Alternator charging

Farmhat · Senior Member

Alternator charging

Jaahn · Guru

Hi Joe smile

A short answer. You did not take enough out of the batteries to get the alternator to charge flat out. When you switched on the fridge the second time the alternator put in the extra amps need to maintain the batteries at 14V as it should.

I think you might also have confused the units of current by saying the fridge used 21 amps. Perhaps this should be 21amp hours. The actual amps is probably 7 as shown by the alternator going from 11 to 18 amps. Tricky these amps and amp hours hmm

The alternator probably charged at a much greater rate for a moment when the engine started, but then trimmed back when the voltage went up to 14V.

Jaahn

Peter_n_Margaret · Guru

Two reasons.....maybe 3...
1. The batteries were not down very far. At a lower state of charge the difference between the battery voltage and the alternator voltage would be greater and then the charge rate would be better.
2. The alternator voltage is too low to create a high charge rate. 14.3 or 14.6V would be much better.
...3....Maybe ..... The cable from the atlernator to the battery is too small for its length and there is therefore a voltage drop that makes it all worse.

The combination of direct alternator charging and solar when the house battery is low or the sun is poor can be very effective. If things are set up well, you can get some good bulk charge in and the solar will finish it off nicely as the alternator charge rate drops off as the battery comes up.

Cheers,
Peter

swamp · Senior Member

HI
Real world typical
Run the 3way for 4hrs= 84 AH consumed 84ah out of 240ah is approx. 35% depth of discharge . Should give a good reading from altenator
current will be up
charge voltage at batteries maybe well down . Might shock u to find out how low !

Previous was approx. only 10% discharged so altenator put back insignificant amount

hako · Guru

If your tug has a "smart" alternator the charge rate will be different to the older fixed voltage regulator. They are designed to save fuel and reduce emissions meaning minimal charge at idle, acceleration or cruise but as soon as you are on over-run they will increase charge.

Good Luck

Ron-D · Guru

When your battery runs low freecamping because theres been a few days of low sunlight,and you hook the tug up to the van to generate power back into the system the vehicle will be on idle ,will this be good enough,or should you sit in the vehicle with your foot on the throttle,I have only did this once it worked to a certain extent but we moved on an hour later ....

Jaahn · Guru

Hi Ron-D smile

When I do that in my motor home I put a 'block' on the accelerator to raise the engine revs to around 2000 or so and open the bonnet. You can usually find something to put on it to achieve this. In the old days a hand throttle was supplied in a diesel furious

I have no experience with new "smart" alternators. But I have a few gauges to see what is happening to the batteries normally, so expect you might monitor them OK also if you set up properly.

Jaahn

Aus-Kiwi · Guru

Yes this is possibly where DC to DC charger works better ? Need a regular that steps up on âloadââ. No point have flat or low battery . Then expect it to be ok over night . Make sure cables have little or no voltage drop between batteries and reg . Have little volts to play with . Charged to low - flat .

T1 Terry · Guru

Peter_n_Margaret wrote:
Two reasons.....maybe 3...
1. The batteries were not down very far. At a lower state of charge the difference between the battery voltage and the alternator voltage would be greater and then the charge rate would be better.
2. The alternator voltage is too low to create a high charge rate. 14.3 or 14.6V would be much better.
...3....Maybe ..... The cable from the atlernator to the battery is too small for its length and there is therefore a voltage drop that makes it all worse.

The combination of direct alternator charging and solar when the house battery is low or the sun is poor can be very effective. If things are set up well, you can get some good bulk charge in and the solar will finish it off nicely as the alternator charge rate drops off as the battery comes up.

Cheers,
Peter

I'd say Peter is the closest correct entry so far :lol: The 14v at the battery indicates this is as high as the alternator can get the house battery so the amps drop. Think of voltage like the down hill run required for water flow, the water level (volts) need to be high at the feed end to get a good flow (amps) at the output end, the lower the difference between the input voltage and output voltage, the lower the amps that will flow through the cable. If the cable is restrictive because it is too small, it's just like a pipe or hose that is too small, not as much can flow through as would flow through if a bigger diameter was used.

By adding the load of the fridge you effectively lowered the voltage at the house battery end and the alternator added more current (amps) to get the voltage back up to 14v.

