charging from 12V

Thinking of taking a road trip, and bringing the ebikes. I am wondering about charging from the car's 12V system. I could just get an inverter and plug the chargers into that, but is there a more effecient way? I came across this on ebay 160309190010.

Thanks

I think plugging the chargers into an inverter would work fine. I've charged a big 12v deep cycle marine battery with an inverter and charger.

If I understand you right you are wondering about using the dc-dc converter as a charger. Did you notice that it's 100 watts?

You may need to run the car's engine of course. Or park on a hill if it's a stick. Chargers are pretty low wattage so as long as the inverter is big enough go for it. 300 watt inverters are still pretty cheap. It will work great for charging while you drive somewhere.

Inverters are like the biggest high loss device ever. The 400w Black and Decker i bought from walmart straight stucks. It takes about 40A 12v and converts io 115AC and can power up to 3.5A. I tried to tailgate with a plasma ad dvd player. It dropped my voltage to 11v in 3 hours. Barely crranked my car because of the voltdrop down below 10.5. Running the car was not an option. I had two optima batteries. Yellow top under the hood and a blue top in the hatch. Id hate to use the 700w. Granted my charger charges at 150W so its probably pulling 200 if not a little more from the wall. But a regular car battery is not going to charge you bike battery to full capacity. it will die within an hour or two if its just sitting not running. Inverters are made to use in a running vehicle. I had a 2000w that i used to run on my car but that car had a 225A altenator. That inverter was the size of a small car amp. and sucked power at about 150A. The only reason why i had it is because my house had alot of power outages due to construction and i just went out and cranked the car and ran an extention cord inside. I also did car stereo competitions... thats why i had the big alt.

icecube57 said:

Inverters are like the biggest high loss device ever. The 400w Black and Decker i bought from walmart straight stucks. It takes about 40A 12v and converts io 115AC and can power up to 3.5A.

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Around an 80% efficiency seems reasonable enough.

-R

Putting inefficiency aside for a moment its not to hard to work out what it will take to charge your battery's. lets say the average car led acid cranking battery is around 60ah at 12v and that you can depleat from it 50% of its capacity or 30ah to be safe and be able to start your car and not shorten the life of the battery.

So if you have for example a 36v bike battery that has a 10ah capacity it would pull 30ah from the 12v car battery + efficiency losses to charge from fully flat. If your charger is 90% efficient and the inverter 80% thats a 30% loss and you will pull a total of 39ah from the car battery.

I think you will be fine if you only charge while your travelling and stop charging when the motor is off. One option if your going into the countryside is to bring a small generator.

The best option You could just take advantage of opportunity charging from mains power.If your batterys/bms can handle it you can fast charge at at higher amps and perhaps charge your pack in a short time. a fast mains power charger could be just as cheep as inverters and voltage step up chargers + its usfull when you get home. If you are going on a long road trip you will be able to charge from the motel room.

I have been thinking along the same lines as i wanted to take our ebikes away fitted to a little teardrop camper van and travel around the place. My plan was to just get a powered camp sight and charge from that.

Kurt

Thanks for the input guys. The AH calculations are interesting. The Ping 36V chargers draw about 122 Watts so 240 for two. I think a 4-500 Watt inverter should work. We often stay at a B&B or motel on road trips, so I could charge there, I just like to be self sufficent, thats all. If I had an RV or camper van the roof could be all PV panels! Not going to work on the mini van though. I have one of those 12W 12V cloth backed folding panels but I figure it would take 6 of these in full sun to charge one battery at 2 amps, 36V!

Best,

Ecat

Yup, it takes a lot of panel. And ok, you would also have to drive around, or put a brick on the pedal. But the point I was trying to make, is you need to carry a big ass battery in the car to be able to charge from the car battery and still be able to start the car and drive off, not to mention the wear on the car battery doing a 100% discharge. Some folks just don't do the calculations and think they can charge with tiny solar panels, or a small cars starter battery.

The most practical way to carry charging is likely to be just to buy a small generator, but then you get to listen to the damn thing. A big deep cycle marine battery might do the trick, and then charge it back up when you get to the b&b or hotel if you want silence at the campsite.

some generators are very quiet.

I went for a ride on my ebike in the national park behind my house I went up to the lookout it was during the weekday so no one was around just the birds, snakes and so on. When I go to the top I could see there was just one guy doing some maintenance on some of the trail signs. It wasn't until I almost rode over it on my bike that I realised he had a small generator running. It was a little red Honda unit very very quiet. Most of the little ones are good for 700w.

Kurt.