Able

[Able]

I have a 0v - 20v DC 35 amp output power supply unit adjusted to 12v which I attach to the 12v domestic circuit aboard my yacht when next to a shore 240v AC power socket. This works well.

Does anyone out there know how or if this can be used as a reliable battery charger?

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[DavidJ]

Your boat battery will be delivering 13.5 V fully charged so to get power in you need just over 14V Unless I've missed something just crank your supply up to 14.2V and it will keep everything nicely topped up.

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[Strathglass]

I would be a bit concerned at connecting such a potential current from such a source.
How accurately can you control the output voltage? how stable is the voltage setting?

Most battery chargers reduce the output current by reducing the voltage as the battery becomes fully charged.

It would be very easy to overcharge the batteries.

When set at the correct voltage it would certainly charge the batteries but You would really need to monitor the voltage and current carefully.

Iain

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[MainlySteam]

Yes, but it will be fiddlier and slower than a real 3 (or more) stage charger. And see the warning at the end, it will be more dangerous. I would not do it as a matter of course.

I sometimes use a power supply to get a charge back on a car battery, for example, if no other alternative. If you set it (with a digital multimeter) to around 13.2 volts you won't go far wrong but the charge will be slower than a multistep charger. If you intend leaving the battery connected to the power supply with no draw on the battery for some time, drop the power supply back to 12 or a bit more volts and you can leave it forever. Measure all voltages at the battery to remove cable voltage drop from the measurements. If the power supply is not well regulated, you will have to manually check to see that the voltage does not rise to an inappropriate value as the current drops during the charge.

I would not recommend trying to emulate a stepped charger by manually changing the voltage of the power supply during the charge, but if you do, keep the charge current below 20% of the amp/hr capacity of the battery during the bulk charge (but don't exceed much over 14 volts, and you may find it has to be less, especially if a thin plated battery such as an automotive one) and go back to 13.2 or so to finish off. Watch the temperature of the battery, but it should be ok.

For the sake of avoiding flac, I will add that the voltages I have mentioned are rough and ready, perhaps a little conservative, but we are talking about a rough and ready method of charging. You may need to adjust them further if your battery is not a standard wet lead/acid.

A FINAL WARNING - check that your power supply is protected against reverse voltage being applied to its OUTPUT side, but it probably isn't - otherwise be very careful as a polarity mistake when connecting to a battery may make it, and probably you too, very sick (burns and possibility of a hydrogen explosion). I would not do it unless really stuck.

If the battery is large enough to take the 35 amps of the power supply (150 - 200 Amp/hrs or more say) then ensure that the leads from the charger are capable of carrying 35 amps continuously for the time of charging (you may find they get too hot - they probably will). Also watch the power supply, again if the battery is large enough, you may find that it will not deliver the 35 amps for the bulk charge period without overheating - it probably will overheat.

I would strongly recommend buying an el cheapo single stage small capacity charger instead if your batteries are not too big. If you have 250 amp/hours or more of capacity, put in a proper permanent charger.

Obviously, you cannot do all this if you plan on just connecting it to the batteries through one of the 12v outlets on your boat - make a mistake with managing the current below the low capacity of the outlet with a power supply capable of 35 amps and you will likely burn the boat up. Similar applies if using a small battery charger, most dc outlets on a boat will only handle quite small currents continuously.

John



<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by MainlySteam on 08/09/2003 03:45 (server time).</FONT></P>