Thread: Alternator Capacity

I just re-read one of your earlier posts in this thread and again, Wilbur, you haven’t got a clew what your talking about.

Nothing is MATCHED to the BATTERY CHEMISTRY. Not alternators, AC battery charger or DC-DC converters.

You have just proven once again that you have read something but don’t have a clew what it means.

Please explain your claim?

Originally Posted by Wilbur

Oh and just a thought, if one was to accidentally leave the headlights on and flatten the car battery, the leads on the DC-DC convertor could be reversed to charge the car battery from even fairly well discharged house batteries. Could be useful.

Actually, most will not work from another battery because most DC-DC devices are designed to shutdown automatically once the motor stops, and the voltage drop to a level just above or at the level of a fully charged battery.

If these devices didn’t do this they would flatten the cranking battery once the motor was turned off.

There are some exceptions like the Ctek that can be ordered with a special lower cutout voltage level but as this device does no longer knows when the motor is turned off, you have to add a conventional isolator or again, you risk having the cranking battery flattened.

Originally Posted by Wilbur

At last, something I can agree with. I also dislike the added complication, but like many, I have very limited space, and with the DC-DC charger I can get away with less house batteries. Or I can have the same number of batteries and run a bigger beer fridge and do without something else......

However, having said that I will add that modern electronics are pretty reliable. Otherwise who would drive anything more modern than a 300tdi?

Oh and just a thought, if one was to accidentally leave the headlights on and flatten the car battery, the leads on the DC-DC convertor could be reversed to charge the car battery from even fairly well discharged house batteries. Could be useful.

Cheers,

Paul

Hi All

Guys ! its not April the 1st anymore, please calm down.

Ohms Law E = I x R, P = E x I

E = Voltage measured in Volts
I = Amperage measured in Amps
R = Resistance measured in Ohms
P = Power measured in Watts

Batteries, as they age, alter their internal resistance.
I say this as I now have cut the wiring to my dual battery smart? isolator, it was getting hot, both, the coil and the contacts that are rated at 200 ohms (new relay but I believe that it had tarnished contacts).

Both batteries were identical, except the one for the auxilliary was years older (maybe as much as five years), when coupled together I felt that the constant current drain was not good for the new Battery and would soon wreck it, hence the big snip !

I am quite capable of stuffing my own wiring up, so I don't get anyone else to do my own wiring, let alone pay them to do it.

Cheers Arthur

Hi Arthur, unless the old battery is actually stuffed and not holding a charge, then there should be no reason for a high current discharge from your new to your old other than that you have a low charged old battery, note not stuffed just low charged.

As to the Isolator being hot, it’s quite common for isolators and the adjoining cable ( the cable acts as a heat sink ) to be so hot you can’t hold them, so unless the isolator looked like it was about to melt, all should be fine.

If you want to play safe, leave the set up disconnected until you know you are going to be doing a longish drive, then connect everything up and let your alternator supply the current being pulled through the isolator so your cranking battery is not supplying any current.

At the end of the drive, turn your motor off and see if you still have a high current flow between the batteries.

I didn't realise that there were divided opinions on auto electronics, but if nothing else this "healthy debate" highlights to troubles that consumers exerience when trying to seek guidance on the best/correct way to do things.

Auto electronics is an area where I'll happily admit that I have very little understanding but this means that I'm at the mercy of whoever I seek advice from and it is now clear that my end solution will be determined by whatever school of thought that person comes from.

The benefit of forums such as these is that the person seeking advice can take the opinions shared and choose which camp they want to be in or go off and do more research themselves. Thanks for all your input.

Hi Wilbur,
In post No. 12 in this thread, you say "Having spent all my life as an electronic engineer, ... ". I'd be interested in knowing what your formal qualifications are in this area are (and from where). Further, I'd be interested to know of what professional institutes you are a member.

Looking forward to your reply,
Peter

Originally Posted by Bushwanderer

Hi Wilbur,
In post No. 12 in this thread, you say "Having spent all my life as an electronic engineer, ... ". I'd be interested in knowing what your formal qualifications are in this area are (and from where). Further, I'd be interested to know of what professional institutes you are a member.

