Alternator size, does it make a difference ???

[Urge38]

Hi Guys

So I purchased a Renogy DC to DC 30a charger with MPPT (RBC3030D1S)
I understood the solar input limitations, but I was unaware that the Alternator has to be within a certain amp range.

according to the manual, it states this

In general, the working voltage of a traditional alternator ranges from 13.2V to 16V, and that of a smart alternator ranges from 12V to 16V.z For a 30A battery charger, ensure that the maximum output power of the alternator does not exceed 400W. For a 50A battery charger, ensure that the maximum output power of the alternator does not exceed 660W. To prevent overuse of the starter battery, it is essential to select the battery charger specification. The specification of the battery charger is no greater than 1.5-2 times the specification of the alternator. The battery charger and the alternator are both specified in A (amperage), for example:The specification of RBC30D1S is 30A and that of a alternator is 45A-60A. The specification of RBC50D1S is 50A and that of a alternator is 75A-100A

well I have the 30amp charger and my Alternator is a 90amp

will this have a detrimental effect???

 

[Dave in AZ]

Hi Guys

So I purchased a Renogy DC to DC 30a charger with MPPT (RBC3030D1S)
I understood the solar input limitations, but I was unaware that the Alternator has to be within a certain amp range.

according to the manual, it states this

In general, the working voltage of a traditional alternator ranges from 13.2V to 16V, and that of a smart alternator ranges from 12V to 16V.z For a 30A battery charger, ensure that the maximum output power of the alternator does not exceed 400W. For a 50A battery charger, ensure that the maximum output power of the alternator does not exceed 660W. To prevent overuse of the starter battery, it is essential to select the battery charger specification. The specification of the battery charger is no greater than 1.5-2 times the specification of the alternator. The battery charger and the alternator are both specified in A (amperage), for example:The specification of RBC30D1S is 30A and that of a alternator is 45A-60A. The specification of RBC50D1S is 50A and that of a alternator is 75A-100A

well I have the 30amp charger and my Alternator is a 90amp

will this have a detrimental effect???

90A, not much. In general you don't want to run your alternator continuously above about 70% rated power. And not in idle. Both of these will make the alternator get too hot, and can burn it up. There are various videos out, some of questionable experimental test standards (the Victron one), but nevertheless it is true.

Basic Tacoma alternator is 90A, without the tow package. When I tested mine for various loads, I got full loads 46.5A (hibeams, airco, radio, turn signal, dome light)
61A If I ran the windshield wipers.

As you can see, you really don't have another 30A to use.

My plan is to charge at 30A, 400W, at times my electrical isn't loaded up. At night with airco or rain, I for sure will stop and turn it off.

Here is my Tacoma loads thread to give you some examples

Info only: 2021 Tacoma amp draw and alternator loads tested

This thread is just for reference for those looking to use excess alternator capacity to charge a battery. Other cars should have similar loads to...

www.tacomaworld.com

 

[Urge38]

90A, not much. In general you don't want to run your alternator continuously above about 70% rated power. And not in idle. Both of these will make the alternator get too hot, and can burn it up. There are various videos out, some of questionable experimental test standards (the Victron one), but nevertheless it is true.

Basic Tacoma alternator is 90A, without the tow package. When I tested mine for various loads, I got full loads 46.5A (hibeams, airco, radio, turn signal, dome light)
61A If I ran the windshield wipers.

As you can see, you really don't have another 30A to use.

My plan is to charge at 30A, 400W, at times my electrical isn't loaded up. At night with airco or rain, I for sure will stop and turn it off.

Here is my Tacoma loads thread to give you some examples

Info only: 2021 Tacoma amp draw and alternator loads tested

This thread is just for reference for those looking to use excess alternator capacity to charge a battery. Other cars should have similar loads to...

www.tacomaworld.com

Not sure if you understood my post

The Renogy manual says to use a Alternator of a MAX output of 45a to 60a for their 30a charger

I have a 90a alternator

 

[Dave in AZ]

Not sure if you understood my post

The Renogy manual says to use a Alternator of a MAX output of 45a to 60a for their 30a charger

I have a 90a alternator

The Renogy manual was written by a Chinese guy who doesn't speak English well.
Let's rephrase your question and see if the answer becomes obvious to you:
"My dcdc charger uses 30A, the renogy manual says I need 45 to 60A alternator... Can I use a bigger alternator that can supply a lot more power to the car and charger, or do I have to stay below 60A, giving me just 30A to run my whole car, before the alternator gets hot, burns up, and leaves me stranded in the desert?"

In a perfect world, you'd have a 240A alternator and never worry!

If you don't trust the long post I gave you, which it sounds like you didn't take the time to read, then use SEARCH and read the 5000 alternator charging threads here.

 

[S Davis]

Not sure if you understood my post

The Renogy manual says to use a Alternator of a MAX output of 45a to 60a for their 30a charger

I have a 90a alternator

It is the other way around,
and they messed up whatever you got that info from.

 

[Urge38]

It is the other way around,
and they messed up whatever you got that info from.

I keep reading and re reading the manual, TBH I think it is a language barrier, and thats NOT what they mean to say, never the less its does say in English and I quote "For a 30A battery charger, ensure that the maximum output power of the alternator does not exceed 400W.)

