Replace alternator with higher amperage

[Rob]

Just to be sure, will I get any problems if I replace say an 80A alternator with a 100A alternator? Both are for the same car/engine but the higher power one comes factory fitted on higher spec models only. My understanding is that you can.

 

[Andrew Prince]

Can't see why it would cause any problems. Obviously the more powerful alternator will draw more power from the engine, so I guess you'll use more fuel but whether you'll ever notice this, who knows?

Cheers,

 

[Rob]

Thanks Andrew, got myself a used one from ebay for £11.98! (not for the 80 BTW)

 

[Andrew Prince]

You not getting enough current with the original alternator?
As long as the new one's regulator is ok, you should be fine - I guess you've checked it will fit ok
Worth a gamble at the price

Cheers,

 

[Rob]

The original one is not charging properly and this is the cheapest one I could find that fits. Will try and rebuild the old one and keep it as a spare.

 

[Graham]

Can't see why it would cause any problems. Obviously the more powerful alternator will draw more power from the engine, so I guess you'll use more fuel but whether you'll ever notice this, who knows?

Cheers,

Not quite 100% there Andrew,

All it means is the 100A alternator has higher ability than the 80A alternator to produce electricity.

When you are driving with all your lights on, you may consume around 30 amps, both alternators will consume the same power from the engine to generate this '30A'

Where the 80A alternator will run at 100% to develop 80A, the 100A alternator will only be developing 80% of its capability of 100A.

So in short, both alternators will consume the same power from the engine up to 80A.

Graham

 

[Andrew Prince]

Right you are, Graham, although not quite 100% - only if you assume both alternators have the same efficiency Which they won't!
But I agree with your point - the point I was trying to make, which I obviously didn't succeed with, is IF you are using the higher output alternator for higher current, it consumes more power.

Cheers,

 

[tokaido]

Hi,
very interesting topic. Guys, I've been told that there are very high risk if we replace oem alternator to higher amp such 70 amp to 90 amp. The current will overloaded and can burn the engine's wiring and other electrical parts. My foreman said if i wanna replace to the higher amp alternator, i should replace the battery too that support the alternator. Is this true? I'm lil bit confuse. Till today i have no guts to replace to the high amp alternator.

 

[Chris]

That isn't quite how electricity work. The alternator doesn't just blast out 120 amps all the time down every wire at 12v. Each electrical thingy essentially drawers what current it needs. When you have lots of things running, like a winch for example, your alternator can run out of puff. Having one with more capacity means that you can supply more charge back to your battery as and when it demands it. Most of the time your alternator isn't running at peak. Especially on a diesel. You're just about using it to power the radio and dashboard lights.

And that's about as much as I understand.

Chris

 

[Rob]

Hi,
very interesting topic. Guys, I've been told that there are very high risk if we replace oem alternator to higher amp such 70 amp to 90 amp. The current will overloaded and can burn the engine's wiring and other electrical parts.

If you wire in additional accessors to the original wiring then yes you will, what I would recommend to do is to run additional wires from the battery to an auxiliary fuse box and that power to your accessories from there. You may also want to consider replacing the wiring from the alternator to the battery for a thicker cable to ensure you do not burn out the cable during excessive loading.

I did this on my old Volvo and it worked fine, no more typing in the radio code every time the engine revs dropped so I assume it worked well. I did not change any of the wiring as all the other electicals were standard so there was no additional current demand.

 

[tokaido]

Thank you very much chris and rob for the explanation ...now i understand how the alternator works. What i just understand from your view... we can replace to the higher amp alternator but also necessary: must add auxiliary fuse box and use thicker cable to prevent wire burning. Am i right?

 

[Rob]

As I said, it depends if you add any additional electrics. Let us know what additional loads you will be putting on the system if any and we will be able to give you more accurate advice.

 

[Chris]

OK so here is a really simple explanation. No you do not have to do anything with your wires.

OK, pretend I own a coal delivery business. I have a street with 30 houses. They all burn one bag of coal per day. I have a lorry that carries 30 bags. Great. Each day I deliver 30 bags, everyone's happy and I come home empty. One day, I buy a bigger lorry. I now can carry 40 bags of coal, but every day I come home with 10 bags still on. No one needs them. Shortly after that, some new houses are built. 10 of them. And they all want a bag each every day. Well fancy that. I have that capacity. 10 spare bags. I can supply that and we're all happy. No one needed to build a bigger fire place, I didn't need bigger bags, the coal didn't burn any hotter. Every house got what it needed.

Now if someone builds some more houses, I will need a bigger lorry!

Does that make sense? In short, who ever is telling you about needing bigger wires is talking complete bollocks. Mrs Smith at number 11 doesn't care what Mr Crabtree at 29 puts on his fire. But if he's cold and wants another bag on Tuesday, he can have one - it doesn't affect anyone else. UNLESS I only have a small lorry and can't carry enough coal for everyone. So, you stick a bigger alternator on, IF you have times when you want a bit more power because of high demand. Let's say winching or running something extra like a compressor. It makes no difference to the other things running on your car.