The answer to solving the problem, add a DC to DC charger at the house battery end, sort of like a pump for electricity, it will lift the voltage to 14.4v and more amps will flow into the house battery until the 14.4v mark is reached resulting in a faster and charge to a higher state of charge. It will probably still only get the battery up to between 70%SOC and 80% SOC before the current (amps) start to taper off so the house battery voltage doesn't go so high it starts to damage it, but held at that 14.4v will ram the remaining charge in a lot faster than 14v will so a far better chance to get to the mid 90% mark before the end of the days charging. To get to a true 100% SOC requires a min of 24hrs on float charge and that would require a mains charger, no one drives that long nor does the sun shine that long wink

T1 Terry

Farmhat · Senior Member

Thanks all so far for your thoughts. I agree, "Tricky these amps and amp hours hmm " I will have to do a Pauline and say "please explain" to a few things. I would love to understand properly.

Jaahn, (or anyone) you are correct about amphours, it is what I meant. Are you saying, in my example, that the fridge discharging at the rate of 21 amphours in one hour, is equal to extra charge rate from the alternator of 7 amps when the fridge 12 volt is switched on? The same monitoring system is used to show in and out, so I would have to assume that it uses the same measurement both ways. (otherwise it couldn't show true SOC)

Peter I think the wire from tug battery to van fridge is 8 AWG/B&S. Could the alternator also have been only charging at 14 volts because the battery was not very flatand out of bulk mode? Vehicle used for test was 2015 Mitsubishi challenger. It does have some kind of shunt? on the negative battery terminal but I am sure it is not a Smart alternator as such. Wire to rear goes through a VSR switch.

Swamp, does it matter if during heavy discharge that the van battery voltage shows too low, even though we know that the resting voltage (when the discharge stops would be at an ok level?

Terry, Quote - "By adding the load of the fridge you effectively lowered the voltage at the house battery end and the alternator added more current (amps) to get the voltage back up to 14v." This is as Jaahn said. So I must be wrong in thinking the alternator would just put out (within it's limits) what ever is being asked for. Similar to when solar is charging battery, when you plug in something extra to charge, it uses extra solar over and above what the battery is asking for. (assuming panels are of sufficient size.)

I am here to learn, so sock it to me. smile Thanks.

Joe

Edit; have just found out these alternators are a computer controlled smart charger.

-- Edited by Farmhat on Friday 13th of April 2018 02:14:49 PM

-- Edited by Farmhat on Friday 13th of April 2018 03:19:01 PM

Izabarack · Guru

Farmhat wrote:
It was only putting out 11 amps to start then slowly dropped to 8 amps over 5 minutes. 14 volts were showing at the battery during charging.

That's how alternator charging works. What you took out of the battery is largely irrelevant to the Alternator. Charge current will be determined by the difference between the battery terminal voltage and the voltage put out by the Alternator. The difference in voltage between Alternator voltage and battery terminal voltage is all the potential difference that is available to overcome the internal resistance of the battery. When first on charge, the battery terminal voltage will be whatever and a few minutes after charging starts, the battery plates will develop a surface charge much closer now to the voltage being applied by the Alternator. You can convince yourself of this surface charge idea by measuring the terminal voltage on charge, immediately after a charge source is removed, and after the battery has been rested for some time. The resting allows for the surface charge on the plates to dissipate. In your example, you have already said that the battery reads 14 volts while getting charge from the Alternator. I would expect the battery to read something like 13.5 immediately after disconnecting the charge source and about 12.8 after resting for 8 hours or so, assuming the battery is in pretty good condition.

Basic Alternator theory at work why revving the guts out of the vehicle does not do anything extra over a fast idle, in your example, and why a DC to DC charger is a good idea if you want your battery up to full charge in shortest time. You could also up the regulated voltage out of the alternator for a very small improvement in charge rates.

Iza

lee33 · Newbie

Izabarack wrote:
Farmhat wrote:
It was only putting out 11 amps to start then slowly dropped to 8 amps over 5 minutes. 14 volts were showing at the battery during charging.

That's how alternator charging works. What you took out of the battery is largely irrelevant to the Alternator. Charge current will be determined by the difference between the battery terminal voltage and the voltage put out by the Alternator. The difference in voltage between Alternator voltage and battery terminal voltage is all the potential difference that is available to overcome the internal resistance of the battery. When first on charge, the battery terminal voltage will be whatever and a few minutes after charging starts, the battery plates will develop a surface charge much closer now to the voltage being applied by the Alternator. You can convince yourself of this surface charge idea by measuring the terminal voltage on charge, immediately after a charge source is removed, and after the battery has been rested for some time. The resting allows for the surface charge on the plates to dissipate. In your example, you have already said that the battery reads 14 volts while getting charge from the Alternator. I would expect the battery to read something like 13.5 immediately after disconnecting the charge source and about 12.8 after resting for 8 hours or so, assuming the battery is in pretty good condition.
Basic Alternator theory at work why revving the guts out of the vehicle does not do anything extra over a fast idle, in your example, and why a DC to DC charger is a good idea if you want your battery up to full charge in shortest time. You could also up the regulated voltage out of the alternator for a very small improvement in charge rates.

