[svsantosh]

Currently my CJ340 Jeep has the stock spec alternator - 35Amp/Hr (IIRC). I have a 70Ah battery, which means, from DEAD condition (hypothetically), the Amp needs about 2 hours to charge the battery to full.

Addition to above see (Off-Roading Lights) this calculation. I have similar powered bulbs currently installed in my jeep. Roughly 40Amps, which is over my Alternator capacity, and will start draining my battery. I am not even bringing a Electrical-Winch into a picture here. Thats a completely different requirement.

Now, my questions are:

1) Can we 'open & modify' to increase the output of the stock 'Alt' from 35A to say 45A or 50A? Is it even remotely possible? Engineers please comment, can a spec-1 motor can be rewound/altered to give a spec-2 (higher) output?

2) My electrician said something about the 'Tata 407' alternator (or likewise) being made to fit in a jeep and power the electricals. Is it feasible? "Sensible?" What is the output of the T-407's Alt? At 1500Rs for a readily available 2nd hand unit, this sounds affordable.

3) Have seen a few fit a Tata Safari's 135~A/Hr Alt (IIRC) into their 5X0's. Is it expensive? Advisable?

4) What is a difference from a 35A Alt and say' a 55A alt (considering they are of the same genre - The old dynamo type and not the newer vacuum, etc etc). Does a higher rating mean MORE LOAD on the engine? What are the key differentiators?

This thread can be reffered by all those who are running extra lights and not sure about their current Alternator & Battery combo...

Something to read while at this. Alternators

[Sudarshan]

In any case DO NOT buy a second hand alternator ( or any item such as starter motor , wiper motor etc ) just to save 3/4 ks . That should be THE 'last' option. ( where you have an odd model like I have )

Forget reliability of 'such ' second hand items ( think, why they are in the second hand market ).

Upgrading with a new piece is quite a worth of your hard earned money .

Sudarshan

[Aroy]

Originally Posted by svsantosh

1) Can we 'open & modify' to increase the output of the stock 'Alt' from 35A to say 45A or 50A? Is it even remotely possible? Engineers please comment, can a spec-1 motor can be rewound/altered to give a spec-2 (higher) output?

1. Normally NO. You can increase the power by using a smaller pulley, so that it runs faster, but then the excess current will burn the coils, and the bearings will give up.

Originally Posted by svsantosh

2) My electrician said something about the 'Tata 407' alternator (or likewise) being made to fit in a jeep and power the electricals. Is it feasible? "Sensible?" What is the output of the T-407's Alt? At 1500Rs for a readily available 2nd hand unit, this sounds affordable.

2. YES you can try putting higher power alternator. Be sure that the alternator speed matches its specifications, too low and it will not produce sufficient voltage at idling, too high and it may burn out.

Originally Posted by svsantosh

3) Have seen a few fit a Tata Safari's 135~A/Hr Alt (IIRC) into their 5X0's. Is it expensive? Advisable?

3. No idea of the costs. Should be easily verified from a spare parts shop.

Originally Posted by svsantosh

4) What is a difference from a 35A Alt and say' a 55A alt (considering they are of the same genre - The old dynamo type and not the newer vacuum, etc etc). Does a higher rating mean MORE LOAD on the engine? What are the key differentiators?

4. Older vehicles had a "Dynamo", that is a DC device. Newer generation have an "Alternator", that is an AC device. In a dynamo there is a commutator. The brushes pick up current from a ribbed surface which wears the brushes fast, hence you normally did not run the dynamo at high speed which would result in abnormal wear resulting in frequent replacement of brushes. An alternator has either no brushes, or brushes on smooth rings, hence they can be run at higher speed with very little wear. Plus there is a rectifier to change AC to DC. Increasing power requires increasing the rectifier rating also.

The alternator will load your engine (power has to come from somewhere!)
The load in HP is easily - calculated E=I*V, where E=power in watts, I=current in amps and V=voltage (12V nominal). Hence a 100A alternator will consume 1200W nominal or about 1.5KW taking into account losses in the system. This is about 2HP.

[svsantosh]

Realized during my rebuild that the alternator that has worked for nearly 2 years on my jeep is not OE and belongs to the TATA 407's...!!



Learnt that it comes 60Ah rated from the manufacturer, so it is neary twice better than the OE 35Ah (?) from M&M. It has worked without a glitch for last 2 years, not once it has failed to charge the battery correctly. Got it completely overhauled today and had to change a few regular parts for its continued efficiency.



