Alternators and charging batteries

[JMPC]

Hello you knowledgeable lot

I am sure someone here knows something about alternators and their battery charging abilities?

I am trying to work out how many batteries I will need to carry in order to have all the 'juice' I am likely to need while 'wild' camping.

I am able to calculate most factors, but what I know nothing about is how much electricity my car alternator is will generate in any given hour.

(I have a Nissan GR Patrol year 2000, so I guess it's quite a big alternator)

I am aware of the following...

The leisure battery is 12 volt 250 amp hours, and amps x volts = watts,
so my battery theoretically has 3000 watts to offer......only it doesn't, because I shouldn't really take it to below 40% of its capacity and when re-charging them it takes forever to charge up the last 10%, meaning in practice my battery has 1,500 usable watts to offer.

I have calculated that from when I stop in the evening, late afternoon, to when I get going again the next day, my power consumption between all my electrical items - interior lights - laptop for short period- always on fridge, etc, is about 1500 watts.

So that fits well with the battery.

I am also aware that a battery can/should only really be recharged at a speed of 10% of its total capacity, so in my case, my 250 amp hour battery can only be re-charged at 25 amps per hour. Therefore ,if it's half full I should take a careful 5 hours to re-charge it.

If my alternator is capable of producing twice that amperage (if that is what it's called when going in to the battery, forgive me, not technical/electrical,) then what I would be inclined to do is run two batteries in parallel, so they can take that level of charge between them, or 3 if possible - weight is not an issue. Thus reducing my chareg time by half. so down to 2-30 mins instead of 5.

And so my question - how much electricity is my alternator likely to produce, any ideas?

What I am ultimately trying to do it limit the amount of hours I am committed to driving just to re-charge batteries for the next stop over.

If my calculations are wrong, then please say so - I´m sure you will!


Many thanks and all the best
Jon

 

[charlieaarons]

%, meaning in practice my battery has 1,500 usable watts to offer.

I have calculated that from when I stop in the evening, late afternoon, to when I get going again the next day, my power consumption between all my electrical items - interior lights - laptop for short period- always on fridge, etc, is about 1500 watts.


Jon

You mean 1500 watt-hr or 1.5 kwh.
watt-hr or kwh is a unit of energy.
watt or kw is a unit of power: rate of energy used per unit time.
So what's your energy consumption from stopping till restarting the next day?
1500 wh?
If so, your battery is borderline for the application. What if you stop longer than overnight?
Alternator outputs vary widely from 50A to over 200A. The output should be in the owner's manual. Most alternators do not put out very well at idle speed.

Charlie

 

[JMPC]

You mean 1500 watt-hr or 1.5 kwh.
watt-hr or kwh is a unit of energy.
watt or kw is a unit of power: rate of energy used per unit time.
So what's your energy consumption from stopping till restarting the next day?
1500 wh?
If so, your battery is borderline for the application. What if you stop longer than overnight?
Alternator outputs vary widely from 50A to over 200A. The output should be in the owner's manual. Most alternators do not put out very well at idle speed.

Charlie

Wonderful, thanks Charlie - I had not thought of looking in the owners manual!
And if the laternator will offer 100A then I can justify the extra battery. Great, thanks for taking the time to reply

 

[Herbie]

I am also aware that a battery can/should only really be recharged at a speed of 10% of its total capacity

Depends on the battery. 1/10 C (10% of capacity) is a very low charging rate. If you use AGM batteries, they can be charged at 1C or higher, which means the batteries can be recharged much faster (if your Alternator is up to it).

 

[wrcsixeight]

One thing critical to maximizing alternator charging current is the length and thickness of the cables. Stock charging systems are designed to top up a slightly depleted starting battery, not to charge that battery, and another larger Deep Cycle 'leisure' battery, that is even further away, circuit wise, from the alternator, than the engine battery is.


My alternator is rated at 130 amps, and I have not yet upgraded the stock wiring. In fact, before I knew about such things, I replaced my alternator with a higher amp version, and I unknowingly blew a fusible link right after.
An auto electrician found and replaced the 10 awg fusible link, but used a very short length of 14 awg fusible link as the replacement.

I have since added 130 watts of Solar and a battery monitor, which will also read alternator amperage, and the highest number I have ever seen from my 130 amp alternator is 64 amps. That number is of very short duration. The fusible link gets hotter and hotter and will pass no more than 24 amps, even if my 3 batteries are depleted and could absorb way more than this.

I intend on removing the stock alternator charging wiring, and running thicker cables, appropriately fused, in a shorter circuit, but have not yet done so, because the solar has had no problems keeping my batteries up. But it does irritate me greatly when there is no sunlight, and a 50 mile highway trip at night replenishes only 11 amps or less into my batteries. Before I had the battery monitor, I was assuming the alternator was fully charging the batteries in such a trip, now I know better. It is not even close.

 

[JMPC]

Depends on the battery. 1/10 C (10% of capacity) is a very low charging rate. If you use AGM batteries, they can be charged at 1C or higher, which means the batteries can be recharged much faster (if your Alternator is up to it).