You should remember that the alternator doesn't 'put out' amps (current) - it offers a voltage, and the battery draws what current it can, as Iza has said....

Farmhat · Senior Member

lee33 wrote:
Izabarack wrote:
Farmhat wrote:
It was only putting out 11 amps to start then slowly dropped to 8 amps over 5 minutes. 14 volts were showing at the battery during charging.

That's how alternator charging works. What you took out of the battery is largely irrelevant to the Alternator. Charge current will be determined by the difference between the battery terminal voltage and the voltage put out by the Alternator. The difference in voltage between Alternator voltage and battery terminal voltage is all the potential difference that is available to overcome the internal resistance of the battery. When first on charge, the battery terminal voltage will be whatever and a few minutes after charging starts, the battery plates will develop a surface charge much closer now to the voltage being applied by the Alternator. You can convince yourself of this surface charge idea by measuring the terminal voltage on charge, immediately after a charge source is removed, and after the battery has been rested for some time. The resting allows for the surface charge on the plates to dissipate. In your example, you have already said that the battery reads 14 volts while getting charge from the Alternator. I would expect the battery to read something like 13.5 immediately after disconnecting the charge source and about 12.8 after resting for 8 hours or so, assuming the battery is in pretty good condition.
Basic Alternator theory at work why revving the guts out of the vehicle does not do anything extra over a fast idle, in your example, and why a DC to DC charger is a good idea if you want your battery up to full charge in shortest time. You could also up the regulated voltage out of the alternator for a very small improvement in charge rates.

You should remember that the alternator doesn't 'put out' amps (current) - it offers a voltage, and the battery draws what current it can, as Iza has said....

I guess the trick is ; find the best way/ways to increase the current. Is there any circumstances where a dc to dc charger would not work, or be detrimental to a 2015 challenger?

Asking a few mitsi dealerships has been a waste of air. Not one that I asked today had even heard the term 'smart' alternator. Makes one very thankful for folks around here.

Joe

Ron-D · Guru

Jaahn wrote:
Hi Ron-D
When I do that in my motor home I put a 'block' on the accelerator to raise the engine revs to around 2000 or so and open the bonnet. You can usually find something to put on it to achieve this. In the old days a hand throttle was supplied in a diesel
I have no experience with new "smart" alternators. But I have a few gauges to see what is happening to the batteries normally, so expect you might monitor them OK also if you set up properly.
Jaahn

Thanks Jaahn I will make something up at home to keep it at 2000 or close too....I have a 12vto12v system system but the extra revs from idle even with my system surely cant hurt...

-- Edited by Ron-D on Friday 13th of April 2018 04:46:24 PM

Izabarack · Guru

Farmhat wrote:

I guess the trick is ; find the best way/ways to increase the current. Is there any circumstances where a dc to dc charger would not work, or be detrimental to a 2015 challenger?

Easier to discuss if you ask for suggestions to recharge in shortest time. A seriously discharged Lead/Acid system might draw quite high currents immediately it goes on charge, for example, a battery at 11.5 volts will take a comparatively high charge rate until the dreaded surface charge has an effect. You described that kind of charge rate ramp in the initial post. A friend has a 25 Amp rated DC to DC charger and 250 AH battery bank. She uses solenoid switching to start charging from the alternator until that charge rate drops below 25 Amps then charges using the DC to DC charger. She is driving while this happens; idling to use alternator charging is arguably cost inefficient and you may need to fast idle for a long long time to recharge a depleted battery bank. This friend also has a fair bit of solar for use when camped.

Thought about LiFePo? Or happy to stay with more conventional technology for now?. I have only used solar to recharge Lithium but I am sure some with experience will offer some advice on the how effective is charging LiFePo from an alternator.

Iza

Peter_n_Margaret · Guru

Farmhat wrote:

I guess the trick is ; find the best way/ways to increase the current. Is there any circumstances where a dc to dc charger would not work, or be detrimental to a 2015 Challenger?

A DC-DC charger will give you it's rated charge from go to wo. That is because it has higher voltage that it offers the charging battery, but the maximum charge rate is limited by the capacity of the unit you purchase - usually 20 or 30A.

