12V Charger as Power Supply

[Hugh Walker]

I've a spare 40A 12V charger that has a power supply mode and I've a 12V watermaker that draws about 10A. Can I connect the charger in power supply mode directly to the watermaker without connecting in a battery? I've tested it with a battery and it puts out 13.5V and 5A when the watermaker is running. Thanks in advance.

[Hugh Walker]

Sorry I should have said that the 5A was what I measured going into the battery with the charger and watermaker on, so the charger was putting out around 15A total.

[btrayfors]

Some chargers, like the Iota's, can be used this way. In fact, their basic design was for a power supply, and they only transform into smart chargers with the addition of the little IQ-4 module. I would think you'd be OK, particularly if your charger has a "power supply" setting. And, the watermaker is unlikely to be very fussy since it's draw is mostly for a DC motor. IMO, Bill

[senormechanico]

+1

Motors don't care about the small stuff.

[hellosailor]

"charger that has a power supply mode "
I would think that dedicated mode is the key to this. Some of the new chargers (even some of the Honda gensets) put out such rough or odd "DC" for charging that they can damage almost anything except a battery. But if the maker says it has a power supply mode, it probably is fine for that use.

[stevensuf]

the power supply mode is just smoothed dc, many battery chargers have lots of ripple on the dc output, this is actually good for charging batteries , but not so good for running delicate electronics, the batteries normally smooth out the dc ripple acting like large capacitors.

[goboatingnow]

Originally Posted by stevensuf

the power supply mode is just smoothed dc, many battery chargers have lots of ripple on the dc output, this is actually good for charging batteries , but not so good for running delicate electronics, the batteries normally smooth out the dc ripple acting like large capacitors.

Since the vast majority of time the batteries remain in circuit, almost all chargers can be used as a power source. In fact they do so automatically. I wouldn't recommend a battery charger be used as a power source without the batteries being in circuit for several reasons.

The ripple on modern chargers isn't much different from power supplies really.

[cbsura]

I also would like to see a good technical reply to Hugh's question. My sailboat stays plugged into shore power to keep the reefer running when I'm away. The draw is enough to keep the charger from staying at float level so my batteries end up being overcharged.

So what's wrong with installing a 3-bank charger and using 2 outputs to charge the house and starting batteries while using the third output to power the panel? It seems to me that the batteries would get fully charged and I avoid the constant cycling. Hugh didn't say it outright but I suspect that's his goal here, too. Is there a down side that I'm missing?

Thanks,
Chris

[Maine Sail]

Originally Posted by goboatingnow

I wouldn't recommend a battery charger be used as a power source without the batteries being in circuit for several reasons.

.

I use my Sterling Pro Charge Ultra as a power supply all winter long. The batteries are disconnected from the system and the PCU powers everything just perfectly.

Perhaps you can elaborate on the "why" or the "several reasons" why you would not use a charger as a power pack?

In the real world this charger has perfromed beautifully as a power pack, some do, and I suppose others don't. I've run every DC item on the boat with it in power pack mode, in fact, stuff is running out there as I type because I am working on her today.....

[goboatingnow]

The reasons are

1. The battery does act as a spike reducer and reduces ripple, some battery chargers have poor ripple control.

2 . A good power supply has good step response characteristics to load changes this prevents under or overshoot. In my experience since the battery acts as a damper, some chargers have very poor control of step responses without the battery in circuit.

3. Batteries act as a good low impedance supply, many charging circuits have poor current sink abilities and handle load dumping transients badly, this can induce significant spikes as high current loads disconnect

4. Software. Some chargers in the absence of batteries raise the voltage to absorption levels, this can be upwards of 15 volts, over a longer term this stresses certain electronics designed for an average battery voltage. Some software "hunts" for the battery changing voltage levels.

Yes some specific manufacturers have designed the chargers to work as power supplies. Though I don't think I've seen one actually say it can be used with the battery taken out of the circuit , your milage may vary.

If you have a long term need for a good DC power source, which excludes a battery in circuit , but a switch mode power supply unit, cheap as chips these days.

Dave

[btrayfors]

Dave and MaineSail...

I agree with all those reasons.

The OP asked about connecting a charger directly to the frig. My reply was based on that question, i.e., it may be fine for some chargers especially since motors are not very sensitive to ripple or transients (in fact, they cause some).

The Iota's can be used as power supplies and are advertised as such. They have excellent regulation and clean output, with very low RFI so can even be used to power SSB radios.

Other chargers may have a "power supply" mode as well.

Of course, whenever possible it's better to have a battery online as well because of its function as a big bad capacitor :-)

Bill