12 volt generator/welder & battery setup

Submitted: Monday, May 01, 2006 at 22:14
ThreadID: 33436 Views:12087 Replies:5 FollowUps:12
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I am currently searching for an ideal electircal setup for remote long stay camping.
I recently purchased a 95litre fridgemate fridge from evacool with the DB50 danfoss compressor, and am in the market for a dual battery setup to complement it, I do a lot of weekend camping and the dual battery setup should be fine for that, at the moment I'm thinking of purchasing 2 105 amp AGM batteries 1 for the tinnie (which has no alternator) & 1 for the dual battery setup.
Every year I spend 3 weeks camping in the one spot and may not start the car for 4 days or more besides launching a tinnie,the campground is mostly shaded so solar wouldnt be a great option.
I was thinking of building a 12 volt generator(/charger/welder) similar to a christie. I already have a 3.5hp 4 stroke stationary engine.
I also know that it is also possable to build an electric welder from this type of setup so my questions are:
1.What are the best brand AGM batteries for fast charging & what is the quickest current they can they be charged at & how much do they cost?.
2. Has anyone else built a charger/ welder & is it ideal to do so on a 3.5hp engine. 3. What is the highest amp alternator this engine could push in this situation I'm thinking it will at most be charging 2 105 amp batteries at 80% discharged?
4. Does anyone have any experience building a generator that would be switchable from welding to charging , i understand that the regulator would have to be bypassed for welding but not sure on the intricacies of the welding setup.

I intend to buy a remote bush block in the next couple of years and a compact unit that could recharge,weld, and run an inverter would be very useful onsite.
Any info would be appreciated, this is a project that i would like to complete over several months (but before next chrissy) so I have some time on my side.
cheers matt
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Reply By: Derek from Affordable Batteries & Radiators - Tuesday, May 02, 2006 at 07:03

Tuesday, May 02, 2006 at 07:03
Hi mjf

1) Most AGM's are the same just check the warranty back up from the supplier, the most popular size is the 100 a/h one 330x175x210h and they will accept a maximum of 27 amps per hour charge decreasing as the battery 'fills' up. +- $300.00 (Check you local supplier or ebay)

2) I would not try to build one of these myself. Generators have come down in price and are very quiet and reliable. I would buy a good quality charger as a alternator can't fully charge a battery if it has sulphation (Common in auxiliary batteries) and match a generator to a portable welder.

The whole set up will be lighter and more reliable and in the end may even be cheaper.

Regards Derek
AnswerID: 170167

Follow Up By: kesh - Tuesday, May 02, 2006 at 08:05

Tuesday, May 02, 2006 at 08:05
Matt. We have a remote work camp, often nearly 2 weeks between use of the vehicle. On board is a 60l. Trailblaza which is used purely as a freezer.
About 12 yrs. ago (when we bought the Trailblaza) I made up a battery charger using a 4.5hp. Honda engine v belt driving a Denso 12v. alternator. This is the old external regulator type and I use a Bosch re 55 electronic regulator for control.
Have both voltmeter and ammeter wired in and as the battery charge comes up I can regulate the engine speed down for economy. The unit puts out about 45a @ 14.8v. (depending on residual charge in battery) until the regulator starts to bring the current down. About 4-5l.petrol/wk. keeps all batteries fully charged. Runs about 1 - 1.5hrs./day.

There is no way this would double as a welder. I have a Lincoln welder/generator (5kva @240v./180a.) and even running a 12g. rod makes the 11hp. engine work. I think if you need to run a welder a 240v./3.5kva generator would be min. to power it or failing that there are good diesel units available on eBay.
kesh
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Reply By: Russel & Mary - Tuesday, May 02, 2006 at 08:58

Tuesday, May 02, 2006 at 08:58
years ago you could buy an alternator/welder and fit it to your vehicle. I haven't seen any advertising lately, anyone else ?. Rus.
AnswerID: 170178

Follow Up By: disco driver - Tuesday, May 02, 2006 at 18:05

Tuesday, May 02, 2006 at 18:05
Hi Rus,
Not that many years ago, but yes I can remember them too,
They were known as "Auto-Arc" and were a modified Bosch Alternator with some extra electronics added. Never owned one but used one belonging to mechanic mate to weld up broken spring mount on my old 1962 Series 2 L/Rover SWB.
He had it fitted to his Series 2A service van.
Try googling and who knows what you may turn up.

