Thunder dc-dc charger

Yes 2nd battery was fully charged when installed

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Well maybe that's why it switches off. Doh!!

Thanks for advice

Hi Ozzie,

It has a lot to do with the modern so called “smart alternator” in most vehicles today. It would be better explained by those with more 12 volt knowledge than me, but from my understanding, once your cranking battery reaches its “full charge” the smart alternator drops back the amps. By going through a dc/dc charger, you maintain higher amps until your auxiliary batteries reach their full charge status.

Macca.

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Macca is right about "smart" or ECU controlled alternators not providing the charging needs of an auxiliary battery, but it a bit more complex than just the cranking battery reaching "full charge".

The purpose of controlled alternators is to reduce engine load under certain conditions to assist in attaining emission requirements.
A traditional uncontrolled alternator maintains a constant output in the order of 14.4 volts which cause a high charging current to the cranking battery following the engine-starting discharge. This imposes an engine load that increases emissions and if the alternator voltage output level can be reduced and delivered over a longer period of time then the emissions are reduced. The cranking battery charge is compromised but tolerable.
Unfortunately, this reduced voltage does not provide satisfactory charging of an auxiliary battery as we are seeking to charge it to its maximum storage capacity. The introduction of a dc-dc charger between the alternator and the aux. battery ensures that this battery will receive a full charge despite the low alternator voltage. It also has additional benefits such as overcoming cable voltage drop.

Well my Range Rover Sport has one of these smart alternators and I do not need a dc dc charger - the Dc Dc charger myth seems to be something pushed on this forum and less so elsewhere.

Why limit yourself to only 20 or 40 amps when you can utilise the full charging capacity - up to 180amps depending on car load.

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Well Ozzie, Using a dc-dc charger on an auxiliary battery, especially if it is Deep Cycle AGM or Lithium has a number of benefits. You do not need to avail yourself of these if you do not wish, but you may benefit from employing one.

And you ask "Why limit yourself to only 20 or 40 amps when you can utilise the full charging capacity - up to 180amps".
There is a very good reason to limit the charge rate of your aux. battery. Excessive charge current can do harm to your battery. The battery manufacturers prescribe charge rate limits, typically expressed as "20C" or the like. This means that the charge rate should not exceed 20% (in Amps) of the battery capacity in Ah. (Ampere hours). So for a 100 Ah rated battery you should not exceed 0.2 X 100 = 20 Amps. Exceeding this regularly may shorten the life of your battery.

A further reason is that batteries prefer to be charged on a profile other than just plain continuous current. A dc-dc charger operates with a built-in algorithm that adjusts the current as the charge proceeds in a fashion to benefit the battery.

As to it being "pushed" on this forum, it could just be that this forum has smarter members than some of the "elsewhere" forums. lol

The so called Smart charge alternators, I can hardly see the point of them at all, do drop the charge right off after a while, so much so the battery is often low. Emissions are emissions and I can't see why you want less initially and slightly more over a period of time. Most modern vehicles make up lost start charge immediately. Either Diesel or petrol drag the battery to start and apart from the normal current required to operate the system while travelling the normal alternator may hold at 14.2v but isn't delivering any more amps than required. So same emissions. The start stop nonsense must make a mockery of emission control while running, as it has to top it up all the time around town. Smart ones, Dumb really, make sure you need a DCDC unit wired appropriately to load the sensor so it charges an aux battery. For travellers, a plain alternator is far more reliable and easy to replace at minimal cost too. The Rover one OzzieCruiser has, might be sensing to supply voltage under load of an AUX battery and simply not be operating in the Smart zone at all. If it did work smart it wouldn't charge the aux battery as I see it. Unless a voltage and amperage monitor was constantly looked at, no one would know what was happening and when.

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RMD,

Here is what I said in a Thread back in 2013.. It seems to have been borne out by the continued and increased use of ECU controlled alternators in modern vehicles.......

