Hybrid Kart Project

[shantanu]

Hello everyone, Im planning to build a Hybrid Go-kart for my college project.

Being from the Mechanical side, I lack a bit of electrical knowledge.

So, basically, my project involves four 12V 33Ah Batteries driving an electric motor coupled to the rear axle.
A petroleum powered 2-3hp motor coupled to an alternator which will charge the batteries on-the-go.

Now, My question is : What kind ( specs ) of an alternator will i need to charge Atleast 2 of those 12V 33Ah batteries ?
Is there any way to switch between charging 2 sets of batteries ? ( Toggling between Charging batteries A and B , & Batteries C and D )

I also thought of splitting the output shaft of the Engine to obtain to shafts that will give input to TWO alternators. But this will increase the cost and weight of the kart, so i dont think this option is feasible.

Any better suggestions would be welcome.
Thank You

 

[itsid]

Hard to say, yes you can toggle, but you'll need some big relais to do that, and that means you'll spend likely more money than you would for a second alternator.
(less weight though)

I assume you have a truck alternator providing 24V by what you said ...
Now the fun part, generally alternators produce alternating currents,
in a high voltage range (60 Volts or something) and are ramped down and rectified
to charge the battery consitently..
if you can open up the alternator, you might be able to modify it to provide you with twice the voltage and half the amperage.
(say you have a 24V 90Amp alternator, you'll be left with a 48V 45Amp alternator)

if you do not want to open it up, or the alternator does not produce a higher voltage than it provides,
you can just install a transformer in between.
"DC-DC step up" plans are on google
custom wound on say the transformer core of a microwave oven,
stay away from integrated circuits as good as you can, they'll fry on the amperages you're looking at

no need to split the PTO shaft btw, you can run both alternators with the same belt, just add two more tension rollers to have enough contact.

to see what alternator you'd need depends on the power of the motors..

but no more than 2237 Watts are even possible (due to the engine's power)

with 48V that's ~46.5 Amps with 24V that's ~93 Amps

'sid

 

[shantanu]

Thanks for the detailed reply Sid

I was assuming that the alternator came with a rectifier circuit ?
I have to yet go and check the market where they sell old components to decide which alternator i'll go for.

If you were in my shoes, what would you do best to charge 2 batteries considering Cost, weight and complexity as three major factors ?

To be honest, I suck at electricals. Have to do more and more research and brush up my fundamentals.

 

[Badot]

Car alternators generally do have the regulator/rectifier built in, but I'm sure there are examples otherwise.

Essentially I assume you're just going to end up with what amounts to a generator and battery charger mounted on an electric kart... so you may want to look into just buying a generator and a good 48v charger, and mounting it on the kart essentially as-is. Then you could run a household coffee maker as you drive too

Another thing that comes to mind... anyone know if you could hook, for example, two 12v regulators up to the same AC source in parallel, then run the outputs in series to get 24v? Makes sense to me but I've never tried, and motorcycle regulators may be a cheap, readily available way to do it assuming sufficient amperage.

 

[itsid]

yes, it's all build in.. at least the ones I've see so far had all build in.

But just because it's inside a case doesn't mean you cannot open said case

According to a chinese manufacturer for example the 12V alternator for a 1.3l Suzuki Swift is an internal 48V AC alternator..
(this one as an example)
ripping all out, leaving just the rectifier in place (well and the coils of course) should leave you with a 48V charging circuit.
the downside, it's only 70A @ 12V.. 840 Watts...
a bit low for your task I assume.

but asking google for a 48V alternator will show some hits,
maybe you want to take a look at some of them to get an idea what you are looking for.

well reducing the costs means you would want to go for one single alternator.
(two smaller ones are more expensive than one bigger unit.. at least if we talk about new parts here)
complexity, again, a single alternator, charging ALL batteries (the complete batpack at once) less hassle of connection, easier to maintain a clean route and no additional (and expensive) relais.

weight: well one alternator again, but the smallest possible one.
if you want the option to run the motors directly off the alternator you need as much power from it, as the motors are able to draw from a battery pack.
if you're okay to charge only half of the capacity back into the batteries you used while driving and the kart is allowed to sit and charge with the running engine for the same amount of time...
then half the amperage should be sufficient. (depending on your charging circuit that is )

Personally, I'd adjust the alternator to the engine (not the motors)
getting a lightweight alternator with say 1500W of power and mounting it to a 6hp engine is pointless... (exaggerated)
A 2hp engine will do just as nicely and is probably smaller and lighter too.

So, if you do not have an engine yet, first find your Alternator, then get the smallest possible engine that provides 125-130% of the power the alternator would need to produce.
(engine efficiency, even a belt uses power.. and it's good to not run an engine at full power to have a better fuel efficiency)

If you can, maybe a
small generator will be just what you're looking for:
like this here:
http://www.amazon.com/Champion-Power-Equipment-42436-1500-Watt/dp/B009E26LLC

an 80cc engine and a matching alternator directly mounted to it.. (yes 110V AC.. no biggie is it?)
or even more powerful and a tiny bit lighter...:
http://www.smallenginewarehouse.com/HHG-EU2000.html

something like that, all you need is a rectifier circuit with a 48V stedown and you're good to go.

PLUS: just in case you want it to be versatile.. you can keep the generator removable, to safe some weight on short trips, and have a nice generator at home in case you need it

'sid

 

[DeathMachine]

If you sized an AC genset just right, you could charge the batteries and run a small home window air conditioner, you'd have the first go kart with air conditioning!

 

[nayr83333]

look at battery switches that go on boats for switching between charging batteries A and batteries B. often boats have multiple batteries for starting the engine and running on board electronics and require the type of switch you are after.