Probably not compatible with all the computers etc on the modern 4WD.

Disco
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Reply By: Eric Experience. - Tuesday, May 02, 2006 at 09:53

Tuesday, May 02, 2006 at 09:53
Matt
You have the same plan as many others before you. The basic facts go against you on the welding, an automotive alternator is about 25% efficient so that 3.5 hp = 2kw x 25 % = 500 watts not enough to weld with. A generator is about 50% efficient= 1kw still not enough. A permanent magnet motor used as a generator can be 80% efficient, still not enough for a stick welder but will just run a gasless mig. the best electric motor for the job is the Fisher and Paykel washing machine motor, there are plans for using it on the web. Eric.
AnswerID: 170186

Follow Up By: Mike Harding - Tuesday, May 02, 2006 at 18:16

Tuesday, May 02, 2006 at 18:16
>the best electric motor for the job is the Fisher and Paykel washing
>machine motor, there are plans for using it on the web. Eric.

Sounds fascinating, I love re-using stuff like that - any links Eric?
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Follow Up By: Eric Experience. - Wednesday, May 03, 2006 at 18:01

Wednesday, May 03, 2006 at 18:01
Mike.
WWW.ecoinn.co.nz
Eric
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Follow Up By: Gu_Patrol - Wednesday, May 03, 2006 at 18:23

Wednesday, May 03, 2006 at 18:23
How about using a 24volt alt and have it independently working from your vehicle.

I know guys that have welded from a 12 volt battery, 2 x 12 volt (24volt is better) you know the welding kit you buy that clamps onto your battery the battery won't last long, but enough for some welding to get you out of trouble
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Follow Up By: Eric Experience. - Wednesday, May 03, 2006 at 18:54

Wednesday, May 03, 2006 at 18:54
Gu.
The voltage is not the problem with welding it is the current, a 12volt alternator has thicker winding than a 24 volt so can handle the current better. If you run a 12volt unit at high revs without a regulator you can get about 400volts obviosly the diodes wont take the voltage so you end up with a lot of smoke but if you build a special reg that is set to about 30volts and you use suitable doides you can weld ok but you have to have a very good belt drive, a normal v belt will not last long. Eric.
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Follow Up By: Gu_Patrol - Wednesday, May 03, 2006 at 18:56

Wednesday, May 03, 2006 at 18:56
OK :-)
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Follow Up By: mjf191 - Wednesday, May 03, 2006 at 23:35

Wednesday, May 03, 2006 at 23:35
Thanks to all who offered advice much appreciated,
I think the welder option has hit the scrap heap, I'll still be building the charger though. For the moment I'm gauging my plans off the larger 3hp 80amp christie charger, since my engine is 3.5hp should be enough for 80-90 amp alternator.
I have some more questions
1. I have read on another forum that alternators can't fully charge a battery without a 3 stage regulator, is this true do I need to replace the normal internal regulator to get a full charge.
2. What would be the best voltage protection. Would a circuit breaker be suffice?
3. I already have a 0-20 volts gauge would it be best to have an Amp gauge also & how much would a gauge suitable for high amps cost? (I'm working to a budget)
4. How would be the best way to make charge output adjustable, a switch or revs?
Any info appreciated
cheers
Matt
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Follow Up By: MartyB - Thursday, May 04, 2006 at 08:42

Thursday, May 04, 2006 at 08:42
Matt,
A friend of mine has a similar setup. One problem he said with his is the analogue gauges for volts & amps. The motor vibrations cause the needles to vibrate making the gauges inaccurate. You would be a lot off fitting digital meters. Oatley electronics have a kit for a digital meter.
www.oatleyelectronics.com/kits/k212.html

from Marty.
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Follow Up By: Mike Harding - Thursday, May 04, 2006 at 10:42