........."The new "Intelligent" alternator control is intended to reduce fuel consumption and emissions in several ways.
1) The alternator output (and hence engine load) will be reduced or even ceased during acceleration to provide more power (at any given throttle) to the vehicle's wheels.
2) The alternator output will be reduced to zero during idling to reduce engine load and emissions.
3) The alternator output will raised during engine braking during deceleration to provide regenerative charging.
Projected fuel savings are 3%.
AGM cranking batteries are being introduced to allow for a more cyclic charge pattern and will frequently be operating at about 80% SOC.
Articles on this subject are hard to find on the internet without access to authoritative professional sites and some uninformed information exists.
I cannot reliably determine how this new alternator control will affect the charging of auxiliary batteries but it seems likely that at least DC-DC charging will be required and even that will need some special attention by the manufacturers. It is also possible that third parties may offer vehicle modification solutions."......

You may well not be able to "see the point of "Smart charge alternators" but it would seem that the vehicle manufacturers and the Emission Authorities can. Even small emission reductions are worthwhile when striving to conform. It may surprise you but idling emissions eclipse driving emissions due to the engine being in an increased inefficiency state at idle.

Personally, I don't like the idea of the "Start-Stop nonsense" either but its benefit is fact. May cause problems as the traffic lights change to green when stalled due to an ageing crank battery . And could be damned uncomfortable on a hot day in city peak hour unless the vehicle's air conditioner was powered by a capable dedicated battery!

There are numerous articles available on the internet dealing with this subject and its benefits. Try reading and understanding one or two.

Allan you clearly do not understand how the amps from alternator provides power to the battery - if 180amps is available it does not force these down the throat of the battery (Hi Voltage will do this) - the alternator will just provide the amps needed by the battery up to the maximum it can produce.

"Allan you clearly do not understand how the amps from alternator provides power to the battery"

That is a very big call, my friend!

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Ozzie,

It was YOU, not I, who said ..... "Why limit yourself to only 20 or 40 amps when you can utilise the full charging capacity - up to 180amps depending on car load." (That is a copy and paste)
And I think that I do have some vague idea of "how the amps from alternator provides power to the battery".

Thanks Frank. How do I continue to get into these situations? You are invited to take over. lol

Allan
Oh, I understand ok, just don't see how the tech achieves much at all in all but dense city driving. If you intend to have the Sprinter away from cities I would be providing a small conventional alternator which can be bolted on in emergencies when the Merc system goes off air. I carry a backup system.

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RMD,
I know where you are coming from. But "dense city driving" is where the majority of vehicles are, together with the worst air pollution.

I always eulogised the reliability of my 2002 Troopy due to its simplicity. I could fix almost anything with gaffer tape or fencing wire. The technology of the Sprinter will be something to behold, but with a lifetime of experience in fixing failed electronics, I am uneasy about its reliability. I'll probably need insulated fencing wire! lol (Note that I put "lol" there in case OzzieCruiser thought I was serious about insulated fence wire)

I certainly do intend having the Sprinter away from cities.... that's why I opted for the 4WD version.
And it is due for arrival TOMORROW!!!..... But I won't hold my breath!
Hope I can drive the bloody thing!

@Allan - It was YOU, not I, who said ..... "Why limit yourself to only 20 or 40 amps when you can utilise the full charging capacity - up to 180amps depending on car load." (That is a copy and paste)

If you have a 20 amp dcdc charger and the battery wants to take 30amps it will only get 20 amps - but with a larger alternator it will take what it wants.

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Exactly Ozzie, that is what I explained to you in FollowUp 4 above..... when I said "There is a very good reason to limit the charge rate of your aux. battery". You don't seem to comprehend what I am saying even though I am taking pains to express it clearly.

Sorry, but I don't think I can say anything more to you that you will appreciate.

"If you have a 20 amp dcdc charger and the battery wants to take 30amps it will only get 20 amps - but with a larger alternator it will take what it wants."

