Replace alternator with higher amperage

[Chris]

That was pretty much my understanding Dr Gra. And at the point where the battery and alternator sort of level out, your winch won't be running anymore (under load) because the flattened battery and running alternator simply cannot power it. So wait a few mins and go again. Of course with a standard battery, deep discharging isn't recommended. So best to not get to the point where the winch IS stalling. I do like Rob and OGs points about upgrading the cable between the alternator output terminal and the battery. But not sure it's necessary. Maybe you can do the math. If a flattened battery pulls 60s amp, then it could do that from an 80 amp alternator now, so the cable should be ready for that, yes? I am not sure under what conditions my alternator would be supplying its max of 120 amp really. But I have three batteries and I do on occasions run the front and rear together.

I bought the higher capacity unit because I needed a new alternator and it was the same money. The bearings had gone in the recon unit I had on there. I didn't specificaly set out to upgrade.

Chris

 

[Nuclear Chicken]

Chris

Gra is spot on as he knows a lot about this stuff! The fact of the matter is that if you have a 80A alternator, 100A, 120A or whatever, the connection to the 'system' (in this case the battery) must be capable of handing the current the alternator can produce. Simples. Other than that all other wiring should be fine as, has been pointed out, there's no difference to any connected load so 'consumed' current won't change. If, as per the very first question, it's just a swap of alternator for convenience, there's probably no need to change anything as the consumed load in the car is the same, even though the alternator can produce a bit more, which is of little relevance.

 

[Chris]

He knows a lot about a lot actually. But it's not me that's confused. Although I am still considering the cable upgrade. If I have been double winching, front and rear batteries could be charging. Now, not sure, but I think my new split charge won't allow power to the rear until my front battery is pretty much topped up. So it may not be possible to charge them heavily, both at once. But I can force connect them from the control panel.

I can tell you one thing. Man it's quieter and smoother with the new alternator on. Just need to drop some new bearings into the old one to have on stand by.

Chris

 

[AlternatorMan]

Your alternator doesn't really 'recharge' the battery, as much as it produces satisfactory current to prevent the battery from discharging. The only time you should draw current from the battery is on vehicle start-up, or when you draw more power than the alternator can produce. The alternator isn't designed to recharge a flat battery, either. Doing so will burn up your bridge rectifier.

For efficiency, upgrade the wires going from the alternator to the battery, using wires rated 50% above your alternator output. You don't have to change out any accessory wires, unless you plan on upgrading said accessories. It's also a good idea to run a ground wire directly from your alternator case to the battery negative.

You see, the vehicle ground sinks directly at the alternator, not the battery. Any generated current has to travel through your alternator bracket, engine block, and chassis ground connections, which is fine when the connections are shiny and new. But as time creeps into these mating surfaces, they build up a resistance. This resistance leads to excess heat in your alternator and battery cables, leading to problems like burnt up diodes and internal wire corrosion. Running the connection directly from the alternator case to your battery will give your alternator a much longer life.

 

[Chris]

Well, isn't that interesting. I am all over that. Extra earth on its way. I actually have put in extra earths here and there already for one reason or another. But this is a new one. I have looked at the alternator supply cable today and it pretty big. I couldn't remember so I went and looked. Not sure it needs upgrading really. It's not exactly a piece of string. I suppose there is nothing to stop me adding a second one from there straight to the battery terminal is there?

Welcome aboard AlternatorMan. Now it's purely a guess from your name but .........

Chris

 

[Chris]

Hey good website. I have just answered my own questions AlternatorMan.

Cool stuff

Chris

 

[Rob]

I do not see a problem running another cable from your alternator to your battery Chris, better to be on the safe side than for your cruiser to burn out again. Since Great White went up in smoke and various test rig fires at work I am really careful to select the correct sized wires for the application. That is either use a correctly sized fuse for the cable and/or use cabling that will easily handle the current of whatever is connected can draw/produce. So if you have a 120A alternator and your vehicle wiring was designed with the 80 amp alternator in mind then I would recommend upgrading the cable from the alternator to the battery just to be on the safe side regardless whether you can figure out if you can or can't draw 120A.

Another way to look at it, say you have a 20A DC power supply and are testing a 2A motor and the motor shorts you then could draw 20A and cause a fire if you do not use adequate cabling or an appropriately sized fuse. OK no battery but the principle is the same use 20A cabling or a 3A fuse.

 

[Chris]

I'm not so worried about that really Rob. The fire in GW was not really one that stemmed from a wiring fault. It was a component failure. Anyway, I have looked on AM's website and I can piggy back a new cable, via a fuse which is sensible. But I say again the OEM one is not a small cable. However, it doesn't go straight to the main battery. It disappears off toward the 2nd battery and the change over relay area. It was dark so I couldn't track it fully. Why would it go off over there?

Chris

 

[sae70]

I conquer Chris, a great website and very interesting

I'm loving the concept of a 350Amp 12v alternator with a remote bridge, very cool I'm guessing that having a remote bridge removes a lot of the heat from the alternator when running under high loads. I have read in the past about 400+Amp water cooled alternators on heavy plant

How on earth did you stumble over us having this alternator debate then AlternatorMan

 

[Chris]

AlternatorMan is omnipresent and knows all Steve.

All we do is shine the big alternator symbol in the sky and he shall appear.

Yep, that should do it.


Any time around now.

He's a comin'.

 

[AlternatorMan]

...the OEM one is not a small cable. However, it doesn't go straight to the main battery. It disappears off toward the 2nd battery and the change over relay area. It was dark so I couldn't track it fully. Why would it go off over there?

