gas engine and alternator

hello all,

I have a large 150 pound robot with a 35 amp am hour lead acid battery. This robot has a lot of space in it and the battery runs out quickly. I don't want to put more batteries because of the weight it would add but I am looking for other ideas to power the robot. I was hoping to generate at most 5 amps at 12 volts to power electronics and motors and to charge the battery. I was thinking of a small gas engine with alternator and charger circuit. Of course this would only be used outside. and if i went with a gas engine i would need a way for the robot to start and stop it with out human intervention

Thanks Guys!

How about lighter battery packs? LiPo, LiIOn, LiFe, some kind of lithium cell? The kind they use in electric cars.

arduinoPi:
I was thinking of a small gas engine with alternator and charger circuit. Of course this would only be used outside. and if i went with a gas engine i would need a way for the robot to start and stop it with out human intervention

I don’t think that is a practical option unless {A}one of the off-the-shelf small gennys is suitable - my guess is it would be much too big and they generate AC rather than DC - or {B} you are prepared to buy a small motor, an alternator and build the rest yourself.

I have only come across one genny that drives a 12v alternator - all the rest (especially the cheap ones) generate mains voltage AC.

…R

What do electric golf carts use? They haul the cart, 2 golfers, and 2 sets of clubs around for 5+ hours on a single charge, up hills too.

Or gas carts - step on the peddle, the gas engine starts up an off you go.

Fuel cells exist that meet your spec exactly, fairly expensive though.

the robot also has a computer psu to accept ac so it would be possible to connect a generator to that. thank you guys for the comments

Here's an auto start for an RC engine. Rather than looking for an alternator, you might look for a DC permanent magnet motor to use as a generator, they work both ways. http://www.amain.com/rc-cars/traxxas-ez-start-starting-system-tra4570/p17794

CrossRoads: What do electric golf carts use?

I have golf-cart batteries on my boat - 6v 220Ah (doubled to give 12v). The 6v battery is about the size of a car starter battery, or maybe a bit bigger. And HEAVY.

...R

So I think I would choose to get a small AC generator and run it through a high power computer PSU. I looked some up on amazon and found a 800 watt version that weighs around 35 pounds. I could probably fit it inside the bot but isn't there something that gives off maybe 200 watts and is smaller? Like even from a non robot stand point. a little 100-200 watt generator to power a laptop or something at a campsite that is able to be carried. I feel like a device like that had to be invented already.

Here is the one I found: http://www.amazon.com/PowerPro-56101-2-Stroke-Generator-1000-watt/dp/B00J261PGQ/ref=sr_1_1?s=lawn-garden&ie=UTF8&qid=1442344220&sr=1-1&keywords=backup+generator&refinements=p_n_feature_four_browse-bin%3A3619898011

it actually has 12 volts out and AC out. 35 pounds and a little over a square foot. Now how hot would something like this get? I could run the air intakes and outtakes out of the bot.

Rc engines have been used for smaller generators , a search should find them.

The thing is rc engines are aircooled and need high airspeed for cooling.

arduinoPi: . I feel like a device like that had to be invented already.

It has , the fuel cell i mentioned earlier starts at 80 w.

More often found on boats than caravans, solar cells are common.

Generators are disliked on campsites due to noise.

You say you require 5A to power the motors, power the electronics, and to charge the battery.

So what do you mean by " the battery runs out quickly"..??

By my estimation a 35Ah capacity batery should be lasting you around 7 hours at the present time.

So is the battery old and not taking a full charge or is it good but not being fully charged to begin with?

Other than that is the robot mobile or can you plug it in to mains power or similar?

Perhaps if you want the motor generator arrangement, a used auto alternator would give you plenty of capacity (80A ) with an electric start 4 stroke lawn mower engine for power.(3 - 4 hp)

What you need is a Delco starter/generator (12V @ ~30A). Basically just a big brush motor designed for both purposes, and you mentioned you wanted to be able to rig it up so the engine would start on its own.

They're old tech but still very common. Not cheap, unfortunately :(

I would love some more information on Fuel cells, and I say around 5 amps because the robot has extra things that run while idling ranging from a LCD screen to 10 watt LEDs. The drive motors each use 20 amps at 12 volts. The robot isn't driving non stop all the time, It sits around a lot of the time to scan the environment or interact with people. I would appreciate more information on fuel cells, From what I can tell they can be used indoors? This could be really useful.

arduinoPi: I would appreciate more information on fuel cells,

Google.

And check your bank account at the same time.

...R

Google on brunton hydrogen generator.

Tht will find the toy one whick gives about 10 watts.

You'd be better off moving the thing around on gas motor power than

gas motor ---> generator at perhaps 30-50% loss ---> battery ---> electric motor at perhaps 40-60% loss

But I think you are married to the two 12V 20A battery-eating motors and control code, yes?

Are there any good compressed air motors? They should do for limited time, run cooler, etc.