Looking forward to your reply,
Peter

Candidly it is none of your business. I offer knowledge, take it or leave it. Unlike other contributors, I have invited anyone reading my post to check with other experts.

I make this final post on the subject, in point form so it is easy to understand. It will also be very easy for anyone to verify, in the apparently unlikely event that you are more interested in science than in the fun of being offensive to someone trying to offer good advice.

1. Ctek, Projecta and a thousand other companies are not joined together in an almighty conspiracy to dump useless multi-stage chargers on the market.

2. Multi-stage chargers do give better results.

3. The DC - DC convertors refferred to simply work on 12 volts instead of 240 volts, just like you can buy a 12 volt television for your camper or a 240 volt television. They are multi-stage chargers just like the 240 volt versions.

4. Most car alternators deliver 13.8 volts. AGM and many other deep cycle batteries require around 14.4 volts to fully charge.

5, 13.8 volts will NEVER be able to fully charge an AGM battery.

6. If the alternator did put out 14.4 volts continously, it would cook the AGM because once an AGM is fully charged, it requires the voltage to be dropped to a float voltage of around 13.2 volts. Leave it at a higher level and the battery will over charge and reduce its life.


I simply do not understand what is going on here. I offer knowledge that unfortunately conflicts with the forum guru, and you are all too thick-headed to even try to find out who is telling the truth. It is very disappointing. I looked at this forum as one of the more reasonable and rational ones, but now I am very disappointed and disillusioned. Go burn your house batteries up after two or three years, it costs me nothing. Mine is still good after six years.

Wilbur, you have not offered on bit of info, you have shown you have the ability to read something and not understand what you’re reading.

Again, no battery charge yet can compete with the versatility that an alternator offers.

You claim most car alternators deliver 13.8v. The average alternator output is 14.0 to 14.4v on older vehicles and on newer vehicles, like Toyotas and Land Rovers, the voltage is as low as 13.2v, and they have no problem charging all types of 12v lead acid batteries at this lower voltage, and this is fact, not what you THINK happens.
Wilbur, you have not offered one bit of useful info, all you have done is show you have the ability to read something and not understand what you’re reading.

Again, no battery charge yet can compete with the versatility that an alternator offers, and if you worked in this field, you would know that.

You claim most car alternators deliver 13.8v. The average alternator output is 14.0 to 14.4v on older vehicles and on newer vehicles, like Toyotas and Land Rovers, the voltage is as low as 13.2v, and they have no problem charging all types of 12v lead acid batteries at these lower voltages, and this is fact, not what you THINK happens.

Furthermore, D3s and D4s will charge at up to 15v and this does not effect the batteries, or are you saying you know better than the vehicle manufacturers?

Next, find one battery manufacturer that states you CAN NOT fully charge a lead acid battery with voltages as low as 13.2v.

What battery manufacturers and the makers of battery charges, including DC-DC devices, state is that the “MAXIMUM” charge voltage for standard AGMs and Gel cell batteries is 14.4v.

Now Wilbur, just to clarify this so that you finally understand what you have been reading, 14.4v is the MAXIMUM charge voltage not the required charge voltage, and the setting for the different types of batteries are there to make sure you don't over charge different battery types with the wrong "MAXIMUM" charge voltage.

Flooded wet cell batteries, and this includes most Calcium/Calcium batteries, and automotive grade AGMs can be charged with 14.7v.

Furthermore keeping these battery at the levels shown above will not cause any problems as you’re inferring and again an example to prove the point. When most people leaving home on the first day of a motoring holiday, They will do so with fully charged batteries ( at least they should be fully charged ) right from the beginning of their day’s drive. If according to you, this will cook their batteries, why doesn't it happened.

Wilbur, I have no idea of what section of electronics you come from ( if you actually do ) but it sure as hell had nothing to do with batteries.

BTW, I think Bushwanderer's question is a valid one, so why don't you want to answer it.