dc to dc chargers

what a load of bull from the "experts"

http://www.sterling-power.com/products-battbatt-info.htm

The limit in that situation is the battery load current, mine is around 55amp for a few minutes before it goes down to about 45amp. I have Lifeline AGM 440AH (4x6v). Most unsealed cells take only about 20-25 amp max charge anyway.

have fun
gmd

Peter

What is a suitable piece of equipment to ensure that an AGM battery in a trailer gets a full charge. Thinking of a setup with solar and anderson plugs to vehicle.

Alan

Hello Alan,

alternator/solar is certainly going to work well if it's set up properly.

The solar regulator should be set to the absorption voltage of 14.4V.

Bulk charging is done by the alternator during cruising, and the absorption is being taken care of by the solar panel whenever the motor is switched off (this is when the 4~5A from the panel isn't getting gobbled up by the ignition/ECU etc).
So the solar current will slowly push the battery voltage up to the absorption level whenever the motor is switched off.

If the sun doesn't shine, no dramas either.
The battery will just get a bit undercharged for a day or two which doesn't hurt it much.
Or, on the other hand, if the solar current is strong (lots of installed solar Watts relative to the amount of load), the battery could see an absorption voltage for longer than the recommended daily 0.5~1 hours.
In this case, just install two diodes antiparallel in series with the solar regulator output which makes the battery only see 13.6V.
Wire a switch in parallel to the diodes.
Whenever you want the battery to see the absorption voltage of 14.4V, close the switch.
If you want it to see the float voltage, open the switch.

How is that for simplicity and your hip pocket....

cheers, Peter

"Whenever a load like a fridge is connected to the battery while the DC/DC charger is also connected to the battery, it'll keep the absorption voltage up at 14.4V regardless of the battery's state of charge.
It'll only switch back to float after 12 hours. "

I don't believe this to be the case when running a compressor fridge.

Since the absorption charge is maintained until the current drops to a certain level, the worst that can happen is the absorption is maintained until the fridge stops running which happens regularly.
That's certainly how my CTEK mains smart charger works.

A threeway fridge or any load which draws current continuously would be a problem.

As long as the battery is in "cyclic use", i.e. it is discharged to less than 70%, then 14.4V float should be perfectly acceptable. In fact, it would be beneficial.
In a situation where the fridge and other loads run all the time this would normally be the case.

Hello Lex M,

let's look at some numbers:

The DC/DC unit in question has an absorption/float switch-over threshold of 0.4A.
At 14.4V, the recommended absorption/float switch-over current of a couple of 100Ah batteries is 2A.
Because this particular DC/DC charger's switch-over threshold is so low, the absorption time will be increased by an unknown number of hours.
During this prolonged absorption stage the battery loses water and suffers from excessive positive grid corrosion.
Ultimately, the charging current will taper off to the steady state current given by the applied terminal voltage of 14.4V.

Because the batteries' steady state currents @ 14.4V are in the vicinity of the 0.4A threshold, chances are the charger misses the recommended switch-over condition for the entire duration of the motor/alternator run time.

And I haven't even taken into account the standby current of the fridge, which in effect reduces this low switch-over threshold even more.

In other words, this DC/DC charger unit isn't meant to be used while any concurrent loads are connected.
And for this major shortcoming, it's definitely over-priced.

@hl,

floating any battery at 14.4V will make it gas constantly.
That's what three stage charging is all about.

cheers, Peter

Ok Peter,

I see your point, but that is why I said when the battery is in cyclic use.
It would rarely get to the stage where it is gassing at 14.4V if it is discharged by say 30Ah to 40Ah every day and that charger would probably barely manage to bring it to full charge in a day's drive.

hl,

I understand your reasoning.

But after all this charger is specced 20A...

Looking at your example of 40Ah charge, 80% of which will be reached once the charger hits absorption level, then it becomes clear that it won't take long for the battery to start gassing. 1.6 hours it takes to get to 14.4V in your example.

Allowing another 30~60 minutes for charge absorption, the total time on 14.4V ought to be 3 hours max.

In long distance driving, 3 hours is nothing, so there you have it.

cheers, Peter

"Or, on the other hand, if the solar current is strong (lots of installed solar Watts relative to the amount of load), the battery could see an absorption voltage for longer than the recommended daily 0.5~1 hours."

So what you're saying is the solar charging has the same (potential) problem as the dc-dc charger. (No pun intended).

Hello Lex M,

no, the solar charging doesn't have the same potential problems as a 20A DC/DC charger.

That's because the solar regulator's output doesn't have to be isolated from the car's 12V system like the output of a DC/DC charger.

This makes solar inherently safe in regards to over-charging while the alternator is spinning.
While the motor/alternator is on, the usual loads like ignition, ECU, injectors, plus the fridge, all draw current.
Only in the unlikely case of the solar current being higher than the sum of all these load currents, then the two batteries (starter and aux) would receive a small net charging current.