If you charge direct from the alternator (with or without a voltage booster) the maximum charge rate when the battery is low might be MUCH higher (I can get 70A charge from my 85A alternator). But (depending on the voltage offered) that charge rate might decrease fairly rapidly as the battery voltage comes up and the voltage more closely equals what is being offered, so getting a full charge is usually less likely than by using a DC-DC charger, especially with a long cable run to the the battery if that cable is not large enough.

Personally, the direct alternator option suits us best as the solar will still be contributing and getting a pile of charge into the batteries fast is more important than topping them up which the solar can do today or tomorrow.

EDIT - Iza types faster than me :)

I would argue that using the tug at idle to charge at 70Ah is probably more efficient than using a generator, and of course it is MUCH better if you happen to be driving somewhere.

Cheers,

Peter

-- Edited by Peter_n_Margaret on Friday 13th of April 2018 07:58:44 PM

Farmhat · Senior Member

Ok it's all coming together now and making sense. I was thinking about it almost completely back to front.

Peter I hear you when you say that 12v dc to dc chargers will give you it's rated charge from go to wo, but I still need to ask, don't they slow down the charge when the battery is getting full like other chargers to avoid over charging? If so the benefit must just be the faster charge rate in the early bulk rate stage? In other words are these dc to dc chargers like any other multi stage chargers in the way that they eventually end up on float?

Joe

-- Edited by Farmhat on Friday 13th of April 2018 10:26:14 PM

Aus-Kiwi · Guru

Yes been down this road before .We have higher AH batteries than normal engine battery. So alternator reg goes out of bulk charge . Be nice to have charger that worked on load even off deep cycle are 80% or so charged . Even a 240v smart charger 50 amp wiill supply 12-15 amps depending on battery voltage / charge .

Peter_n_Margaret · Guru

You are pretty much correct......a very rambling response follows...... :)
First observation.
Given an unlimited source of power at a "high" voltage, the battery will decide the charge rate according to its size and chemistry. It is simply a matter of how hard the voltage is pushing and the rate that the chemical reaction takes place. But the battery essentially controls the rate.

Second observation.
An alternator (at 85A or maybe even higher) is effectively an unlimited source, so if the battery is flat, the acceptance rate will be very high (subject to the voltage not being a limiting factor).
A DC-DC charger is limited in its amperage source, but not so limited in voltage, so initial acceptance rate will be the capacity of the DC-DC charger.

As the battery comes up in voltage, the voltage of the charge source will begin to determine the charge (acceptance) rate, irrespective of the amperage available from the source.
The DC-DC charger is then likely to have a higher voltage, so continue to charge at a higher rate, but it too will taper off as the voltages of the battery and the charger get closer and closer together and "float" occurs when they are about equal.
The lower the voltage of the charge source, the longer it will take to get the last bit in and this is why it will take longer from the alternator than from the DC-DC to arrive at the mythical "fully charged" state.
A "smarter" charger will maintain a higher voltage to "push" charge in beyond the optimal "float" position, but if that voltage was maintained long term, the battery would be boiled dry.
The DC-DC charger or a good 240V charger or a good solar regulator should all be "smart", so finish the job in reasonably quick time.
The standard alternator is not "smart", so while it does a great early job, it does not "finish" well.
This is why a combination of alternator PLUS solar is a solution I like.

And it must be mentioned the acceptance rate of various battery chemistries varies. AGMs (which are a form of lead acid) come in fast and slow acceptance rates. Lithium is characterised by VERY high acceptance rates. These differences become more important as the capacity of the charge source becomes larger relative to the capacity of the battery bank.
What was the question again???? :) :) :)

Cheers,
Peter

swamp · Senior Member

Hi
Farmhat
What ever u use to discharge batteries make sure the batt volts stay above 11.9v during operation as much as possible .
21 amp current draw is a little high from 240ah batts but for testing should be ok .
The discharged batts will current draw a lot from altenator ..
Need to measure the charge voltage at batts during high amp charge . This will tell u if u need bigger cable.

Izabarack · Guru

Farmhat wrote:
...... put fridge on 12 volt (which uses 21 ah) and the charge went up to 18 amps.

Better to say that the current arriving at the positive terminal went up to 18 Amps when you added the current sink that is the fridge, in parallel to the battery. Instantaneous charge current into the battery does not change but the draw on the Alternator goes up as the fridge "sucks" (horrible term but will do here) on the capacity of the Alternator. The Alternator regulator pops in at this time to check its set value is being put out, as it is designed to do. Any voltage drop seen at the battery terminal will always be a function of simple Ohm's law calculations of an increased voltage drop along the resistance of the conductors between Alternator output terminal and the positive terminal of the battery as the current increased.