Chris

 

[Rob]

Chris, say you double the current capacity of the alternator and have a winch wired directly to your battery hopefully via a fuse or a kill switch of some sort and use adequate wiring, you will probably need to upgrade the wire that goes from the alternator to the battery. So taking your coal business analogy further, say you have a single track driveway to your coal depot and you are now delivering coal to an entire town you may want to expand the single track driveway to fit 2 lorries side by side.

Also if you attach say a winch to your cigarette lighter socket and fit a 200 amp fuse (impossible, but please do not do this) you will burn out the wiring. So if you do add a considerable amount of additional electrics to your vehicle don't piggy back of the existing wiring but use adequate wiring from the battery via a fuse. If all you are running is a satnav then you have nothing to worry about, you do not need additional wiring or a larger alternator or an additional fuse box.

 

[Chris]

I don't think so Rob. The winch isn't running from the alternator. It runs from the battery. The alternator is replenishing the battery not the winch. Even with a 120 amp alt I couldn't hope to touch the winch which is dragging something like 400 amps IIRC. Essentially all I am am doing is stretching out the point at which the winch stops. It's like filling a barrel with a hole in it. If the hole in the barrel is the same as the tap filling it, the level in the barrel never drops. If the hole is bigger then the barrel level drops by the difference between the hole and the tap. With no alternator at all (ie the engine is off) then you just flatten the battery. If the engine is running then you are adding charge but not as fast as you are emptying it.

The big current is running down the winch wire. Not down the alternator wire. OK so I have a bigger alternator, I'd figure the current charging system can cope with that. But the headlights, radio, interior light, fag lighter wires do NOT need upgrading do they. You winch for generally short periods at a time so things catch up. OK if I utterly flattened the main battery would the alternator then ramp up and replace that as fast as it could? Yes maybe it would. But that wasn't the question. The question was, if I simply fit a bigger alternator do I have to upgrade all my wiring? Answer no. Please let's not make it more complicated than that. a bigger capacity alternator does not put out a billion volts at a gillion amps and fry your electrics.

Chris

 

[OG.]

A battery will never draw more than 25A or so. Even totally flat that's the max it will deliver. Given there is a winch when the winch is operating the alternator will hit maximum output so the wiring between the alternator and the battery (or winch feed) will need upgrading to cope with the maximum output of the alternator. There is no need to upgrade any other wiring.

 

[Chris Green90]

Please forgive me if this sounds dumb but I think it may be right.

Although the battery is a "resovoir" for the current flow your winch is still connected directly to your alternator is it not (Weather through a fuse/kill switch etc.) so as soon as winching commences you start drawing extra current from the alt. This is proven (I think) in my truck as the alt belt is a little slack and starts to squeal when I winch for more that about 20 seconds. OK so the 400 amps is running down the winch wire but the alt will still be running at full capacity won't it?

I cant remember what I upped mine from and to (Think it was 90 to 120 amps) but it has been like that for about 2 years now and all seems fine and dandy.

 

[Chris]

OG, is that NEEDS upgrading or would BENEFIT from upgrading? What's to say that my current cable to the battery from the alternator isn't capable of handling the current, current? it would be dead easy to do but do I need to? If it only draws 25A then why upgrade? If the draw is limited then what difference does a 120 amp unit make over amp 80 amp unit? IN theory don't I only need a 25 amp alternator then? I get normal wiring stuff, but I do get a bit lost on alternators at times.

C

 

[Graham]

OK so here is a really simple explanation. No you do not have to do anything with your wires.

OK, pretend I own a coal delivery business. I have a street with 30 houses. They all burn one bag of coal per day. I have a lorry that carries 30 bags. Great. Each day I deliver 30 bags, everyone's happy and I come home empty. One day, I buy a bigger lorry. I now can carry 40 bags of coal, but every day I come home with 10 bags still on. No one needs them. Shortly after that, some new houses are built. 10 of them. And they all want a bag each every day. Well fancy that. I have that capacity. 10 spare bags. I can supply that and we're all happy. No one needed to build a bigger fire place, I didn't need bigger bags, the coal didn't burn any hotter. Every house got what it needed.

Now if someone builds some more houses, I will need a bigger lorry!

Does that make sense? In short, who ever is telling you about needing bigger wires is talking complete bollocks. Mrs Smith at number 11 doesn't care what Mr Crabtree at 29 puts on his fire. But if he's cold and wants another bag on Tuesday, he can have one - it doesn't affect anyone else. UNLESS I only have a small lorry and can't carry enough coal for everyone. So, you stick a bigger alternator on, IF you have times when you want a bit more power because of high demand. Let's say winching or running something extra like a compressor. It makes no difference to the other things running on your car.

Chris

.
One of your very best Chris.

Nice way to explain.

Gra,

 

[Graham]

A battery will never draw more than 25A or so. Even totally flat that's the max it will deliver. Given there is a winch when the winch is operating the alternator will hit maximum output so the wiring between the alternator and the battery (or winch feed) will need upgrading to cope with the maximum output of the alternator. There is no need to upgrade any other wiring.

.
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.