Only if the motor is turned off, the full solar current (minus fridge current) will be available for battery charging.
So there is a small chance while stationary, that the absorption voltage will be reached too early in the day, which could potentially over-charge the battery during the rest of the day.

That's why I recommended to include a couple of antiparallel diodes (bridge rectifier's most suitable and economical) in series with the aux battery.
Whenever the change-over from absorption to float needs to happen (after the battery's seen 14.4V for an hour or so), flick the diode-bypass-switch, and charging continues at a lower voltage for the rest of the sunny day.

It's not all that hard is it?

cheers, Peter

Your qoutes:-
"Or, on the other hand, if the solar current is strong (lots of installed solar Watts relative to the amount of load), the battery could see an absorption voltage for longer than the recommended daily 0.5~1 hours."

"no, the solar charging doesn't have the same potential problems as a 20A DC/DC charger. "

"So there is a small chance while stationary, that the absorption voltage will be reached too early in the day, which could potentially over-charge the battery during the rest of the day.

That's why I recommended to include a couple of antiparallel diodes (bridge rectifier's most suitable and economical) in series with the aux battery.
Whenever the change-over from absorption to float needs to happen (after the battery's seen 14.4V for an hour or so), flick the diode-bypass-switch, and charging continues at a lower voltage for the rest of the sunny day."

OK let's be consistent here.
In your opinion it doesn't have the problem but here's how to fix the problem it doesn't have.

*****

"the battery could see an absorption voltage for longer than the recommended daily 0.5~1 hours."

I've yet to see this recommendation on a battery spec. Can you supply some references please. If this was a critical parameter, I suspect that most batteries in practical use would be rapidly being destroyed by the current crop of mains and solar controllers. This doesn't seem to be the case.

Ok Peter,

You are (incorrectly) assuming that the battery will take the full 20 amps that is available from that charger until it is full. That will not be the case at all.
The charging current with a constant voltage will taper off as the battery charges. It may be 20 Amps for a short period but as the battery fills it will reduce to just a few amps, and when the battery is full it will take very little current at 14.4V, possibly not enough to gas.
Most deep cycle and AGM batteries in cyclic service are in fact designed to be charged with up to 15V if they are to realize their full capacity. 14.4 provides a good safety buffer and in practice the battery will never be overcharged unless left on that voltage for days. Many car alternators are set at close to that voltage, certainly higher than 13.8. Mine puts out 14.3V and if your theory is correct, it would cook the battery on every long drive. I can assure you it doesn't, my original battery lasted for 8 years, I topped it up maybe 5 times.
Floating a battery usually means to sit on a fixed voltage for weeks on end in standby situations with very infrequent discharges. In that case the voltage is generally around 13.5 to 13.8, but we are talking very long periods of inactivity.

Lex M,

.....OK let's be consistent here.
In your opinion it doesn't have the problem but here's how to fix the problem it doesn't have. ...

This line of yours is borne out of your tendency to read/cite things out of context and to throw around with it in a populist way.

Here's the short form of what's been said:

DC/DC overcharges during cruising.
Solar can't overcharge because it's galvanically tied to the car's 12V system, while the DC/DC isn't.
There's no Way this shortcoming of this particular DC/DC charger can be solved easily, except - switching it off.

While stationary, there's a small chance of the solar over-charging if the absorption voltage is being reached early in the day.
This can be easily prevented by a number of measures, one of which I mentioned in my earlier posts.

...I suspect that most batteries in practical use would be rapidly being destroyed by the current crop of mains and solar controllers...

If you only would read and memorise what I already stated in this thread:

The battery would be toast after sitting on 14.4V for a combined 500~1000 hours after the charging current has tapered off to the recommended switch-over threshold. Hardly a rapid way of destroying the battery...

If the correct charging termination voltages/times/thresholds would be observed the battery would be good for 50k+ hours of operation.
The choice of charging is yours.
In regards to battery specs and manufacturer's recommendations, you're most welcome to study the subject - there's plenty of research papers and results made available online.

And that's all there's is to it.

cheers, Peter

"This line of yours is borne out of your tendency to read/cite things out of context and to throw around with it in a populist way."

When the person is attacked the rest of the argument looses all credibility.
Or did I take that out of context......

I'm wasting no more of my time here.

I have been using the Arid twin charger as well for over ten years and the battery is still going strong.
120 Amp Hr job.

I have a XS25000 Ctek charger and since I will be getting an inverter I cant see any advantage in the D250S. For my situation I will be using the charger for the adsorption charging stage and not the bulk..

thoughts?

Or you can use the D250S Dual DC DC charger with a 240V 29A 12VDC power supply to make a mains powered battery charger. 29A power supply $50.
Advantage with D250S Dual you can use it as a solar regulator.

and a 1/2 charged battery

Further to above,

I like the Ranox idea because the bulk, absorption and float voltages are all user adjustable.
This can overcome voltage drop between car and camper and also can be set for differents types of batteries.
There is also temperature compensation.
I've killed several batteries while travelling over the last 20 years, usually from undercharging , and when my "redarc" dies, it will be replaced with something smarter!!

