Hi all, I have a Specialized Crosstrail with a Bafang conversion, I've had it for nearly 5 years and love it. I holiday often in my motorhome and am planning a continental trip ( using aires ) during which I won't always have electric hook up to 240v supply. I don't want the expense of an inverter - any thoughts of how I could recharge the battery from the motorhome's 12v system ?
Charging whilst travelling in Motorhome
- Thread starter XianG
- Start date
You can buy e-bike chargers that run directly from a 12v vehicle/leisure battery. The bike battery still sucks a lot of 12v juice per bike charge, so unless you're using a decent solar array, occasional hook-up, or driving a lot of miles inbetween bike charges, you'll sap your vehicle battery(ies) to death very quickly.
The cost of these chargers is often £70-£100+... although they're more efficient, they're still more expensive than a £35 pure sine inverter.
The cost of these chargers is often £70-£100+... although they're more efficient, they're still more expensive than a £35 pure sine inverter.
Your generic battery could be charged direct from solar on your van roof using s suitable charge controller. Genasun is the leading brand, but come as fixed voltage so needs to be the exact right model, or see variable voltage model at 1/3 the price from ebikes.ca.
Ok, there's vat and p&p on top, but that's what I'm looking hard at.
240 volt portable Hyundai HPS-300 Portable Power Station | Generator Pro
Key Features Silent rechargeable power source: Charge your electronics on the go Ideal for camping or caravanning: Provides 600W maximum power and 300W continuous power Incredibly portable and lightweight at just 6.2kg:Easily fits into a backpack Easy to use: Monitor usage/battery life with the...
generator-pro.co.uk
As a general principle, what every power needs to go into the e-bike battery for a full charge, you'll need to provide at least 10% more power from your charging source (and that's assuming your charging source is 90% efficient).
My electrical theory is very rusty, so dear readers, please put me straight on what might be an over simplification:
My electrical theory is very rusty, so dear readers, please put me straight on what might be an over simplification:
- Let's say your battery was 36v rated at 17Ah, (36 x 17 = 612Wh)
- The formula for Power (P), current (I) and Voltage (V) is P=I x V
- So to me to get the same amount of power from a 12v source then you need to raise the current by 36v/12v = 3, ie. at 12v it's 3 x 17Ah = 51Ah to give the same Wh figure - and that assuming 100% charging efficiency.
- Now look at the capacity of for example, a 12v leisure battery - they are typically around 100Ah which in rather simplistic terms tells me that you will not even get two full e-bike battery charges from one fully charged leisure battery.
Your sums are fine. 51Ah x 12V = 612Wh.
My experiences last year with a Sterling Power 150W quasi sinewave inverter and my Shimano 1.8A charger was that battery to battery efficiency was about 60%, quite poor, so you need nearly double the leisure battery capacity to charge the bike battery. That's what is driving my search for some better way.
Charging whilst driving is fine as the alternator is doing the work, and nice big solar on the roof means you can charge at rest during the day. For riding every day I would want a second battery charging from the solar whilst riding with the first.
The reality is it doesn't work. This topic has been discussed to death on previous threads.
I tried a 100w panel on my VW Transporter, 100Ah battery, inverter and all the other guff. Even with strong sun, it's nowhere near enough in UK climes. A 100Ah vehicle/leisure battery gives you 1 and a bit 11-14Ah e-bike charges. The Lead battery won't recharge in a day even in a best case scenario. In America, they'll use solar arrays of 300-700w and a bank of storage cells (300Ah+)... in the desert sun. That works, but that amount of solar won't fit on my van roof... and it starts to get very silly cost wise.
Soundwave's suggestion of a power-pack is fairly common, but it itself is just a £500-£1000 lithium battery: You're simply transfering the energy from one device to another, then the donor is flat too.
The best option by far is to take the e-bike battery(ies) to a pub/cafe, buy a meal, and ask the staff for permission rather than just steal their power. I've not yet been refused. A faster 3A-4A-6A charger is way better than a standard 2A one, but that's quite cheap by comparison to the other available options IMHO.
More current will reduce battery life and not all cells used will like a 4 or 6a charge, it will depend on the cell spec's.
I'm slightly spoilt in my small van, as I have some LiFePO4 Valence batteries from a decommissioned electric van - 400Ah usable capacity, and I carry 200W of solar that lies in the sun whenever it can. They are not on the roof as it is rather curvy, so not ideal.
100W panel in the summer quarter of the year should provide 300Wh per day on average, lying flat on a van roof. A panel angled at 30 degrees and south facing should do that from April to September.
Many flexible panels are not good quality, and they are very susceptible to damage, which can only be detected by having a wattmeter monitoring performance.
I'd agree that most VW scale vans do not have an adequate house battery setup, but they have roof space for 200W of proper SunPower solar, which with minimum 200Ah LiFePO4 is a whole new ballgame. LiFePO4 has exceptional cycle life too, so an investment. Cheaper in the long run than lead.
Yeah, I hear what you're saying. The theory sounds plausible (as it did to me), but I actually tried it and it didn't work... at least not well enough IMHO.
Even doubling up solar and battery storage it's a marginal argument. There's also internal van space sacrificed, and a lot of extra battery weight and roof panel wind resistance to contend with. Fuel economy does go to hell. I prefer to keep it light and efficient.
The point is I could make solar work in my van, but it would come at too high a cost. I bought a faster charger and a second e-bike battery.
The bonus is - as a good pub customer - I sometimes get to park overnight in the pub car-park for free too. It's all win.
Even doubling up solar and battery storage it's a marginal argument. There's also internal van space sacrificed, and a lot of extra battery weight and roof panel wind resistance to contend with. Fuel economy does go to hell. I prefer to keep it light and efficient.
The point is I could make solar work in my van, but it would come at too high a cost. I bought a faster charger and a second e-bike battery.
The bonus is - as a good pub customer - I sometimes get to park overnight in the pub car-park for free too. It's all win.
And the BMS spec too apparently. I did check. The maker says mine will take a 4A charge rate. I think it's only Bosch that offers a 6A charger as an option?
The point is you want to be out cycling not sitting in a cafe/pub all afternoon still waiting for your batteries to charge, so if a recharge can be sped up even a little it's worth it IMHO.
tho i have not seen that 12v charger for sale for a long time now.
Bosch eBike 12v Travel Battery Car Charger – e-bikeshop.co.uk
New 'on the fly' 12v travel charger for Bosch eBike battery packs. Today we announce the new 12v car cigarette socket charger available for 300Wh & 400Wh..
www.e-bikeshop.co.uk
found one but not cheap.
eBIKE BOSCH TRAVEL BATTERY CHARGER ACTIVE PERFORMANCE 12V DC-DC 0275007914 UK | eBay
Ideal for battery charging while travelling. This is available for download from global Bosch web site in many available languages. also see LED. This is now discontinued by Bosch, so quite rare and hard to get hold of.
www.ebay.co.uk
Just to update this thread since things have moved on a little (for anyone coming back here)...
I know @matthewslack has since developed a really good mobile solar trailer for his extended cycle tours, and continues to develop that...
For my own part, I did say to hell with the cost, and succumbed by buying a Bluetti EB70 716Wh LiFeP04 mobile battery pack and 2 100w SunPower solar panels, which along with my 2 e-bike batteries and 3A charger gives a wide spread of charging options for my own cycling adventures away from home in my tour van... the Bluetti also providing power for my fridge, lighting, phone etc.
Funny how attitudes change!