Iza

Farmhat · Senior Member

Wow what an great education I have gotten here on this subject. I want to thank each and every one of you.

Lastly I have one further thing to add to my understanding. Does charge from solar panels and regulators behave the same, whereby it is the battery calling for charge and the charge source trying to keep up the voltage. D0 PWM regulators essentially do the same at the end of the day as an alternator but with their on and off magic way of doing it?

Joe

T1 Terry · Guru

Farmhat wrote:
Wow what an great education I have gotten here on this subject. I want to thank each and every one of you.
Lastly I have one further thing to add to my understanding. Does charge from solar panels and regulators behave the same, whereby it is the battery calling for charge and the charge source trying to keep up the voltage. D0 PWM regulators essentially do the same at the end of the day as an alternator but with their on and off magic way of doing it?
Joe

Sort of, the solar panel voltage is higher than the alternator voltage but it often can't supply more than the battery can take. When this happens all the solar panels can push out is "sucked" into the battery without being able to lift the battery voltage higher than the 14.4v or what ever the end of boost stage is set at. During this time a PWM controller is just "on" feeding all that is available from the solar to the battery. The PWM regulator does not alter the solar voltage in any way, it is because the solar can not meet the demands of the battery that the solar voltage is pulled down close to the battery voltage. It isn't until the battery can't take all the solar can supply does the voltage climb above the end of boost stage (14.4v), then the PWM regulator rapidly turns the solar on - off - on to stop the voltage climbing any higher.

The alternator has a voltage regulator that won't allow the output voltage to go above 14v roughly for the older type and as low as 13.2v for the newest computer controlled smart alternators.

Now to throw something else in, using a DC to DC charger that is also a solar regulator is only of any real value for connecting portable panels because only one or the other is likely to be used at the one time. The idea is to have both the roof top solar and DC to DC charging at the same time to get the battery up to the 14.4v state as fast as possible. If the roof top solar is connected to the DC to DC charger only one or the other will be doing the charging, not both at the same time, so a big part of the charging system isn't being used. Something to think about when looking for that ideal DC to DC charger and solar regulator, it doesn't go well if you try to get both in the one package.

T1 Terry

Jaahn · Guru

Hi smile

Been a great discussion so far thanks to Peter and Terry mainly. Read and learn. biggrin

Just another comment about alternators. Some people think they magically produce a perfect voltage 14+ V or there abouts but actually they control just by switching on and off too. hmm

The field is switched on, and off when the voltage reaches the required voltage, even on the computer controlled ones. For technical reasons the output looks more like a ramp wave form rather than a square wave but same effect. confuse

Cheers jaahn

Farmhat · Senior Member

Thanks again everyone,

Joe

Jaahn · Guru

Farmhat wrote:
Thanks all so far for your thoughts. I agree, "Tricky these amps and amp hours " I will have to do a Pauline and say "please explain" to a few things. I would love to understand properly.
Jaahn, (or anyone) you are correct about amphours, it is what I meant. Are you saying, in my example, that the fridge discharging at the rate of 21 amphours in one hour, is equal to extra charge rate from the alternator of 7 amps when the fridge 12 volt is switched on? The same monitoring system is used to show in and out, so I would have to assume that it uses the same measurement both ways. (otherwise it couldn't show true SOC)
I am here to learn, so sock it to me. Thanks. Joe

Hi Joe smile

Always happy to help a person who want to learn wink Here is a simple explanation.

The electricity can be compared to a tap supplying water flowing in liters per minute, compared to the current flowing in Amps(A). That is the rate it is flowing at the time. May go up or down as required.

The water runs into a bucket for storage, and then it becomes quantity held, in liters . This equals a quantity held in the battery, the electricity amount stored as amp hours(AH). It may go into the battery fast at a larger current eg 20 Amps for 1 hour or it may be slower eg 5 amps for 4 hours but the battery has the same amount of 20 AmpHours(Ah) stored.

In the case of a compressor fridge using power. It turns on till it gets cold and is using, say 7 Amps working. Then it turns off for a while and uses 0 A, Then turns on for a while, then off, etc. So if it was on for 10 minutes then off for 10 minutes, it averages only 3.5A and does this for an hour it would only use 3.5AH. If it keeps going like this all day this uses 3.5AH x24 hrs = 84AH you used up from your battery. The fridge suppliers can give this figure for normal use.

Hope this help a bit.

Jaahn