It then goes on to say, use an aultenator 1.5 to 2 times thats of the charger and I quote "To prevent overuse of the starter battery, it is essential to select the battery charger specification. The specification of the battery charger is no greater than 1.5-2 times the specification of the alternator. The battery charger and the alternator are both specified in A (amperage), for example:The specification of RBC30D1S is 30A and that of a alternator is 45A-60A.

they need to have someone English to proofread that manual

 

[Dave in AZ]

I keep reading and re reading the manual, TBH I think it is a language barrier, and thats NOT what they mean to say, never the less its does say in English and I quote "For a 30A battery charger, ensure that the maximum output power of the alternator does not exceed 400W.)

It then goes on to say, use an aultenator 1.5 to 2 times thats of the charger and I quote "To prevent overuse of the starter battery, it is essential to select the battery charger specification. The specification of the battery charger is no greater than 1.5-2 times the specification of the alternator. The battery charger and the alternator are both specified in A (amperage), for example:The specification of RBC30D1S is 30A and that of a alternator is 45A-60A.

they need to have someone English to proofread that manual

Yah, there are like 4 incorrect statements in that manual blurb. It is terrible.

 

[Urge38]

The Renogy manual was written by a Chinese guy who doesn't speak English well.
Let's rephrase your question and see if the answer becomes obvious to you:
"My dcdc charger uses 30A, the renogy manual says I need 45 to 60A alternator... Can I use a bigger alternator that can supply a lot more power to the car and charger, or do I have to stay below 60A, giving me just 30A to run my whole car, before the alternator gets hot, burns up, and leaves me stranded in the desert?"

In a perfect world, you'd have a 240A alternator and never worry!

If you don't trust the long post I gave you, which it sounds like you didn't take the time to read, then use SEARCH and read the 5000 alternator charging threads here.

That is kind off my question, but not exactly

I cant understand why Renegy says a MAXIMUM of 45a to 60a alternator ????, I can't get my head around a Max rating, In my head, the maximum doesn't matter, as long as the alternator can handle the cars demands, plus the DC to DC charger AND a buffer

My VW T25 was fitted from factory with a 45 amp Alternator, the only extra draw I have is a Head unit (stereo) but knowing I wanted DC to DC charging, I up graded to a 90a VW alternator, giving me 45a over the factory unit

 

[Dave in AZ]

That is kind off my question, but not exactly

I cant understand why Renegy says a MAXIMUM of 45a to 60a alternator ????, I can't get my head around a Max rating, In my head, the maximum doesn't matter, as long as the alternator can handle the cars demands, plus the DC to DC charger AND a buffer

My VW T25 was fitted from factory with a 45 amp Alternator, the only extra draw I have is a Head unit (stereo) but knowing I wanted DC to DC charging, I up graded to a 90a VW alternator, giving me 45a over the factory unit

There's no getting around it. You're just gonna have to accept that a tech manual, written in China, with zero editing oversight, doesn't make actual sense...
Not sure why you're having a hard time wrapping your head around it...
Is this the first Chinese made product/manual you've seen? Because I can tell you, every single power supply etc I have, the manual is complete garbage.

This is one of several reasons I won't use Renogy. If you are a US importer, and you can't even be bothered to review and fix the manuals for your products BEFORE you have people's money, what is the chance the customer service will be able to explain things AFTER they have your money? ZERO CHANCE, as shown by many hundreds of threads here.

 

[Dave in AZ]

Oh, just to summarize for you, good job getting that 90A alternator, you'll be fine running 30A on the dcdc charger with that. If you're at max load (night, lights, airco, rain, radio) then I wouldn't run it

 

[Vigo]

There is no downside to having an alternator be capable of much higher current than your loads.

If an alternator ever momentarily produces more output current than needed, the field current of the rotor winding will be reduced by the regulator so that the output current matches the load to maintain system voltage at a certain target voltage determined from various conditions assessed by the regulator. This is all done automatically. All you have to do is not design a system that loads the alternator near max capacity at idle, or preferably very much of the time at all.

The alternator is air cooled by a shaft-mounted fan so its self-cooling ability is relatively weak at idle rpm. It is also 'geared' through pulley size ratio of drive vs driven pulleys, to not explode at engine's max rpm, which generally requires it to be spinning 'too slow to achieve maximum output' at idle rpm. The combination of those two factors means that you can't match OEM reliability levels unless the maximum load from the original electrical system, PLUS the load of your added equipment, does not surpass ~60-70% of the alternator's max current capacity. If you go over that, the alternator could suffer a shorter lifespan due to overheating at low engine speeds. The regulator MAY derate the alternator output based on temp inside the alternator, but while that would protect the alternator from bad system design, it wouldn't prevent your starter battery from draining during those derate conditions. So it's best to design the system in such a way that it does not regularly exceed 60-70% of the alternators max current rating while the engine is idling.

If you need a higher output alternator to match your loads you can probably get that, but how easy/cheap will depend on the vehicle in question. On some vehicles a higher output alternator may be either unavailable, prohibitively expensive, or require fabricating custom mounts and wiring connections. From what I have seen, the alternator charge wire on Japanese vehicles is not large enough to support anything more than the stock output current and would almost certainly need to be upgraded. The ground conductor is shared with the (much larger) starter motor and thus is already oversized for the alternator, so that side will be fine.

 

[DPC]

If your going to an alternator on a car not much I can say to help you.
But if your building an MG set you want 5 hp or more for 100 amp unit.
You wont need all that power once your running but you may need to the torque to get up to speed if your alternator does not soft sgtart.