Chris

Those weird wiring detours from the factory are why I recommend piggy-backing new wire in, rather than replace the old cables.

How on earth did you stumble over us having this alternator debate then AlternatorMan

I get a lot of email questions. Most of them are from forum-goers, and forums like this have helped me out a lot. So I decided, why not give back and answer questions directly on the forums?

 

[Rob]

Those weird wiring detours from the factory are why I recommend piggy-backing new wire in, rather than replace the old cables.

The issue on the diesel 80 is that the changeover relay changes the batteries from 12v configuration to 24v during startup so I do not think it will be that simple. May have to follow the existing route Chris and piggy back the 2 positive cables from the relay to the batteries.

 

[Chris]

What if I simply piggy back a new cable from the alternator to the split charge relay? The only time I'll really be pulling a bigger load than standard is when I am charging my rear battery. As this is connected to the main battery, it will be a route to that too and I guess the aux battery.

I shall have a look today in the sunshine. Just not sure why it goes where it does Rob. It probably goes off the a terminal on the relay then is split back again to the two batteries.I don't think that the charge comes via the second battery terminal.

Chris

 

[OG.]

.
Hi OG,

Sorry but you are quite wrong with your explanation that your battery will never draw more than 25 amps or so.
Who told you that, or how did you come to that conclusion?

If your battery was flat, like just 10 volts at open circuit terminal voltage, then the internal resistance with a pb battery will be very low.
I can work it out, but bore you to death
The lower the internal resistance of the battery, then allows the alternator voltage to rise, past it's general charge voltage of 14,7.
When the alternator feeds into a pb battery with low internal resistance, the battery will try to pull the alternator volts down, as it pulls the alternator voltage down, the amps rise proportionately until stability is met.

You could quite easily have 60 amps or more feeding into a flat battery, because I = V over R
Having a larger alternator gives you the ability to refill the discharging battery (via winching) however, as the amps are being used up out of the battery, the alternator is replenishing them also.
So a larger capacity alternator will replenish the used "winching amps" and at a point, when the amps are flowing out of the battery faster than the alternator can resupply them, then the alternator becomes the winches primary power supply.

Gra.

I have to disagree.
When charging the on charge voltage of the battery opposes the charging voltage which of course must be higher than the battery voltage or charging stops. The battery will also be partially sulphated. Sulphate is an insulator so plate area is reduced. The electrolyte has also become less concentrated as the specific gravity drops reducing its conductivity and this increases resistance to 0.02 ohm or more though none of the respected authorities on batteries will quote a figure. When charged the resistance will be less than 1/10 of this figure, so doing ohms law calculations is always a bit misleading

A battery is 100% discharged on load at 10.8v and going lower than this causes difficult to remove sulphation. When on charge the battery voltage rapidly rises to 12.5v and more. A good but discharged battery will show over 12.5v with no load . At 10v open circuit it will be nearly dead. A battery should never be discharged to 10v or it will suffer irreversible damage.

An alternator does not jump immediately to 14.7v when running...its voltage is held down to just above battery voltage and only when charge current drops is it able to reach 14.4v Its rated output is for the supply of resistive loads not battery charging..

so if you fit a 100A alternator it will not charge the battery at 100A ..if it did it would overheat fast and gas and bubble acid all over the place ..BUT it will supply 100A to your winch or lights or HRW etc.

 

[Chris]

Well it appears that the cable from the alternator goes across the top of the rad and straight onto the aux battery terminal. It then dives off to the B Battery terminal junction box next to the change over relay. It splits then and the part that doesn't go to the starter motor, joins up with the 24v change over relay. From there is goes back across the rad onto the main battery terminal. This section is much thicker than than the original from the alternator. So if anything does need thickening up it's not this final section. It's a very circuitous route to take. There has to be a reason for this, but I am not sure what it is. I am not clever, or brave enough to connect a second cable from the alternator directly to the main battery +ve post. Although that would be the obvious thing in my mind. That is where the winch is attached and would be pulling from directly.

Chris

 

[Rob]

Are you saying that on your 80 the alternator is connected directly to the aux battery? That can't be right as the aux battery gets switched from parallel to series to give to 24v.

 

[Chris]

I know Rob. As mad as it seems. The alternator cable does NOT go straight to the main battery. Well, hey maybe I have the wrong battery. I view the driver's side battery as the main one and the passenger side, the one next to the washer bottle as the aux.

I don't pretend to understand. I just live here.

Chris

 

[Rob]

Well at least we know we are talking about the same batteries. I will have a look under the bonnet the next time there is daylight and I am at home which will probably be the weekend.

 

[Chris]

What I haven't tested is which terminals it's connected to on the change over relay. Looking at it logically, I'd have to presume that they're both permanently live terminals.

Chris

 

[Jon Wildsmith]

the drivers side battery connects to the terminal on the drivers side of the change over relay. That is normally connected to the terminal nearest the passenger side battery which has a fly lead to the B+ connection box which then has a wire to the starter and the +ve terminal of the passenger side battery. The passenger side terminal on the change over is connected to the passenger side battery -ve and is normally connected to the terminal farthest from the batteries that has a cable going to the engine block. So normally both batteries are in parallel. During 24v starting, the drivers side terminal (that the drivers side +ve is connected to) is instead connected to the passenger side terminal (passenger side battery -ve) so the +ve terminal of the passenger battery and the B+ connector and feed to the starter are at 24v. If you had an extra wire from the alternator to the +ve of the drivers side battery then during 24v starting it would short circuit the passenger side battery terminals which probably wouldn't be a good thing

Can't answer the why did they do that question really, I can only guess it's something to do with inhibiting alternator power drain during starting?