Thanks, I will perhaps invest in an AGM battery instead

 

[JMPC]

One thing critical to maximizing alternator charging current is the length and thickness of the cables. Stock charging systems are designed to top up a slightly depleted starting battery, not to charge that battery, and another larger Deep Cycle 'leisure' battery, that is even further away, circuit wise, from the alternator, than the engine battery is.


My alternator is rated at 130 amps, and I have not yet upgraded the stock wiring. In fact, before I knew about such things, I replaced my alternator with a higher amp version, and I unknowingly blew a fusible link right after.
An auto electrician found and replaced the 10 awg fusible link, but used a very short length of 14 awg fusible link as the replacement.

I have since added 130 watts of Solar and a battery monitor, which will also read alternator amperage, and the highest number I have ever seen from my 130 amp alternator is 64 amps. That number is of very short duration. The fusible link gets hotter and hotter and will pass no more than 24 amps, even if my 3 batteries are depleted and could absorb way more than this.

I intend on removing the stock alternator charging wiring, and running thicker cables, appropriately fused, in a shorter circuit, but have not yet done so, because the solar has had no problems keeping my batteries up. But it does irritate me greatly when there is no sunlight, and a 50 mile highway trip at night replenishes only 11 amps or less into my batteries. Before I had the battery monitor, I was assuming the alternator was fully charging the batteries in such a trip, now I know better. It is not even close.

Thanks wrcsixeight for this. Very usefull to know about selecting wires that are up to the job. Solar is a good idea ,but won´t really work in my case, for this aplpication - I won´t bore you with details.

Thanks for your detailed reply

All the best
Jon

 

[KG6BWS]

Thanks, I will perhaps invest in an AGM battery instead

If you dont want to spend the money on an AGM battery, just go for a bigger standard battery. I have a single 1100 amp/hour battery in my Tacoma, and it runs my fridge, radios, lights...everything. My alternator is just the stock 60amp and it keeps everything going just fine. I can leave my truck off, with just the fridge going for probably about 3 days, give or take. The longest Ive left it off so far has been about 2 1/2 days, and it started up no problem.

When camping, Ive left the truck off with the ham radio, fridge, GPS and laptop all turned on, and occasional use of my rear work lights for cooking, and it lasted for not quite 2 days before it got a little weak. The truck started, but it wasnt cranking very well. Good thing I had someone there. If Im by myself, Im just a little more careful about watching the batteries.

All that being said, my setup needs a MAJOR overhaul before Id feel really comfortable basecamping without running the truck for more than a day, but that big battery Ive got definately does the job.

 

[wrcsixeight]

.........just go for a bigger standard battery. I have a single 1100 amp/hour battery in my Tacoma, and it runs my fridge, radios, lights...everything. ................ My alternator is just the stock 60amp and it keeps everything going just fine.

Did you add an extra zero there? An 1100 amp hour battery would weigh approximately 575 pounds, and would power a fridge for a lot longer than 2.5 days.

If you meant 1100 cold cranking amps, that has little to do with storage capacity rated in amp/hours.

Another thing to note is most True deep cycle batteries do not list a CCA rating, as they are not designed for starting. Which is what a CCA rating is designed to infer. Nor will a starting battery hold up well to deep cyclic use.

An alternator with a rating over 60 amps is useful, only if there is a single or multiple AGM batteries with thick cabling to absorb the extra amps, or the vehicle's electrical demands are regularly above the 60 amp threshold.

An alternator rated for higher amps will not produce any more amperage at idle speeds, unless the alternator's case is physically larger, or the drive pulley is smaller.

Most vehicle's stock charging systems lean toward safety. They are not concerned with slightly undercharging a single starting battery. They are concerned with overcharging one. A chronically overcharged battery will off gas more, and make it more succeptable to explosion. So they design the voltage regulators to limit the voltage earlier than the battery would really like, and they save money by undersizing the cable.

This makes it even more difficult for the alternator to fully charge an additional battery.

If you are going to rely solely on the alternator for charging, one should upgrade the wiring, and keep the distances between battery and alternator as short as possible. Keep in mind a warm engine and alternator produce very little current at idle speeds, and it can take anywhere from 3 to 8 hours of driving time to bring a single starting battery from needing a jumpstart to being 90% charged.

 

[ntsqd]

From my research on battery charging you can take it to as crazy of a limit as your wallet can stand. Have look at what deep water cruisers use for charge regulation to see what I mean. There are some pretty sophisticated regulators out there. Alternator output isn't just a function of rotor speed and diameter, it is also a function of the sophistication of the regulator. Compared to the deep water items, standard automotive alternator regulators are laughable in their simplicity.

Yet, they have been doing a decent job for quite a while so don't pitch them just because they're simple.

Some reading that was recommended to me, and that I've found to be helpful:
Managing 12 Volts; amazon.com

The leisure battery is 12 volt 250 amp hours, and amps x volts = watts,
so my battery theoretically has 3000 watts to offer.