So, If anyone wants a better Alternator in their Jeep (Over the OE) this may be a good idea. PS - Also learnt the Sumo's AMP is a 65Ah one and would do the same good job.

Remember, these alternators are the NON-VACUUM types... will not work on the jeeps with Booster brakes.

[Sutripta]

Originally Posted by Aroy

1. Normally NO. You can increase the power by using a smaller pulley, so that it runs faster, but then the excess current will burn the coils

Hi,
Could you please explain?

Regards
Sutripta

[Jaggu]

Originally Posted by Sutripta

Hi,
Could you please explain?

Regards
Sutripta

Yup even i did not get that point, i thought alternators are different from dynamo's in this aspect?

[lugnut]

A question here -

Do the RPMs of the alternator and the engine need to be in sync, irrespective of the ampere-hour rating?

Thanks.

[ex670c]

Originally Posted by svsantosh

Currently my CJ340 Jeep has the stock spec alternator - 35Amp/Hr (IIRC). I have a 70Ah battery, which means, from DEAD condition (hypothetically), the Amp needs about 2 hours to charge the battery to full.

Addition to above see (Off-Roading Lights) this calculation. I have similar powered bulbs currently installed in my jeep. Roughly 40Amps, which is over my Alternator capacity, and will start draining my battery. I am not even bringing a Electrical-Winch into a picture here. Thats a completely different requirement.

Now, my questions are:

1) Can we 'open & modify' to increase the output of the stock 'Alt' from 35A to say 45A or 50A? Is it even remotely possible? Engineers please comment, can a spec-1 motor can be rewound/altered to give a spec-2 (higher) output?

2) My electrician said something about the 'Tata 407' alternator (or likewise) being made to fit in a jeep and power the electricals. Is it feasible? "Sensible?" What is the output of the T-407's Alt? At 1500Rs for a readily available 2nd hand unit, this sounds affordable.

3) Have seen a few fit a Tata Safari's 135~A/Hr Alt (IIRC) into their 5X0's. Is it expensive? Advisable?

4) What is a difference from a 35A Alt and say' a 55A alt (considering they are of the same genre - The old dynamo type and not the newer vacuum, etc etc). Does a higher rating mean MORE LOAD on the engine? What are the key differentiators?

This thread can be reffered by all those who are running extra lights and not sure about their current Alternator & Battery combo...

Something to read while at this. Alternators

Originally Posted by Sudarshan

In any case DO NOT buy a second hand alternator ( or any item such as starter motor , wiper motor etc ) just to save 3/4 ks . That should be THE 'last' option. ( where you have an odd model like I have )

Forget reliability of 'such ' second hand items ( think, why they are in the second hand market ).

Upgrading with a new piece is quite a worth of your hard earned money .

Sudarshan

Hi SVS,

Service your stock alternator, check the rectifier and while installing connect a 6mm wire from the Alternator + Output to the Battery + Terminal.

The Normal Route is via the Starter Solenoid, but if the starter is wet then it will draw a small current.
DB Sir has made an exhaustive post on this in an electrical thread.

@ SudarshanJEE,

There is no harm in buying second hand Alternator & Starter Motors, actually they are very cost effective.

However the person buying should understand the functioning and the cost of basic repairs.

New Alternator - 5-10K
Second hand serviced - 1-4K + Rs 1500 for Servicing with Lucas-TVS/Bosch parts.

New Starter Motor 9 K upwards.
Second Hand Rs1-2K + Rs1500 for a comprehensive rebuild.

My rebuild usually last perfectly till the next time I dunk them in water. So I have 2 Alternator and Starter Motors for my 4x4 Vehicles.

Regards,

Arka

[svsantosh]

Hi Arka,

Actually you 1st made me scratch my head - all batteries have a +ve wire connected to the starter motor, and the -ve connected to the body for earth... Where does the 'charge' to the battery come from the alternator??

Now I realized that the starter motor acts as some interface, I need to research this further, also can you post the link of DB's comments on linking the +ve of alt & battery - sounds that should be the right way of charging the battery!!

Also, learnt my starter motor (at least the body) is a 1984 manufactured one, so clearly it is a used/gujri one since my jeep is a 1990 model.

[Aroy]

Originally Posted by Sutripta

Hi,
Could you please explain?

