Help regarding Alternators

[shantanu]

I'm working on my final year project. Building a hybrid Gokart.
So, I'll have a small capacity engine running 2 alternators ( 12V 40amp each ) and I'll be having a 1.2kW BLDC motor powered by four 12V 26amp batteries. Now my question is that is it possible to charge 2 batteries by one alternator ( each of the alternator chagrin 2 batteries at a time ) ?
Please provide a cheap solution if any.
Thank you.

 

[itsid]

depending on the size of your batteries .. yes.

but you will run into a serious problem..

to charge two batteries (12V each) with a 12V alternator you MUST connect them in parallel

to run the 48V motor from the batteries you MUST connect them in series!

See the dilemma?

'sid

 

[chancer]

Ok sid question: Is there a way to use switches to swap the wiring from parallel when "charging" during gas operation then switch to series for electric "run"

Besides: Is it really Fuel efficient? or hybrid. Can the kart run on the small capacity gas engine? then switch to run on the electric motor. The gas engine would have to run all the time to charge the batteries right. There is no such thing as perpetual motion anyway. The loss of gas horsepower for driving used to charge kills the efficiency. So then why not just ditch the electric and run on the gas? This is why Hybrid cars use heat energy created during braking to charge not the gas engine.
Please correct me if I am wrong.

 

[shantanu]

Thanks for the reply Sid.
Well, yes, connecting parallel won't be feasible since I need a 48v battery pack.
If only there were a way to switch from series to parallel everytime I needed a recharge

 

[chancer]

If you put two leads on each battery terminal and ran switches you should be able to switch from series to parallel. but you would need 4 switches and would it short circuit things if you could only switch one at a time, so as you were throwing switches half your bank would be parallel and half would be still momentarily in series, or vice versa?

 

[itsid]

Sorry but that's just nonsense...

carrying two alternators, a small gas engine and all that stuff around, when you need to stop, and wait for the batteries to recharge...

dead weight for most of the uses...

you'd increase mileage by reducing weight if you just carry a 48V charger with the kart and take your breaks at the next wall outlet


But yes, a series of heavy duty switches would let you switch from series to parallel...

but personally.. just flipping two terminals is the easier and cheaper option with the exact same result..

(there are quickchange terminals with a lever instead of a fixing screw )

But personally.. I'd rather get either premade 24V alternators from a truck or rework the rectifier inside the ones you have to provide 24V to do the same.

it's perfectly okay to run two alternators in series connecting just two of the four batteries you have splitting the 48V in 2 24V charging circuits.

All series, no switches.. and "on road charging"

'sid

 

[chancer]

I am afraid the thread starter is gone, and was just fishing. But I wonder if his project was actually hybrid. or just carries an engine for recharging purposes.
Would that even work as a hybrid. or do the alternators and battery weight make the thing so inefficient in gas mode that it would be useless.
Also I would think the project would have to be easily swapped from charging to driving modes by the operator at the flick of a switch. not by swapping quick change battery terminals. at least if he wanted a good grade.

 

[shantanu]

Still here mate.
I actually wanted it to be a series hybrid project ( charging the batteries on the go ). But finding a used alternator to serve the purpose is something I couldn't succeed at.
And the reason behind not being able to afford newer alternators is cuz we students are funding the project and we want to keep the cost as low as possible, anyway, guess I'll have to submit the theory behind the "hybrid" part than make it work practically. ( deadline in a week ).
Thanks for your replies, Learnt something new

 

[anderkart]

So, I'll have a small capacity engine running 2 alternators ( 12V 40amp each )

Something else you should consider here is alternators take between 1 to 5 HP (depending on their output rating) of the engines power to spin up to their max output. Alternators might seem super easy to spin over by hand when your standing there holding one, but not when they're working.

There's no free lunch there...

 

[itsid]

correct.. but for the alternators in question not too important... 600 watt each (estimated to be 80% efficient) of mechanical input at their MAX rate.. so a 1200 Watt engine (~1.6 HP) will do...

worst case: they'll need much longer to charge the batteries than you expect!

BUT:
twice the Voltage means twice the Wattage too..
so when/if you convert them to 24V they'll need almost the power anderkart talked about (~3.5 HP)
to have them charge the batteries as quickly as possible.

it'd be interesting to see a full calculation to know if such a setup does make sense or not.
considering additional weight, you might increase the mileage NOT charging the batteries on the road *shrugs*
IDK.. things like that are a bit tricky to calculate thus blurry to imagine right...
but it's on you to do that properly (your school project, not mine )

'sid