Dropped a unit there, this should be 3kW-hrs. Even at 50% of that, 1500 Ah, is a very large battery. For a data point for comparison I looked up a Die Hard Platinum. Not really deep cycle battery, just wanted something to moor to. At a 20 hour rate it is only rated for 68 amp-hours.
Platinum Battery link

 

[shogun]

I am not sure that the point is whether the battery can "take" 10% charge or more. With a OEM charging system you cannot control or decide how much charge it "takes".

While running there is both a load (from items in use) and a charge requirement on the alternator. You can manage, to some degree, the load portion, but the charge is something between the batteries and voltage regulator and alternator, which you cant manage. The alternator should be sized to handle both these requirements with some buffer. Since you cant control a portion of that requirement you must oversize the alternator. Data in the form of monitor would help greatly in deciding the system needs.

Which brings up another question (which nobody wanted to touch last time) and that is the charge profile of the different types of batteries. AGMs have a different requirement in the charge profile than lead/acid. If the OEM voltage regulator is used, it is doing a "dumb" charge profile which L/A batteries dont mind. But AGMs do mind and you are, in effect, damaging your AGM battery every time you run the vehicle. This bleeds over to the "optimas are junk" thread.

I havent fully figured out the answer, but it appears that use of a marine voltage regulator with multiple charge profiles designed for AGM batteries (and a compatable alternator) would be the proper setup. Cursory research indicates those regulators run several hunderd dollars.

 

[wrcsixeight]

I agree AGM batteries require different charge voltages, and can be damaged by charging at too high a voltage. Since AGM batteries have so much less resistance, they can suck up pretty much all the amperage they want, at whatever voltage the voltage regulator allows. Any battery is gonna take what it wants, if the amount is available. AGM's can just take more.

I'm not sure exactly how voltage regulators determine the acceptable voltage, and I'm sure on modern Vehicles whose ECM controls this function, the variance between vehicles is pretty wide. I think it can be agreed that the vehicles ECM's are designed to regulate voltage for just one slightly depleted starting battery, and err on the side of caution, and undercharging. I believe they also assume the battery is the same temperature of the ECM itself, when in fact It could be a huge difference between the 2. Especially if an additional battery is placed in the vehicle far from either the starting battery or ECM.

One thing that should be noted is that on many vehicles, If the field wires from the alternator are removed from the Vehicles ECM, and routed to an aftermarket voltage regulator, the Check Engine Light will fire. Here in California, and in many states, if the CEL is illuminated, the vehicle will not pass emissions testing or inspection.

It's my opinion those who have had high quality batteries fail prematurely whilst being charged solely by the alternator, are chronically undercharged, Sulfate early, and die.

Before I got my Solar system and the battery monitor, I was replacing batteries yearly. I was wrongly assuming the driving I was doing was keeping them full. Now that I have monitoring capabilities, that I pay close attention to, I see just how little my alternator adds to the batteries. I see high voltage surface charges after a short drive and without the monitor would think they are full, when in fact they are far from it.

No doubt the Alternators and regulators for blue water sail boats are the best alternator systems designed. They are programmable for battery types and come with battery temperature sensors. In short they are designed to recharge large banks of deep cycle batteries quickly.

I don't know of any vehicle based system that takes all the factors into place for ultimate alternator charging. One might think RV's would have well designed charging systems, but all they really do is claim to have a high amperage alternator, with a regular voltage regulator, and a huge distance over undersized wire.

If money were not a factor, I would get a system like this and install a second alternator in place of my worthless AC compressor. I would then have the chassis starting battery completely removed from the house batteries

http://www.defender.com/product.jsp?path=-1|328|6421&id=819489

Here is some good reading on Alternators/ charging / wiring:
http://www.alternatorparts.com/FAQ.htm

http://www.aa1car.com/library/charging_checks.htm

 

[charlieaarons]

Dropped a unit there, this should be 3kW-hrs. Even at 50% of that, 1500 Ah, is a very large battery. For a data point for comparison I looked up a Die Hard Platinum. Not really deep cycle battery, just wanted something to moor to. At a 20 hour rate it is only rated for 68 amp-hours.]

You are getting your units messed up also.
3kwh or 3000wh is 250Ah for a 12V battery, not 1500 Ah (you have to divide by the rated voltage to convert wh to Ah)
Incidentally my 210 Ah 4D sized batteries weigh 135 lb each. A typical automotive sized 60-100 Ah battery weighs 50-70 lb.

Charlie

 

[ntsqd]

You are getting your units messed up also.
3kwh or 3000wh is 250Ah for a 12V battery, not 1500 Ah (you have to divide by the rated voltage to convert wh to Ah)
Incidentally my 210 Ah 4D sized batteries weigh 135 lb each. A typical automotive sized 60-100 Ah battery weighs 50-70 lb.

Charlie

I sure did. That should have read: "...this should be 3kW-hrs. Even at 50% of that, 1.5 kW-h, is a very large battery...."
So at 12 VDC that's still 125Ah, or roughly double that of my sample.

 

[JMPC]

Well thanks everyone for 'chipping in' - thanks for all the comprehensive replies - :Wow1:
All the best
Jon