Regards
Sutripta

Let me try.

Each generator (and alternator is a generator), generates Voltage proportional to its speed of rotation. Automotive alternators are designed to generate voltage slightly more than battery voltage at normal idling speed of the vehicle, so that there is a net power flow from alternator to the vehicle electrical requirements. In contrast older generation of vehicles had a Dynamo (a DC generator), which would generate battery voltage only at higher RPM. This is due to the fact that dynamos had commutators which would wear the brushes very fast at high rpm, so they were designed for use at lower (generator) rpm.

As the engine speed increases, the voltage and there fore the current increases. So in effect if an alternator is rated at 60A at 3000 engine rpm, it will deliver less at idling and more at say 4000 rpm. The regulator electronics in the alternator does two jobs
1. Transform AC to DC
2. Regulates the voltage, so that excess current is not drawn from the alternator at high speed, burning it.

In order to get more current from an alternator you have to
1. Run it at higher speed. This is achieved by using a smaller pulley in the alternator. As the linear velocity of the belt is same (at a given engine rpm), a smaller pulley will revolve faster. This will give more current at lower speeds, especially at idling.

2. Modify the regulator electronics, so that it allows higher current to be generated at higher RPM

3. Cool the alternator, as extra current drawn will over heat it. Thus extra cooling fans will be needed.

As sleeve bearings will give way at high speed, the alternator will now require ball or roller bearings at each end of the shaft.

[svsantosh]

The TATA 407 alternator in the above pics came with 2 roller bearings which were practically dry and needed re-greasing - promptly done and sounds much better now.

[Sutripta]

Originally Posted by Aroy

Let me try.
......

Lots of questions and comments, but let me pick and choose.

A) What effect will just fitting a smaller pulley have, esp. with regard to max current output/ burning out?

B) Why do dynamo systems have an active current limiting system, and not alternator systems?

C) If one dead shorts the output of an alternator (if one is pedantic, add that field is supplied from separate 12V supply), what will be the rpm - current graph?

Regards
Sutripta

[Sudarshan]

Originally Posted by ex670c

@ SudarshanJEE,

Jee Sirji , please let me clear my name

There is no harm in buying second hand Alternator & Starter Motors, actually they are very cost effective.

Not against repairs -- my advice was wrt replacements ,( when the part is beyond repair & one is in need to change it )

My rebuild usually last perfectly till the next time I dunk them in water. So I have 2 Alternator and Starter Motors for my 4x4 Vehicles.

Regards,

Arka

Arkaji - everyone is not like you or me -- for you & me alternator/Starter is a few bolts & wires job which takes 15/ 20 minutes to take out or fit in .I also tend to keep few things in hand , but not everyone here can or will or is willing to turn his house in a parts godown --

Many here don't seem to be DIY people ---So I tend to give safest advice to people so they will have peace of mind & enjoy their Jeep more than spending time at mechs .

So thats the reason why I said that , may be this is little costly but a guaranteed way

Again I am not against old/secondhand parts , ( I have this Odd vehicle for which nothing is available off the shelf ) I my self do many things as trial & error but not everyone can do it , I have to those things to keep my machine working --- but cant advice people to do the same -- especially when they depend on a mechanic

Sudarshan

[Aroy]

Originally Posted by Sutripta

Lots of questions and comments, but let me pick and choose.

A) What effect will just fitting a smaller pulley have, esp. with regard to max current output/ burning out?

B) Why do dynamo systems have an active current limiting system, and not alternator systems?

C) If one dead shorts the output of an alternator (if one is pedantic, add that field is supplied from separate 12V supply), what will be the rpm - current graph?

Regards
Sutripta

Before answering your queries, here are some good articles on Alternators, which between them explain most of the queries regarding alternator theory, repair and sizing.

Alternators
Alternator Repair
Alternator cooling fan

A. A smaller pulley will speed up the alternator. This will result in higher current at lower engine RPM. Similarly there will be higher than designed current at higher engine RPM. If the current is high enough and cooling not sufficient then the alternator will over heat and finally can burn out. Please note it is not the alternator winding, but the insulation which burns. As such copper coils can easily be heated to 150 degrees or more without any electrical degradation. The diodes may also blow if current is beyond their rating (they will overheat and then blow).