Without controls, increasingly, some batteries can accept more charge current than is good for them. And some batteries (eg some lithium, not all) can draw more current from the alternator than is good for it (the alternator). eg my lithium battery will accept 360 amps if it can get them. Pity the poor 170 amp alternator running flat chat for however long it holds up before melting. Hence the use of a DC-DC charger that is suited to or can be programmed to suit the target battery and/or the alternator.

It's a bit like a greedy person. You can eat all you want, but it's not necessarily good for you.

@Allan "Sorry, but I don't think I can say anything more to you that you will appreciate."

Now that is something we can agree on.

Frank,
You are spot on with the alternators ability to destroy itself.
A rule of thumb I was taught as an apprentice is not to run alternators above 60% continiously.
It has never let me or my customers down.
Alternators have advanced a lot since then to do with cooling and output curves so they made the units physically smaller which actually made it worse if left to idle whilst trying to charge greedy battery banks which the engineers didnt care about when designing the vehicle.
Some manufacturers give max idle outputs for their alternators which is normally around 30% of the rated output, but they will easily exceed this given the right demands.
If you have ever seen the high output units such as Neihoff ( spelling may be incorrect) 24 volt 260 amp air cooled, they are the size of a 15 litre bucket but half of that is cooling fans so they can handle high idle currents.

Ozzie, maybe you missed the bit about the battery manufacturer's specifications - or maybe youy don't care about them - but they usually specify a maximum charge current. They do this to avoid abusing the battery so that the battery (cycle) life will be something reasonable. The battery itself doesn't know about the specs, so WILL accept charge determined by applied voltage and SOC.

So when you said : "If you have a 20 amp dcdc charger and the battery wants to take 30amps it will only get 20 amps - but with a larger alternator it will take what it wants." then that is a perfect illustration. The battery manufacturer's spec may well be 20A but the hungry battery doesn't know it.

Certainly in my case with a 100Ah battery costing $600, the manufacturer's spec is 20A max. So I use a 20A DC-DC charger to protect my investment. If you choose not to do that, it's entirely your business.

Regarding a smart alternator as Allan mentioned is to avoid some emissions, they may well do that but if using a 20 or 30 amp DCDC unit the alternator cannot drop it's output to low emission causing levels while still providing a DCDC unit at 20A ++ or 30 A ++ continuously until the AUX battery bank is charged to the DC DC units specs and profile. In other words NO FREE LUNCHES even if you have a smart alternator. Most regulated 14.2 v don't charge high output for very long due to cable runs size and length to aux and battery voltage/resistance increasing as they accept charge. If a DC DC is used which tries to pump at 14.7 and sometimes beyond, the alt is still churning. The the total charge time may well be markedly increased. All such power still originates from the alternator. Travelling people could save more than the smart alternator load and subsequent fuel use, if they simply economized on weight of their vans and unnecessary gear. ie coffeee machine and useless stuff like that!

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Yes RMD, all valid points.

Of course the vehicle configuration in regard to emissions is configured to confirm to appropriate standards for a new vehicle. Once it is sold the OEM would have no responsibility (or interest) in what the owner may do to it that would affect the emissions issue.

However, there are laws regarding emission systems that I understand require an owner (or anyone else) to not interfere with the emission control system and devices and indeed, I think, that even require the owner to maintain such systems and devices to the supplied operational condition.

So it is interesting to consider if such legislation would be offended if an owner were to attach after-market devices such as DC-DC chargers that would or could interfere with the functioning of a vehicle's emission control system. Hmmm??

When fitting a second battery in a Ford Ranger the handbook states that you can either use a DC/ DC charger or consult your dealer to reprogram ( turn off?) the smart function of your alternator
Maybe you can assume by that that it is not considered tampering with the emissions aspect of the vehicle?

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Alby, you may well be right, or maybe the Ranger did not need the influence of a "smart" alternator to attain the emission target? Ford may still have fitted one in order to achieve a lower fuel consumption performance to quote in advertising. Once you have purchased the vehicle Ford would be unconcerned about your fuel consumption.
And yes, I am cynical. It is a characteristic I have developed over many years.

Or maybe it is as you suggested. I wouldn't know.