Regards
Nifty

Nifty user adjustable is not desirable. With a quality unit like a Ctek D250S if the voltage is low it pumps up the voltage to what is required. Precision units are never adjustable they maintain correct voltage in association with the included temperature sensor. Units that are adjustable are crude in design. The Ctek includes a temperature sensor. The smartest DC DC charger is the Ctek D250S or D250S Dual.

So you think ALL Lead Acid batteries need the same voltage at the same temperature ????

Mike DiD go and read the instructions on the Ctek and you will see the Ctek automatically adjusts to the correct type of battery.
Ill informed unqualified replies without research are typical of what is posted.
If a unit today is user adjustable and not automatic detection demonstrates poor design and functionality of electronics.

William,

I went looking and found Ctek instructions for their D250S but could not find any reference as to how it "automatically adjusts to the correct type of battery".
It appears to me that it uses the same algorithm for any type of battery that may be connected.
The CteK instruction states: "Charging voltage 14.4v at +25c. Battery types: All types of 12v Lead Acid, WET, MF, AGM, and most GEL batteries."

In fact, I cannot see how any charger can automatically detect which type of battery is connected and therefore select the nominated charging regime for that particular battery. Bear in mind that the manufacturers of batteries specify charging requirements that differ for the different types in particular the end-point voltage.

I would be delighted if you could direct me to an authoritative source that described how a charger can determine the battery type connected.

Incidentally, I am not suggesting that the CteK D250S is not a good charger for the purposes within its specifications or that it is inappropriate for the application under discussion in this thread.

"Units that are adjustable are crude in design."

Another Instant Internet Expert bites the dust.

Yes Mike, I agree. Doesn't look as though I am going to get a response to my question re "automatic battery detection" from WWW.

Interesting thread and as usual lots of opinions!
I confess, I am not expert in this field, but am very interested and have reserched different methods of charging multiple batteries for some time.
So basically, like most of us, I am repeating something I've read or been told by an "expert".
However, when any of these "experts" become aggressive or abusive in the way they deliver their opinion, then to me their opinion means nothing.
Needed to be said.
Nifty

Yes Nifty, if someone plays the man instead of playing the ball then it suggests that his game-skills are weak! And poor Pepper asked a simple question and, as often here, got a donnybrook for an answer.

As an electrical professional I am intrigued at the number of apparent amateurs who believe that they possess unquestionable knowledge in electrical matters and do not support their assertions with reference to a accredited source.
Even though I have a wide electrical experience I keep my expressed opinions within my knowledge. For example, whilst I have been much involved with battery charging, I have no real experience with solar systems so I keep out of that.

Fortunately, my own vehicle system is simple with both the cranking and auxiliary batteries being flooded lead-acid and in the engine bay so needing only a simple isolator system for charging. I have been able to avoid complex battery maintenance arrangements but I can see the advantage of dc-dc charging systems where the battery is located in a trailer-camper and the provision for selection of battery type.

Incidentally, I can find nothing related to Ranox that refers to possible overcharging if a load is applied to the battery during the charging activity. However I can believe that the charging procedure can be upset by a connected load. With a multi-stage charger the charge current is a component of the control program and "Bulk" or main charge termination is determined when the current decreases with battery-charge state to a pre-determined value. If a load is connected then the charger will not see the required low current state and continue bulk-charging until a timed period then switch to Maintenance Charging which is a float-charge state. However the charger may also believe that the battery is self-discharging and go to an alarm state. Suffice to say that the charger could become confused with a load connected during charging and perhaps the advice of the charger manufacturer should be sought. The alternative is to connect the load directly to the main battery whilst charging the auxiliary battery as you have done.

Hi Allan,
It's been a while since I looked at the Ranox specs, but a quick flick through mentions different options for connecting the charger with a load connected before the charger.
If you're interested I can email you a copy.
cheers, Nifty.

Hi Nifty,

Yes thanks, I am interested in those Ranox specs. Email is "allan-bull@bigpond.com"
The Ranox website that I looked at is not extensive. Perhaps because they are no longer marketing the dc-dc charger.

This is what they say on their website:
"However, due to continually increasing Australian labour costs, we can not manufacture here and sell to you at a reasonable price ($465 RRP). As we strongly desire to keep this an Australian product, we reluctantly do not have units to sell, unless conditions alter. We continue to support units already sold."

Pity! Another good Australian product becomes a victim of high Australian manufacturing costs. I was tempted to use a Ranox when I first got the Troopy but decided that it was not needed for my setup.

The idea is to power the equipment prior to the DC DC charger with automatic changeover. The DC DC charger is left to charge the battery. Circuit diagrams are available on another forum.

"This just puts out 13.7V and so is not going to be as effective as a normal three-stage bulk charge cycle. "

It will still charge to 100% capacity - it'll just take longer than 3-stage charging.