Converter plus accessory battery?

[Furyous]

I have been using an accessory battery for my stereo, but soon I will be adding a horn, full lights, powered squirt guns(!), iPad charger, and underbody lighting. I'm concerned that even if I go with LEDs I will be limited with the amount if time I could use everything, and I would hate to get stuck at night with no lights.

If I were to wire a 48v to 12v converter in parallel with my accessory battery, would I potentially have the best of both worlds I.e. less draw from the power pack plus a continuous 12v regardless of the state of charge of the accessory battery? Would the converter in effect charge the accessory battery too?

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[Token]

I did have a backup plan for emergency lights... a simple led driving light hooked to a 12v pair, I thought of the converter, but my theory is the converter would draw more than the LED light. .. but I am really surprised at how many days a trolling battery lasts running radio/amp, phone charger, and halogen lights and other fun stuff. Have you had a test run on your 12v battery yet .
I dont understand how you can run the converter in parallel.. Wouldnt you need 2 48v packs for that?
Heres another thought.. I also have a small 12v battery.. looks like a UPS backup battery.. that can run my LED light all night..
my 2 cents is to simplify things. I do not want anything to steal from my pack voltage except the controller.

[Furyous]

Originally Posted by Token

I did have a backup plan for emergency lights... a simple led driving light hooked to a 12v pair, I thought of the converter, but my theory is the converter would draw more than the LED light. .. but I am really surprised at how many days a trolling battery lasts running radio/amp, phone charger, and halogen lights and other fun stuff. Have you had a test run on your 12v battery yet .
I dont understand how you can run the converter in parallel.. Wouldnt you need 2 48v packs for that?
Heres another thought.. I also have a small 12v battery.. looks like a UPS backup battery.. that can run my LED light all night..
my 2 cents is to simplify things. I do not want anything to steal from my pack voltage except the controller.

Good to have a backup plan. Maybe I could keep an r/c lipo battery onboard to connect to the lights should the accessory battery go down. Light, small, powerful, and will hold on to its charge for a month or so before needing to be topped off.

My idea is just like you see in custom car audio scenarios- you have two 12v batteries wired in parallel for 12v, but double the amperage. If the converter puts out 12v and the battery puts out 12v, treat the converter like it is another battery, and the system will still "see" 12v, but only the amperage would drop to the amperage(say, 30a) put out by the controller should the accessory battery completely die.


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[Token]

ok I get it.. so the converter is connected to the pack and connected to the 12v battery, and you can run in parallel or in theory turn it on to charge up or assist the 12v battery ..

[Nate]

Furyous, your idea is good. Get a 48V to 13.8V DC to DC converter. When you say "Parallel" I assume you mean hook the DC to DC (+) to battery (+) and DC to DC (-) to battery (-). If so this is correct.
A couple of things to watch with DC to DC converters, you noticed I recommend a 13.8 output? This will eliminate the need to charge your 12V battery separately. Keeping a 12V battery at 12 volts will shorten it's service life. Let the DC to DC charge the 12V while you charge the main pack.

Next you need to watch out for non-isolated DC to DC units. The non-isolated ones are less expensive and will work as long as you are very careful with your negative lead from your main pack. A floating ground or neg lead can cause a reverse voltage through the negative lead of the 12V accessory, it won't like this.

Enough info to digest for now....

[Furyous]

Exactly. Could eve be set to turn on if the accessory battery reached 11.8v or so. That way it wouldn't even interfere with the power pack unless it was necessary.


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[Furyous]

Originally Posted by Nate

Furyous, your idea is good. Get a 48V to 13.8V DC to DC converter. When you say "Parallel" I assume you mean hook the DC to DC (+) to battery (+) and DC to DC (-) to battery (-). If so this is correct.
A couple of things to watch with DC to DC converters, you noticed I recommend a 13.8 output? This will eliminate the need to charge your 12V battery separately. Keeping a 12V battery at 12 volts will shorten it's service life. Let the DC to DC charge the 12V while you charge the main pack.

Next you need to watch out for non-isolated DC to DC units. The non-isolated ones are less expensive and will work as long as you are very careful with your negative lead from your main pack. A floating ground or neg lead can cause a reverse voltage through the negative lead of the 12V accessory, it won't like this.

Enough info to digest for now....

Awesome info, thanks Nate! If course I meant 12v in the sense that all accessory stuff is 12v. I know 12v on a 12v battery is pretty much toast.


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[Nate]

You sounded like you knew what you were talking about, just watch the DC to DC ratings. If they don't say 12V nominal with 13.5 to 14.2 float voltage then assume it won't truly charge your 12V battery.

For most accessories you don't need to worry about the non-isolated DC to DC. Just keep your input and output wires from contacting accidentally. Issues can arise if you use a 12V accessory that ties to the main pack such as volt or amp meter that has wires on the main pack but is powered by the 12V system.

[Token]

So in theory this 12v battery converter setup would also eliminate the radio cutting out under acceleration on the way home..

[Nate]

Yes, your radio will not cut out and your lights will not dim on acceleration. Depending on how the DC to DC of your choice is built it could eliminate controller noise as well in the sound system.