B. Dynamos are the simplest of electrical generators. There is the field coil and the rotating coil. As alternators have diodes for converting AC to DC, it is very easy to incorporate current limiting circuit at a nominal cost. In contrast dynamos have no rectifiers, so putting a current limiting device is an extra expense. That is why the voltage regulator, current limiter and dynamo cut-out are housed in a separate box.

C. The current limiting is not fool proof, and though I have never faced it, I think that a dead short on the alternator out put will
. Draw excess current
. The excess current will blow the rectifiers. Depending on your luck the rectifiers will either be shorted (most likely) or be open (like a fuse!). Only once in my M800 the rectifier shorted out when it had traversed through deep water for quite some time (water must have seeped into the alternator), other wise the alternators in all my cars have behaved till date. I have read that there are water proof alternator available through specialists for extreme off roading situation - prolonged wading and river crossings.

Why Alternators can run faster, hence charge at idling.
As the field direction keeps changing, in a dynamo a commutator (direction changer!) is used to maintain the current in one direction only (DC current). It is the commutator which is the bane of high speed dynamo. As the commutator has segmented construction, the brushes get abraded at the discontinuities. The abrasion rate accelerates with rotational velocity, so that beyond a speed the commutator acts as grinding wheel and literally eats up the brushes in no time. As the alternator has no commutator, but a slip ring the brushes are not abraded easily, hence an alternator can run much faster than a dynamo. To charge at idling the alternator is designed to run fast enough to charge at low RPM of the engine ~ 1000 RPM. As there is no commutator it can easily run at 6000-8000 RPM without problems, provided the bearings can take it.

For higher reliability Brushless Alternators are also available and have a long life - 200-500K km, coupled with sealed bearings they will out last the life of the commercial vehicle without any attention.

[Sutripta]

Originally Posted by Aroy

Before answering your queries, here are some good articles on Alternators, which between them explain most of the queries regarding alternator theory, repair and sizing.

Went through them. Thanks. Too elementary, and not really relevant to our discussion.

A. A smaller pulley will speed up the alternator. This will result in higher current at lower engine RPM. Similarly there will be higher than designed current at higher engine RPM.

Is the alternator a voltage source or a current source?

If the current is high enough and cooling not sufficient then the alternator will over heat and finally can burn out.

Agreed. But the question is will the current exceed limits on fitting a smaller pulley.

Please note it is not the alternator winding, but the insulation which burns. As such copper coils can easily be heated to 150 degrees or more without any electrical degradation.

Yes. B, F, H. Relevance to our discussion?

The diodes may also blow if current is beyond their rating (they will overheat and then blow).

Also yes. Also see third comment.

B. Dynamos are the simplest of electrical generators. There is the field coil and the rotating coil. As alternators have diodes for converting AC to DC, it is very easy to incorporate current limiting circuit at a nominal cost. In contrast dynamos have no rectifiers, so putting a current limiting device is an extra expense. That is why the voltage regulator, current limiter and dynamo cut-out are housed in a separate box.

The rectifiers have any role in regulation?
In any case, the question was why alternators do not have current limiters like dynamos. Where it is placed is not relevant.

C. The current limiting is not fool proof, and though I have never faced it, I think that a dead short on the alternator out put will
. Draw excess current

What current limiting?
Check out the current vs rpm graph in one of your links.

Why Alternators can run faster, hence charge at idling.
As the field direction keeps changing, in a dynamo a commutator (direction changer!) is used to maintain the current in one direction only (DC current). It is the commutator which is the bane of high speed dynamo. As the commutator has segmented construction, the brushes get abraded at the discontinuities. The abrasion rate accelerates with rotational velocity, so that beyond a speed the commutator acts as grinding wheel and literally eats up the brushes in no time. As the alternator has no commutator, but a slip ring the brushes are not abraded easily, hence an alternator can run much faster than a dynamo. To charge at idling the alternator is designed to run fast enough to charge at low RPM of the engine ~ 1000 RPM. As there is no commutator it can easily run at 6000-8000 RPM without problems, provided the bearings can take it.

For higher reliability Brushless Alternators are also available and have a long life - 200-500K km, coupled with sealed bearings they will out last the life of the commercial vehicle without any attention.

Totally irrelevant to our discussion, I would think.

Remember, our discussion started with this

1. Normally NO. You can increase the power by using a smaller pulley, so that it runs faster, but then the excess current will burn the coils

Regards
Sutripta