Charge a battery with cigarette lighter vs direct

[paullad]

I was told that if I charge my aux battery with the cigarette lighter in my vehicle it won't charge nearly as fast as if its wired directly to the alternator/starting battery because the cig lighter output is 12V and the alternator is 14.4V. Can anyone confirm this?

 

[B and C]

The voltage of the cigarette lighter and the alternator are the same whether it is 13.* or 14.*. These isn't a voltage reducer for the cigarette plug. The problem is the amps passed. The bigger the wire, the more amps can flow. Your cigarette plug probably has a 12 or 14 ga wire feeding it and fuse at 10? amps. The voltage and amps change depending on what the batteries require.

So to answer the quick charge question, the aux (house) battery won't charge fast because of wire size/fusing in the cigarette plug because it can't pass the amps required. Get a fat cable (at least 4 ga), two 150 amp fuses and a continuous duty solenoid for the best charging.

 

[paullad]

The voltage of the cigarette lighter and the alternator are the same whether it is 13.* or 14.*.  These isn't a voltage reducer for the cigarette plug.  The problem is the amps passed.  The bigger the wire, the more amps can flow.  Your cigarette plug probably has a 12 or 14 ga wire feeding it and fuse at 10? amps.  The voltage and amps change depending on what the batteries require.

So to answer the quick charge question, the aux (house) battery won't charge fast because of wire size/fusing in the cigarette plug because it can't pass the amps required.  Get a fat cable (at least 4 ga), two 150 amp fuses and a continuous duty solenoid for the best charging.

Hey Brian, do you know how much faster a battery will charge with the 4 ga wire? It will probably be 100 amp hr AGM. I need to make sure its going to be worth it. Thanks.

 

[B and C]

All depends on state of charge. Charging from the alternator requires driving for hours to recharge. There are three stages of charging, bulk is where most of the recharging takes place, then absorption where finish charging takes place and final is float where charge is maintained.

I strongly recommend going to battery university: https://batteryuniversity.com/

This will give you a foundation in batteries and charging.

 

[paullad]

All depends on state of charge.  Charging from the alternator requires driving for hours to recharge.  There are three stages of charging, bulk is where most of the recharging takes place, then absorption where finish charging takes place and final is float where charge is maintained.

I strongly recommend going to battery university: https://batteryuniversity.com/

This will give you a foundation in batteries and charging.



Thanks for the info. Not really interested in going to college for battery charging   as I'm kind of overwhelmed with my build at the moment. Just trying to figure out if the cost to upgrade the cigarette lighter is justified.

 

[Gypsy Freedom]

more importantly, unless you have some sort of manual or automatic current limitting system, your discharged battery will likely try to draw enough current from the cig plug that it will blow the fuse.

unless you have a current limitting system, your wire needs to be large enough to handle the rated output of the alternator and be fused accordingly. once you have safe wiring you will still be limited by the reduced current provided by standard alternator regulators. after a half hour or so of charging the current to the house battery will drop down around 5 amps and will never get up to a good bulk/absorption voltage. that is one of the main reasons direct charging from the engine takes so long to charge and never gets fully charged.

a 20 amp Battery to Battery (B2B) charger will charge faster and more complete. with only needing to move 20 amps you can use a much smaller wire. if the batteries are far enough apart, the savings in wire alone can significantly off set the cost of a B2B charger

if you do set up direct charging from your engine. make sure you have some sort of combiner or disconnect so when the engine is off and not charging the battery will not continue to discharge to the house battery.

 

[B and C]

By not charging a lead acid battery to full everyday, you will be replacing the battery(ies) often. We are trying to give you best practice. Do what you want.

 

[Gypsy Freedom]

personally i would not waste my time with charging from a ciggy lighter for any "house battery" my minimum upgrade would be run a pair of 10awg wires from the engine battery to the house battery. put a 40 amp fuse within a few inches of EACH battery in the positive wire. yes, BOTH ends. then also include where you can easily reach it a switch rated for 40 amps dc. chances are you will pop the fuse a few times if your house bank is low and the alt is putting out full capacity so keep a handfull of spare fuses. you can reduce current flowing through that wire if your house battery is low by only idleing the engine so the alternator is not putting out full power. you can also turn on your headlights and the heater fan. you might have to do this for 10-20 min if the battery was deeply discharged. i did this for a few years when i was broke and needed that charge from the engine. i probably popped a dozen fuses the first couple months till i got it all figured out. mske sure you shut the switch off when you shut down the engine or you could drain the starting battery.

then save your money and do it right, you will save money in the end with longer battery life and less fuel cost