecer
Nov 8, 2024
86
9
Hi I hope you don’t mind if I jump in here as my question is simular, I am looking to charge 20ah Ebike batteries off grid using portable solar kit the fold out ones but they seem very expensive atm so any suggestions would be appreciated.
My pal has an adapter that can use ev charge stations but I want to do some wild camping and charge so don’t mind waiting longer than the usual 4 hours .
 

matthewslack

Esteemed Pedelecer
Nov 26, 2021
2,510
1,639
The CC-CV behaviour is automatic, but entirely dependent on the accuracy and reliability of the device providing the 42V.The device can only supply its maximum current, which is the CC, and it is calibrated/set to 42V, which is the CV. If it fails, or if it is a more than 42V supply, your BMS is the only other safeguard against a battery disaster.


Your 100Ah 12V if run from full to flat is only 1200Wh, and allowing for 80% charger efficiency only gives 960Wh to the battery, and allowing for lead-acid hating being taken below 50% state of charge, really only 480Wh. Just not big enough for charging once you are parked up.

Two off-grid-van solutions: charge only whilst driving, AND get a minimum 4A charger otherwise you will always be driving, and solar. As @cyclebuddy says, cafes etc are the not quite off grid easier option.

Depending on the weather, each 100W of good solar will give between 100Wh and 700Wh per day, and through a boost charge controller like Elejoy MU400SP (about £30) 90% or so efficiency to the battery. More efficient that way than via your lead acid battery then charger.

My average solar harvest in UK conditions in the middle 4 months of the year (June 21 +/- 2 months) is around 300Wh per 100W, and I tow three 110Wp panels and ride every day.

If you consider solar, don't buy cheap 'semi-flexible' panels. They are prone to invisibly cracked cells which reduce output to almost nothing. SunPower cells only, and SunPower panels using their own cells are as good as you can easily get.

Often larger vans use normal rooftop panels which cost almost nothing these days, but are a lot heavier and not good for aerodynamics.

Permanently outdoors roof mounted panels are always working, so far better than something that is transported inside and only set up when parked.
 

matthewslack

Esteemed Pedelecer
Nov 26, 2021
2,510
1,639
Hi I hope you don’t mind if I jump in here as my question is simular, I am looking to charge 20ah Ebike batteries off grid using portable solar kit the fold out ones but they seem very expensive atm so any suggestions would be appreciated.
My pal has an adapter that can use ev charge stations but I want to do some wild camping and charge so don’t mind waiting longer than the usual 4 hours .
You need a fair amount of solar to keep charge times down. I tow a trailer and charge whilst riding.

If you plan to ride then camp for several days to charge, you can manage with a small system, but if you want to ride most days, you will need minimum of about 200W of panels. That's about 16 square feet. The 'how to carry it' question then arises!

My 330W trailer is 4ft wide, 6ft long and 25kg these days (6kg panels, 7kg 1000Wh battery, 1kg electronics, 11kg base trailer).

20220327_101030.jpg

Not everyone's cup of tea.