Thursday, May 04, 2006 at 10:42
>I have read on another forum that alternators can't fully charge
>a battery without a 3 stage regulator, is this true

No. Providing the alternator can supply current at a loaded voltage of about 14.4V then the battery will, in time, reach full charge. Three (or more) stage chargers just use some electronics to charge the battery in the minimum possible time and they also may extend battery life by minimising overcharge and performing an equalisation process on the cells.

>do I need to replace the normal internal regulator to get a full
>charge.

I very much doubt it.

>What would be the best voltage protection. Would a circuit breaker
>be suffice?

Why do you want “voltage protection” and what do you mean by that? A circuit breaker will open if the current through it exceed a given threshold for a given time – I doubt one would be a lot of use in your case – an appropriate size fuse would be simpler and cheaper.

>I already have a 0-20 volts gauge would it be best to have an
>Amp gauge also

Always a useful tool in battery charging – I would put one in.

>& how much would a gauge suitable for high amps cost?

Jaycar do a 100A current shunt for $20 – part number QP5414 and you’ll need a moving coil meter for about $18 to go with it. If you don’t know how to make an ammeter from those two parts drop me an e-mail and I’ll help.

>How would be the best way to make charge output adjustable,
>a switch or revs?

Why do you want to do this? Won’t the regulator on the alternator take care of charge rate?

Someone else suggested digital meters – ho hum… a digital meter is good if you are looking for very accurate readings but it won’t show a trend or peaks because it integrates it’s input data. For your application I would prefer analogue meters (ie. moving needle type) but they do need to be kept away from vibration.

Mike Harding

mike_harding@fastmail.fm
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Follow Up By: Eric Experience. - Friday, May 05, 2006 at 22:49

Friday, May 05, 2006 at 22:49
Matt.
As mentioned above, the automotive alternator will only give you 500 watts from a 3.5 hp motor, so the amps will be 500/15 a bit over 30 amps. the company that sells a unit with a 55 amp alternator on a 3hp motor implies it can produce 55 amps but it can not, it will produce about 20 amps at max revs, you dont want to run a max revs or you will annoy everbody and wear out you motor. If you use an alternator that is to big for the motor the motor will simply stall under load. it is better to use a small alternator so the motor is not overloaded, a 40 amp unit is best and lighter. Eric.
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Reply By: Member - Phil G (SA) - Wednesday, May 03, 2006 at 22:50

Wednesday, May 03, 2006 at 22:50
Welding is usually easily achieved with either 2 or 3 batteries to give you 24 or 36 volts. I just take away my welding lead and mask from home along with the set of jumper leads and a bunch of welding rods. Have used them in anger a few years back - can do a lot of welding with a set of N70 batteries - and still start the vehicle without problems.
AnswerID: 170561

Follow Up By: Member - Ed. C.- Thursday, May 04, 2006 at 10:17

Thursday, May 04, 2006 at 10:17
Ditto....
I've had to do the odd bit of track-side welding, and IMO (and in my experience), 36v will give a smoother arc than 24v... This will no doubt depend on the electrodes used, but it appears that most of the commonly available ones are meant to be used at a MIN. of 45volts (open circuit), though they will work ok on 36v....
I definitely prefer to use 3 batteries (36v) if they are available...
And yes, as mentioned, one can do quite a bit of welding with surprisingly little effect on battery capacity...
Confucius say.....
"He who lie underneath automobile with tool in hand,
....Not necessarily mechanic!!"

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Reply By: Shaker - Friday, May 05, 2006 at 22:56

Friday, May 05, 2006 at 22:56
We had a cruising yacht for sale recently that had a welder/alternator fitted, I am fairly sure that it also may been an AC generator as well. If you like, i can check back through our records & give the details.
AnswerID: 171066

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