power supply mode on Battery charger(s)

Submitted: Thursday, Mar 28, 2013 at 07:37
ThreadID: 101344 Views:7350 Replies:5 FollowUps:8
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An early good morning to all.
I have a projecta 2500 in my caravan which has a 13.7 volt supply charge mode. The caravan has a Nova kool 12 volt only fridge/freezer. Projecta recommend the power supply mode be used when running appliances, which we always are, with the Nova kool.
What is happening to the battery if we do use the supply charge mode?
Now for a second poser. Are there battery chargers which can be connected direct to a 12 volt appliance & bypass the battery should say the battery be out of service?. You can not do this with a Projecta.
May everyone have a wonderful Easter. Stay safe. Daz
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Reply By: olcoolone - Thursday, Mar 28, 2013 at 08:42

Thursday, Mar 28, 2013 at 08:42
You can run your 2500 all the time as a charger and when you run appliances your pulling power out the battery and the charger is putting it back in....... think of it as a car charging system, you don't turn everything of to charge the battery back up whilst your driving....... your 2500 is no different to an alternator, just a bit smarter.

As for supply mode all your battery is doing is going along for a ride, in supply mode you could disconnect the battery and still 13.7v from the charger....... the only time it will not deliver voltage is if it is set on normal charge mode and the battery is removed.
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Follow Up By: Member - daz (SA) - Thursday, Mar 28, 2013 at 11:11

Thursday, Mar 28, 2013 at 11:11
Thanks Olcool1
Sorry.. But the Projecta will not run 12 volt appliances on supply mode unless the battery is there as a host, I believe there are chargers that can supply a constant 13.7 volt direct to an appliance with out the need for a battery. Is this so??
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Follow Up By: Allan B (Member, SunCoast) - Thursday, Mar 28, 2013 at 12:32

Thursday, Mar 28, 2013 at 12:32
Yes Daz, You are correct that the Projecta charger will not operate in 'power supply' mode unless a battery is connected. It then operates in a constant 'float' mode at 13.8 volts.

Some chargers such as my Ctek will operate in 'supply mode' without the need of a battery connected. Useful in the workshop for testing and operating 12v accessories.

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Follow Up By: olcoolone - Saturday, Mar 30, 2013 at 20:22

Saturday, Mar 30, 2013 at 20:22
Sounds like a clever bit of marketing on Projecta's side...
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Follow Up By: Allan B (Member, SunCoast) - Saturday, Mar 30, 2013 at 21:24

Saturday, Mar 30, 2013 at 21:24
How's that Olcoolone?

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Reply By: Racey - Thursday, Mar 28, 2013 at 08:42

Thursday, Mar 28, 2013 at 08:42
We have a similar setup in our van. These are great chargers with the remote display and control panel which makes it very easy to switch settings. When in power supply mode the batteries are maintained in float mode @ 13.8 volts. I think the simple answer to your second question is NO. It's possible to leave the projector charger in charge mode, but you run the risk of over charging the battery because the "smarts" in the charger are not seeing the correct voltages during a charge sequence.

If you have your charger remote from inside the van, there is an extension cable available, which makes it easier to switch settings.

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Reply By: Member - Tony (ACT) - Thursday, Mar 28, 2013 at 11:32

Thursday, Mar 28, 2013 at 11:32
I think your question was 'can I run the 12v fridge off a 12v power supply' yes you can, I have one out the farm to run the UHF on the local fire channel. It can be used as a battery charger as well but better off as a 12v power supply.
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Reply By: The Bantam - Thursday, Mar 28, 2013 at 11:37

Thursday, Mar 28, 2013 at 11:37
Sorry but lest get a few things straight.

If your battery is presented with a voltage higher than its resting terminal voltage, it will charge to some degree.

SO if a battery is connected to a charger set to a "supply voltage" of 13.7 volts, the battery will be charging as long as the charger has the capacity to supply the load connected pluss some to spare.

The purpose of this "supply voltage" setting is to make the charger operate without the smarts.....it will still be operating as an older style dumb charger......but it will not be as dumb as the crude old unregulated chargers......but if the voltage is correct it will charge the battery.

SOME may operate in this mode without a battery connected...mine wont.

How various smart chargers function with with a load connected in addition to the battery varies......some of these chargers are smart enough to work this out.....others may not.

Yes it is possible to get a charger.....or a a power supply that will operate without a battery connected.

This is a "regulated power supply", this is what we used to use as a high quality battery charge before these "smart chargers" came along, and what is still commonly used in a lot of stationary and standby battery installations.

They come in two forms.....fixed voltage supplies, like are commonly used to power, allarm systems, CCTV, auto accessories CB and amateur radio equipment, and variable voltage supplies that are commonly called laboratory supplies that have a variable voltage output.
The Fixed voltage supplies may have an internal voltage adjustment.

