Do not test marine electronics using car battery charger.

[dxg4848]

It doesn't work . I needed 12V power to test my new toy. I have a car battery charger and I measured 13.5 VDC with my meter. So, I powered the unit up and it is completely dead. I spend time checking wires, plug, taking voltage readings with my meter, etc. The unit is completely dead. The guy I bought it from (in a local used marine electronics store) told me that he personally tested the unit and it works right. I came back to the store and asked him to power it up in front of me. He did and of course it worked great. I felt very stupid and happy that I didn't burn the unit .

[Russ]

Great topic!

Yes, you NEVER use a battery charger for a power supply. The juice is very dirty and in some cases not even DC current. Could cause a lot of damage to sensitive circuits.

--Russ

[mastreb]

Related subject: Do not use an inexpensive 120V inverter to test home automation equipment either. The square wave those things generate can kill HA equipment as well. Also learned the hard way.

And to Russ's point, most chargers generate "PDC" or Pulsed DC, which is what you get if you take 120VAC and either rectify it to DC or simply use a diode to cut off the opposite side of the AC. Then they run it through a simple 4:1 or 5:1 reducing transformer coil and call it good, because it'll charge a battery just fine.

[trdprotruck]

Depending on your power needs, I've found a cheap way to test 12 volt equipment. I am always throwing out old computers and realized the power supply provide 12 volts and is perfect when you need a 120 -> 12 volt power supply for general testing of stuff. Just make sure the watts/amps are enough for what you are hooking up.

-Randy

Just found a link that does what I'm talking about.

http://www.instructables.com/id/Convert ... r-DC-Powe/

[mastreb]

Old computer power supplies generally provide more amperage at 12v (and 5v) than anything else cheap you could buy. And very well conditioned.

Alternatively, you can just hook it up to a 12v battery (after you've charged it).

[Boblee]

Same as using solar panels direct, use but connect to a battery to flatten the voltage.

[moondancer]

Hello all. Just a side question for those in the know. I have a Honda 2000 generator that I had planned to charge and power various 12v toys and such on the boat. It is advertised as a clean power source. So my wonderment is would this be safe to use direct or should it be buffered through a battery. It doesn't hurt to bring the battery to full charge but I was thinking sometimes I just might need to charge just the one thing without draining the house power.
Thanks Mike

[kmclemore]

Hello all. Just a side question for those in the know. I have a Honda 2000 generator that I had planned to charge and power various 12v toys and such on the boat. It is advertised as a clean power source. So my wonderment is would this be safe to use direct or should it be buffered through a battery. It doesn't hurt to bring the battery to full charge but I was thinking sometimes I just might need to charge just the one thing without draining the house power.
Thanks Mike

It's safe to use straight. I have the 1000 model and it works fine with virtually everything I've plugged into it.

[kadet]

Hello all. Just a side question for those in the know. I have a Honda 2000 generator that I had planned to charge and power various 12v toys and such on the boat. It is advertised as a clean power source. So my wonderment is would this be safe to use direct or should it be buffered through a battery. It doesn't hurt to bring the battery to full charge but I was thinking sometimes I just might need to charge just the one thing without draining the house power.
Thanks Mike

It's safe to use straight. I have the 1000 model and it works fine with virtually everything I've plugged into it.

As long as you stay within the load specifications which is normally 5-8AMP at 12V for most petrol generators at idle.

The problem is that voltage of the DC output is not regulated and varies with the RPM of the generator.

So make sure not to use the gens 12v while it has a medium to big load on it off the AC, as high generator RPM can equal up to 16v which maybe too high for some applications, however most consumer electronics and other devices like portable 12v fridges can tolerate quite large voltage differences 10.4-14v some even higher. So check the specs of what you want to run direct off the gen.

The 12 volt output on a gen is a very handy back up, but if you have a proper a solar regulator it will clean up the voltage for you.

DC Chargers on generators are better than having nothing, you just have to be aware of their limitations.

[Boblee]

The Hondas are a cleaner supply than most cheapies but even so it pays to put a load on to stabilise them or stop the motor hunting, running the honda at full load would not vary the rpm otherwise the frequency would also alter.
If using any sensitive 12v appliances connect in parralell to a battery as well which absorbs peaks a bit like a capacitor.

[seahouse]

It's also worth noting that electronic devices that are made specifically for marine applications are made to withstand (filters etc) transient spikes and voltage variations, which is one thing that adds to their cost. Marine power sources are so notoriously varied and dirty; solar, wind, AC shore power, engine alternator, and switching between combinations of them, that critical devices need to be able to reliably withstand them.

BTW – my ATX bench power supply, similar to the one made in the link above, only resulted in 11.5V, and not 12V, on the “12V” tap. Close enough for anything I've used it for, though.

-Brian.

ps. dxg4848 - I'm surprised that you got any significant voltage reading at all from the battery charger leads– it must have been an older one? Most battery chargers now need to sense the voltage of the battery, and its internal resistance connected to the leads before any voltage is outputted.

[dxg4848]

ps. dxg4848 - I'm surprised that you got any significant voltage reading at all from the battery charger leads– it must have been an older one? Most battery chargers now need to sense the voltage of the battery, and its internal resistance connected to the leads before any voltage is outputted.

It is an old and chip battery charger. It has two settings 2A slow charge and 10A fast charge. When it is set for 2A I measure 11.5 VDC with digital multimeter when battery charger leads are not connected to anything. When it is set for 10A I measure 13.5 VDC. I realize now that it is dirty (unfiltered) DC. Good thing that the device I was trying to power up was blocking that dirty power even if I measured 12 VDC with my meter while the device was connected. The device appeared dead but no damage was done.