Laptop power supply as a battery charger?

[WobblyElvis]

I have an old power supply for a Compaq laptop that puts out 18 volts DC. What would happen if I put alligator clips on the output and used it as a battery charger? It's not like I have anything to lose unless it bursts into flames.

This is the adapter
https://maraindustrial.com/cart/power-su...-2882-used.html

 

[MolaKule]

Bad idea.

 

[ClutchDisc]

Originally Posted By: MolaKule
Bad idea.


Agreed!

 

[Yah-Tah-Hey]

Won't do squat.

 

[horse123]

Originally Posted By: HosteenJorje
Won't do squat.


Either that or cause massive amounts of hydrogen gas to be released and cause an explosion

 

[JHZR2]

Your car battery wants 14.7v tops.

 

[901Memphis]

You could get away with 15v if you wanted to baby sit it with an ammeter but 18v is too much for a 12v battery.

They make proper power supplies for this.

http://www.batteryspec.com/html/Battery_Chargers.htm

 

[buck91]

How many amps does it put out? I have an amorphous crystal solar panel which I've seen get up to 18-19v in direct noon-day sun... but the amps are so low that I do not believe its unsafe for SLA batteries.

 

[Linctex]

Most automotive battery chargers put out FAR above 14 volts, anyway... otherwise, there isn't any "push".

I have a Schumacher battery charger that has three rates, and the highest setting (50 amps, fast charge) is like 26 volts or something.

Remember, a battery is "sponge". If you want it to fill faster, you push it harder.
18 volts won't hurt it a bit unless you leave it on too long.

 

[WobblyElvis]

I don't think the voltage will hurt the battery. I,m afraid the charger/adapter/power supply will get hot and burn out. It only puts out 1.9 amps at best. I may try it and keep an eye on it. Only using it as a trickle charger for a large trolling motor battery.

 

[Alfred_B]

Let us know which one explodes first -- the charger or the battery.

 

[wrcsixeight]

This power supply, if hooked to a depleted battery, will likely overheat in a few minutes as a depleted battery can accept many dozens of amps.

If hooked to a fully charged battery, monitor the voltage. 14.7v is good for topping up until specific gravity maxes out, but 14.7v indefinitely will cause positive plate shedding and excessive water usage.

1.5 amps seeking 18 volts on a healthy 100Ah fully charged battery will have it up in the 16.5v range fairly quickly, and gurgling and fizzing.

I'd not bother trying to utilize that power supply for battery charging, and certainly not without monitoring battery voltage like a hawk.

Keep some baking soda and eye protection handy.

 

[WobblyElvis]

I just tested it for a couple of hours on two fully charged batteries. It seemed to regulate the current at 1.88 amps and the unit got warm. I put a thermometer on top of it which topped out at 102F. The voltage at the battery posts reached 16.3 volts and the last battery started to fizz. I think it is usable as a 2 amp charger but over charging could be a problem.

 

[wrcsixeight]

16.2 volts is the recommended Equalization voltage of flooded deep cycle batteries( Trojan and Rolls Surrette), at 77F.

An Equalization is a forced overcharge to revert specific gravity of the electrolyte back upto maximum density across all 6 cells of a 12v battery, if possible. It is not always possible if the sulfation is hardened.

While it is a necessary procedure on a abused deep cycle battery, whose plates are thicker and denser, it is still abusive to the battery and should not be performed unless required.

Required is determined by using a hydrometer, and after several hours of holding the battery at ~14.7v does not get the specific gravity up in the 1.275 range, or the 6 cells ranges vary more than 0.015 or more.

EQ charges are likely more abusive to a starting battery whose thinner plates are less dense and more fragile.

If you want to use the power supply as a maintainer, power it for 10 minutes a day on a timer. But the power supply could also present a parasitic draw on the battery when not powered via 115vAC, negating the usefullness of this approach.

One could add a Diode of adequate amperage which would lower the max voltage, and prevent the parasitic draw. Could be a fun proiject to keep the electronics out of a landfill, for a while longer.

 

[HerrStig]

Originally Posted By: wrcsixeight
16.2 volts is the recommended Equalization voltage of flooded deep cycle batteries( Trojan and Rolls Surrette), at 77F.

An Equalization is a forced overcharge to revert specific gravity of the electrolyte back upto maximum density across all 6 cells of a 12v battery, if possible. It is not always possible if the sulfation is hardened.

While it is a necessary procedure on a abused deep cycle battery, whose plates are thicker and denser, it is still abusive to the battery and should not be performed unless required.

Required is determined by using a hydrometer, and after several hours of holding the battery at ~14.7v does not get the specific gravity up in the 1.275 range, or the 6 cells ranges vary more than 0.015 or more.

EQ charges are likely more abusive to a starting battery whose thinner plates are less dense and more fragile.

If you want to use the power supply as a maintainer, power it for 10 minutes a day on a timer. But the power supply could also present a parasitic draw on the battery when not powered via 115vAC, negating the usefullness of this approach.

One could add a Diode of adequate amperage which would lower the max voltage, and prevent the parasitic draw. Could be a fun proiject to keep the electronics out of a landfill, for a while longer.
The forward drop of a Si diode is about .7 volts.

 

[CR94]

Is 18 volts the open-circuit voltage, or the loaded voltage for that charger? (Cheap unregulated nominal 12V power supplies can have an open-circuit voltage of about 18V.) If that's the open-circuit voltage, and if the current output is modest, it should work, IF monitored carefully. Otherwise, there are a lot of potential pitfalls, as others have mentioned.
Good suggestion about the diode.

 

[WobblyElvis]

18 volts is the open circuit voltage and it appears to regulate itself to 1.9 amps. As long I don't overcharge anything, 2 amps is fine but I can't leave it unattended for long. Better than nothing.

 

[901Memphis]

Originally Posted By: WobblyElvis
18 volts is the open circuit voltage and it appears to regulate itself to 1.9 amps. As long I don't overcharge anything, 2 amps is fine but I can't leave it unattended for long. Better than nothing.


If you have no charger and need a budget unit check out the link I posted there's some very affordable units there.