Portable Altenator

Hi Lionel

The motor would be too small.

You need about 2.5Hp to run a 50A Alternator, anything smaller it would stall.

Regards

Derek.

Thought along those lines also Lionel.

There is a small 22AMP alternator and it would go well with a small petrol engine.

To me there is a complete lack of a small easily used means of recharging you batteries , most of the 12 v generators have come out big and heavy or noisy.

The closest to the perfect product was a now extinct 2 strke honda 300 generator which weighed less at 7kg than anythong you can now buy.
It could have put out 20 amps but only did 6 for cost reasons, still looking for one of these , in the meantime I just use a small lithium cell pack.

Just a wee sum here, Alternator 50amp x 12v = 600w, 1hp = 746w,

I believe the little engine would need to be 1HP or better to deliver the full 50amps.

What's the HP of a whipper moter at full Revs??

piddlefimp

Lionel, yes, 2.5 HP Honda 4 stroke motor, same as the commercial alternator available, married to a 55 amp alt, external "taxi" regulator, a link can be fitted with a switch, 12.8 volts or 16 volts. Depends if your batteries can handle the increased voltage for a short time or not. Works for me.

All sorts of rigs (mostly pedal power) have been used in the past to charge batteries or power RFDS radios. Same during WW2. Smaller rigs were often pedalled by hand.

I'm sure Doug T could come with a history lesson for us on the subject.... (:
Hi Doug..!

as other have said -- motor is too small - if your looking for a small motor - try ebay - you can pick up one for about $150 I have seen the device you mention in some 4x4 magazines and they want about $700 for the item - and its just a reco alternator coupled to a Honda motor.

So they are on the market - but i am sure you could make one yourself if your handy on the tools

Boc

My son made one using a motor from a GMC genset. I don't know the size of the alternator

Hey Mate,

This is the engine I was thinking of for the same application. Honda Engines

Its got 2.1 hp. Check out these little beauties from down the bottom of the page: mini hondas

Matt

G'day mate - your idea has merits.

Sticking with your philosophy of doing it cheap and dirty....

Your engine is never too small for battery charging - just limit the current. The bike solution is an excellent example for this, as humans only churn out a couple 100 Watts (bit over a quarter of one HP) over time (not talking tour de france contenders here).

And this is what I'd do:
grab 15 metres of ordinary 2.5 mm square 240VAC building wire, the 20 amp stuff (or any #13 wire as long as it is copper) and wire it in series between your batt and the alternator.
This will effectively drop the max charge current through your 12V batt down to about 20A. At 50% 'alternator efficiency' your motor should see an initial load of about 0.65 HP. Note this load will decrease as the charging progresses and the current through the battery tapers off.
Make sure there is good ventilation around the wire as the maximum heat dissipation in the early charging stages will reach 40W.
Increase the length of the wire if you need to further limit the initial maximum load.

best of luck, mr.batteryvalue
wish I was an automotive engineer ;)