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I used to have 2 Interstate 6V Deep Cycle Batteries rated at 225Ah. They are good batteries but they are also very heavy, for a combined weight of 124lbs. For the little electricity that I use, I found this to be overkill.
Looking at alternative options, Lithium batteries are becoming more common and cheaper in the RV world. Yes, they still cost more upfront, but they will also last longer and most of all, they are a fraction of the weight.
I bought a 100Ah 12.8V Lithium Battery from a Canadian company called Lynac Lithium. Considering that you can discharge Lithium batteries to 20% – as opposed to Lead Acid to only 50% – I only needed about roughly half the hourly amperage that I would have had from my Lead Acid batteries. The battery I got weighs only about 30lbs, much better than 124lbs.
Since Lithium batteries don’t have the venting requirements that are needed for Lead Acids, I was able to install the battery inside my trailer, under the master bed in the front. Moving the battery closer towards the axle reduces the trailer tongue weight.
In most cases, you cannot simply just swap out Lead Acid batteries with Lithium. Yes, it sort of works, but you may be reducing the life span of your Lithium batteries if you don’t make the proper adjustments. Lithium batteries have different requirements on how they need to be charged, as opposed to traditional batteries such as Lead Acid and Gel. In my trailer, there are 3 power sources that need to be considered:
- My WFCO 8735 Power Center only supports 3 Stage Lead Acid charge cycles and it won’t be suitable to properly charge Lithium batteries. I really don’t feel like messing with this unit or replacing the built-in converter with an external one such as those from Progressive Dynamics.
- When plugged into my vehicle, a trickle charge is provided. This is not desirable, especially during long trips.
- Portable solar power through a pre-wired plug on the side of my trailer. This will be acceptable as the controller on my solar panels can be reprogrammed for different battery types. It has a Lithium mode so no problems there.
In summary, what I need is a way to control the direction in which the electricity flows to or from my Lithium battery. I need to prevent electricity from going into my battery when the trailer is plugged into shore power or plugged into my towing vehicle. But I also want to be able to charge the battery from my portable solar panels.
This is where a diode comes to the rescue. It’s basically a valve that lets electricity flow one way, but stops it in the other direction. Additionally, a 3-way switch is used to:
- use the diode for 1-way electricity flow; only from the battery but not to the battery. In this state, the battery cannot be accidentally charged from undesirable sources, for instance trickle charge from the towing vehicle, or from the converter while on shore power.
- bypass the diode to allow 2-way flow of electricity; electricity can go to and from the battery. This is what I need to allow solar charging of my battery and while NOT on shore power.
- disconnect the battery; no electricity can flow to or from the battery. Ideal for when you are not using the trailer for a while and to prevent parasitic battery drain. In this state I can also charge the battery while on shore power, by plugging it into a regular household outlet via its provided charger.
I was able to use a plastic case from an old satellite dish adapter to house the parts and connections in. You may have noticed the 14AWG wires from the pictures. We only use our battery to power our lights, water pump, some 12V/5V outlets, awning and slide-out. Therefore no high demands for electricity are required, hence the lower gauge of wiring is sufficient.
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