Any voltage between 13.5 and 13.8 will charge the battery quite well and can be left connected to the battery more or less indefinitely.

It can be argued that these old style regulated supplies are more reliable chargers than the all singing all dancing smart chargers under some circumstances.
After all they have been proven in this application for decades.

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Reply By: Sand Man (SA) - Thursday, Mar 28, 2013 at 19:12

Thursday, Mar 28, 2013 at 19:12

I have a Ctek battery Charger which I use on supply mode to apply a "maintenance charge to my camper batteries.
The camper has a Ctek D250S Dual dc-dc charger which would normally operate from the vehicle alternator or solar panels if connected.
Occasionally, I use a 7 amp Ctek charger to apply and maintain the camper batteries when sitting in the shed, connected to the "alternator" charge cable.
This charger is "too smart" in normal mode of operation as it detects something else (the D250S) in the circuit and flashes a fault indicator.
When placed in supply mode however, the "smarts" are removed and it then happily applies a constant supply voltage which is then managed by the D250S dual to supply a multimode charging process to the camper batteries.

My thoughts are, in your case, when your charger is used in supply mode, you may run the risk of overcharging the batteries if left connected for a prolonged time, as the charger will supply a constant voltage and not utilize the smart charging logic it would normally apply.
Even though the fridge is drawing current from the batteries, it would not be using anything like the 25 amps being input by the charger.
As the batteries near full charge, the charger will not detect this change and lower the charging voltage. It would continue to pump in the 13.7 volts and therefore an overcharge could occur.

This is where a device such as the Ctek D250S Dual, or a dc-dc charger from Redarc, amongst others, gives added protection and a smarter charging regime.


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Follow Up By: Allan B (Member, SunCoast) - Thursday, Mar 28, 2013 at 19:48

Thursday, Mar 28, 2013 at 19:48
Bill, There would not be "25 amps being input by the charger". The charger current is determined by the difference in voltage between its output and the terminal voltage of the battery. If the battery is unladen then its terminal voltage will rise with its State of Charge until it equals the output voltage of the charger, at which time the current will fall to zero. When the fridge is running the charger will contribute the necessary current. The charger specification of '25 Amps' is the maximum it will output to a discharged battery.

It is established practice to maintain batteries 'on float' by supplying them with a fixed voltage appropriate to the battery type. in the case of lead-acid batteries this is in the order of 13.4 to 13.6, adjusted slightly for battery type and temperature. Correctly set it will not overcharge the battery. Many standby battery banks are maintained this way.

In Daz's case with a fridge load connected to the battery, the consumption by the fridge will slightly reduce the battery voltage and so cause the constant-voltage charger to contribute current to restore the battery to full charge. If the fridge ceases to consume current the battery will simply charge up to full and the charge current will taper off to essentially zero. Any internal losses in the battery will be supplied by the charger.

Daz's Projecta charger could be used in this manner so long as the battery remains connected. In fact, because of the cumulative fridge load, the battery will probably sit at slightly under full SOC rather than being at risk of overcharge.

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Follow Up By: Sand Man (SA) - Thursday, Mar 28, 2013 at 20:40

Thursday, Mar 28, 2013 at 20:40

No argument on the reduction of current as the battery reaches full charge, but I don't necessarily agree that the operation of the fridge will reduce the voltage level appropriately.

In a smart charger with a "float mode" process, the voltage will drop from (nominally) 14.2v to a level around 12.8v - 13.2v.

Only measurement on Daz's setup would determine if the voltage is low enough to achieve a proper "float charge".

Personally, I wouldn't risk it with about $700 of AGM batteries in my camper.
The investment of a good quality dc-dc smart charger gives me the confidence that the batteries will achieve a long life.
In my case, the input voltage from the AC charger in supply mode may be constant, but the D250S will compensate and output a true bulk, absorption, float charging process.


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Follow Up By: Allan B (Member, SunCoast) - Thursday, Mar 28, 2013 at 21:05

Thursday, Mar 28, 2013 at 21:05
You could well be right Bill. Up at the 'pointy end' the maintenance of batteries gets a little into Black Art. There is plenty of theory and 'scientific expression' articulated about it but in my experience no prescription is perfect for all cases. I do believe however that multi-stage chargers can get a little confused if there is any significant consumer load connected to the battery whilst charging is in progress. But I have not done exhaustive study to support my belief.

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Follow Up By: Nomadic Navara - Thursday, Mar 28, 2013 at 23:23

Thursday, Mar 28, 2013 at 23:23
Multi stage chargers switch from absorption to float when the charging current falls below a small percentage of its maximum current (this is generally in the range of 1 - 2 A.) When you apply a house load to the battery you may draw more than the 1 - 2 A from the charger, it then switches back to the absorption stage (14 + volts.)

The Projecta should be switched to the power supply mode after it has fully charged its battery to stop this reversion back into absorption mode every time the fridge starts up.
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