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RV Batteries
By - LD Tullis
Tullis Electric


     Make sure your battery negative, Generator Ground, and "Pigtail" ground are tied together and run to the chassis of the coach. Do not connect the 120V neutral to this point, Place the neutral on an Isolated buss, [Isolated from ground] Your "pigtail" should be made up of 10/3 SO cord. For further explanation on grounding see my article on Grounding . I would highly recommend that all 120V power be protected by fuses which would then feed a main lug breaker box even though they are more difficult for the novice to trouble shoot, use motor rated or time delay such as FRN sized to the largest motor on board which would be the a/c.

     For you people with 24V systems and 12V apparatus, you might consider a scheme like this or even make up a 12V and a 24V buss and tie your loads to them, personally I will be using a > 120A 24V Alternator to replace the 120A 12V that ended up on my unit and an inverter which will run my 20A central a/c.

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     Remember, you can use [2} 6V batteries in series to make a 12V in which case in this drawing you would have [8] 6V batteries. Don’t forget to take into account the loss within the system which can be as high as 10% in a good inverter.

     I still recommend getting a reputable local electrician to wire your unit for you, a metal skinned coach, improperly wired, can be lethal and the cost should not be too excessive.

Caution, 24V should not be taken lightly, a study done years ago determined that under certain conditions, this voltage range can approximate the signal from the base of your brain to the heart and cause ventricular fribulation. [heart "locks" up]. Please install battery disconnects if they are not already in and wear eye protection when connecting batteries. An inexpensive pair of dry leather gloves can be of help also.


     MODEL 31DCM—950 MCA @ 32 DEG. OR 25 AMP FOR 3.3 HRS., In the drawing above you could draw 50amps @ 24v for 3.3hrs or 7hrs @ 1200 watts consumption (1.6hp) with 200 minutes of 50 amp draw for reserve . OR in this same drawing you could draw 50 amps @ 12v for 3.3hrs. or 3.3hrs @ 600 watts consumption (.8hp)with 200 minutes of 50 amp draw for reserve . Bear in mind that in calculating loads, you must know what the battery will produce.


     AH rating goes like this; A 300AH battery at the 10hr. rate of discharge will deliver 30mps for 10hrs before the cells drop to 1.67V ea. Or 10.02V for a 12V battery.

     Reserve capacity: Number of minutes it can be discharged @ 25A @80 F until the cell drops to 1.75Vea. or 10.5V for a 12V battery.[a reserve capacity of 100 signifies 100min.].

More Later…after we hear comments to better understand areas of gray for you.

LD Tullis
Tullis Electric

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