solar 12v vehicles as solar portable generators

[createthis]

I've been doing some research. No research is perfect, so feel free to correct me if/when I miss something. I've noticed that "portable solar generators" (think: goal Zero Yeti line) tend to be 12v. Also, e-bikes and skateboards tend to be 48v.

I was thinking... what if I combined the two somehow? A vehicle that was also a fully functional portable solar generator, in other words. I mean, that vehicle, when it's sitting still, is a giant battery. Seems like it would be handy to be able to use it to power things like laptops and cell phones.

First, I tried designing a 48v solar generator. I ran into trouble at the 120v inverter. Most small inverters ( less than or equal to 1200 watts ) take 12v input. I think the big expensive heavy Outback residential solar lineup has an inverter capable of running off a 48v supply, but I couldn't find anything smaller. So, basically, you can build a 48v solar generator with an ebike motor, but you can't plug your laptop into it unless you lug around an expensive and heavy Outback inverter, or you build your own from scratch. Boo.

Ah-ha, I thought. Fine. I'll make it all 12v. So, the solar generator becomes relatively easy. LifePO4 batteries to save weight. Some kind of BMS so they don't burn. A couple of light weight Genasun charge controllers. Any off the shelf 12v inverter, like a Xantrex ProWatt or something. No problem. But now, I get stuck when I want to drive the motor. Most e-bike motors want 48v so they don't overheat from all those amps. I looked around for a 12v to 48v dc-dc boost converter, but I couldn't really find anything over 200 watts off the shelf. Also, there are losses with a boost converter. 80% efficiency or so, right? So yeah, I know I could engineer one, but probably expensive, heavy, and lossy. Boo.

So, I was thinking... if I have 4x 12v batteries, I can arrange them in series for 48v and parallel for 12v, right? Is it possible to design a relatively simple circuit that allows me to do both at the same time? For example, I'd like to be able to charge at 12v and run a 12v inverter and drive a 48v motor. I'm not an electrical engineer. I have some basic electronics theory under my belt, but I don't think I've ever seen a circuit that can do this. It kind of hurts my brain thinking about it. Is it possible?

Thanks,

--
Jesse
CreateThis.com

 

[Nobuo]

Welcome!

I think you thoughts are right. It is something possible, but there are some obstacles to beat that maybe could not worth the time / costs.

So, for example, you have 4 units of 12.8V nominal 4s LiFePo4 packs.

One basic cost obstacle is that you need to install a 4s BMS to each pack, those BMS are not too much used and will have a relatively high cost.

Then you are forced to charge the battery with a 14.4V LiFePo4 charger, the whole 4 packs connected in parallel (I don't suppose you want to charge each pack separately) in order to have right balanced cells during the charging through each 4s BMS.

so..

We could imagine for example, that you want to achieve a minimum reliable capacity of 12Ah on your 51V(16s) LiFePo4 battery, result of serialing all 4s packs, for a standard ebike range and use. That makes that when you will charge the 12.8V 4s paralleled packs you need to charge 48Ah. So the need of using a reliable minimum of a 14.4V 10A charger would be another cost obstacle.

Another difficult is the circuit that makes 4s paralleled into 16s and vice-versa. Each time you change the circuit to 16s, a spark is made, so there is a wear out of the realys on the circuit, being those relays needed also not cheap. There is another difficult about the dangerous of not having the right voltage output when charging. Maybe two different discharge ports would be needed.

In my opinion, this is more simple if you just have your 48V or 51V pack and use a 48V inverter. I am precisely working on a solar small installation at 48V and a 1000W - 2000W peak inverter is not extremely more expensive than 12V - 24V ones.

For example this one, that I have and work hot but perfectly tested with 700W continuous

http://www.aliexpress.com/item/Free...nverter-12V-DC-to-110V-AC-USB/1787260005.html

For charging the 48V or 51V battery a 48V solar charge controller cost also more than 12V - 24V standard ones, but you can find them for less than $40 with configurable voltage charging outputs.

To make the 48V / 51V Solar panel voltage, just make a 4s serial 18Vmp / 21Voc panels in order to reach 72Vmp / 84Voc enough to charge any 54.6Vmax / 57.6max batteries.

Just one more appreciation, if you want to really save volume and keep safety batteries, is better to use lithium-ion NCA ones (x2 less weight) (x3 less volume), at the same or even lower costs than LiFePo4 ones.

 

[amberwolf]

Seems like it would be handy to be able to use it to power things like laptops and cell phones.

Many of their wallwart AC power adapters not only run on 115VAC, but also ~50VDC and up. Since most "48V" packs are actually 52-56V (or more), lots of stuff runs right off them.

Not all will, but a lot do.


For example, I'd like to be able to charge at 12v and run a 12v inverter and drive a 48v motor. I'm not an electrical engineer. I have some basic electronics theory under my belt, but I don't think I've ever seen a circuit that can do this. It kind of hurts my brain thinking about it. Is it possible?

The only "simple" circuit to do it is a relay set controlled by a switch. It's still kinda complex to wire and could be expensive for the parts, with risks of relays chattering under vibration while riding, and causing problems of various kinds. (unless you use heavier-duty relays whcih are probably more expensive, and even the other relays could be kinda large for using on a bike/etc. once it's all assembled).

It could be cheaper and simpler to use some sort of keyed connector block to convert serial (discharge) to parallel (charge), as is reasonably common to do with RC LiPo (there are threads about that, but I don't have any links).

The catch is, if you don't have it keyed so it can't be hooked up wrong, then eventually you (or someone) will connect stuff up wrong and damage something.

Another catch is while you have it wired for discharge, presumably you can't also charge it with power coming from the panels, wasting power generation capability.


So...it'd be better in a few ways if you can have everything work off the same voltage.

 

[dogman dan]

One guy here made a great solar trike, which takes a 24v solar panel and then uses a voltage converter to make it 48v, to charge a small battery and run the bike.

It should be very possible, to make a solar module that charges a 48v lithium battery with bms. Then you could swap a used pack for a fresh one, zoom off and while riding the other pack is solar charging.

 

[createthis]

So, what I'm hearing is that having both series and parallel wired up simultaneously will cause a short. Relays or mosfets might work as a switching mechanism, but wear and tear and efficiency are issues, respectively, as well as cost.

I guess another possibility would be to use an ac induction motor driven from the inverter. You'd be wearing out the inverter, incurring inverter losses, and ac induction motors seem to be a bit heavier than dc brushless motors for some reason, so you'd be adding weight. Seems like induction motors are less efficient than dc brushless motors too, but only slightly. However, if the primary goal of the vehicle is to be a solar generator, and the secondary goal is to be a vehicle, that might make sense. Doing a bit of research, I guess you'd need a VFD motor for speed control, which sounds kind of expensive to me.

Interesting info regarding motor efficiency comparisons: http://electronics.stackexchange.com/questions/58236/why-does-a-tesla-car-use-an-ac-motor-instead-of-a-dc-one

 

[amberwolf]

You'd also need a motor-rated inverter; some don't much like the inductive loads and go pop. :/