Questions on RV Electronics

I am not an electrical engineer and consequently I struggle in understanding the various electrical terms and vocabulary that everyone in this forum is comfortable with. Please enlighten me so that I can get up to speed with all of you.

As everyone in this forum knows there are many formulae that govern electricity and the most basic of these formulae being.... Watts = Amps x Volts.

However, I have been told that each time electricity is converted (or inverted) from DC to AC or vice versa, there is a loss of electrical power.

In addition, the distance between various components also affect the efficiency rate in terms conversion or inversion. And solar panels are not very efficient.

Moreover, the stock AGM batteries (2 x 6 volt) should not be discharged to a level more than 50% of maximum storage power since discharging more than 50% will significantly reduce the life of these batteries. If Lithium-ion batteries are used, these can be discharged up to 10 to 20%.

Therefore, my questions are as follows:

(1) The stock batteries (2 x 6 volts) are rated at maximum storage of 220 amp hours. However, since these are AGM batteries, it is recommended to not discharge them for more than 50% of total storage. Therefore, 110 amp hours is the maximum that can be used without a recharge. Is this correct?

(2) The 160W solar panel option. Does anyone know the correct amp hours for CH's solar panel? A simple computation will provide an answer of 160W / 12V = 13.3 Amps. However, since solar panels are notoriously inefficient I would imagine a loss factor of 1/3 or 0.333 which would result in approximately 8.93 amps. If this is correct, it would take 12.3 hours to recharge 110 amps or 50% of battery storage capacity, assuming no discharge. Is this correct? This does not seem to be a lot of electricity. How many panels or wattage do the other owners have?

(3) Although the maximum output of inverters should be determined by the estimated usage, the inverter output is also limited by the total battery storage capacity. Is this correct? In other words, installing a 3,000W inverter on a system with 220 Amp hours of battery capacity is an overkill.
220 amps hour x 12 volts = 2,640 watts < 3,000 watts. Moreover, since it is not recommended to discharge batteries to a level more than 50%, then the maximum inverter output over 1,320 watts is an overkill, particularly if one takes into account for inefficiency loss. At 90% efficiency, the maximum inverter output is 1320 watts x 0.9 = 1,188 watts (assuming 110 amp hours or 50% of total battery capacity). Is this correct?

(4) I have been told by CH that there is a switch on Platinum IIs that allow crank power from house batteries to start the engine when the engine battery goes dead. Has anybody dealt with this?

(5) How many USB outlets do you have? How many amps per outlet are there? Probably need around 10 amps per outlet to charge larger electronic items?

Thanks and I apologize for these dumb newbie questions.

Since no one in this forum has provided me with a reply, I contacted CH and got some indirect answers (obviously I cannot get direct replies since these questions were asked from an users' perspective rather than that of a coach builder).

The answers are listed in the order of the original post.

(1) Did not ask this question and still awaiting response from the other forum members.

(2) According to Jason Bottorff of CH, the optional solar panel is Go Power Overlander 160 watt kit.
http://gpelectric.com/products/overlander-solar-kit

I estimated 8.93 amps per hour and the actual is 8.84 amps per hour so I was very close. Jason also mentioned that most people just order one solar panel and both 240 DRT and 241 XL DRT can only accommodate two panels max. In other words, as far as these two models are concerned one cannot rely on solar panel for baseline energy needs (i.e., 8.8 or 17.6 amp hours are not sufficient for more heavy duty operating demands). Jason commented as follows:

"we took a 241XL equipped with a single panel to the RV show in Perry. We had every light on and the tv/antenna on for the entirety of the show (closed hours excluded, of course) and never had to start the vehicle. We had full sunlight most of the time. We never experienced a significant decrease in available power." so in a ideal situation one solar panel will suffice to keep the light on and allow us to watch TV.

In any case, I have come to a conclusion that solar panel(s) is (are) very important in that it (they) will allow for immediate recharge of batteries after discharge as long as the sun is out. Remember that to prolong batteries, it is best to recharge them as soon as they are discharged. In addition, solar panels will make sure your batteries are "topped off" at all times again as long as the sun is out. 100% charged batteries will always last longer than those that are not.

(3) According to Jason, there is a nominal 20% loss in inverting from 12VDC to 110VAC and therefore 1,000 watt inverter is more than capable if one assumes the battery system will not go beyond the 50% capacity level on the average (assuming the stock set of two 6V batteries at 220 amp hours).

(4) Did not ask this question and still awaiting response from the other forum members. Since engine crank battery is fundamentally different in performance characteristics compared to deep cycle house batteries, I wonder how these events affect the house batteries.

(5) According to Jason, there are no dedicated 12VDC USB charging ports in the rear section of the RV. Only in the cab with one USB port and 12V cigarette lighter port in the front cab. In other words, all of your 12VDC electronic items (mobile phones, tablets, laptops, kindle, golf GPS, etc.) need to be charged through inverted outlets. Energy from solar panel(s) and batteries are inverted from 12VDC to 110VAC and back to 12VDC to power our favorite items that are 12VDC. Thus, there is at least if not more than 20% energy loss each time we recharge our toys while dry camping, unless the generator is turned on. This is a waste of energy over a long period of time I would think. Unfortunately we have two each of these toys...

Please provide me with answers so that I can ascertain that I am heading in the right direction in understanding these complicated terms and vocabulary.

BTW...According to CH, the house batteries being located in the engine bay does not affect their output performance. What do you think about this? All batteries are affected by temperature changes and that is the reason all batteries are tested at 25 degrees centigrade (77 degrees fahrenheit). Why do most German cars locate their batteries in the trunk?


Thanks and the wife and I look forward to our RV adventures.

Sorry someone with more experience hasn't responded yet but I will take a stab at it.

1. 50% is the maximum but I read somewhere that if you shoot for 70-80% state of charge (using 20-30% of capacity) is the best for long battery life.

4. A lot of RV systems have this feature but cant say for sure about CH. My Jayco has it. I was also told I could also use this switch to start my diesel generator in case the house system is not enough. I hope to never have to use it but it is nice to know its there if needed.

pfflyer said:

1. 50% is the maximum but I read somewhere that if you shoot for 70-80% state of charge (using 20-30% of capacity) is the best for long battery life.

Click to expand...

I'm no expert either. But, as I understand it, nothing magical happens at 50%. My understanding has always been that the 50% number is simply an arbitrary rule of thumb. The lower you go, and the more often you do so, the worse it is for your battery. 50% is just an easy-to-remember and fairly safe guideline.

Again, this is just my understanding. I, too, would be interested in more authoritative data.

http://www.mpoweruk.com/life.htm

SEEepth of Discharge vs Cycle Life Chart

Depth Of Discharge (DOD)

At a given temperature and discharge rate, the amount of active chemicals transformed with each charge - discharge cycle will be proportional to the depth of discharge.

The relation between the cycle life and the depth of discharge appears to be logarithmic as shown in the graph below. In other words, the number of cycles yielded by a battery goes up exponentially the shallower the DOD. This holds for most cell chemistries.

(The curve just looks like a logarithmic curve however. It is actually a reciprocal curve drawn on logarithmic paper).

For the cost of a battery, one could install/setup power monitor

https://www.victronenergy.com/upload/documents/Quickinstallsheet_BMV70x_part1_2.pdf

Thanks so much to everyone. These posts answered questions that I haven't thought of yet.
Good to know that there are expert "mentors" at this forum.

I guess there is nothing that can be done for the house batteries in the engine bay with additional heat, but at least we can maximize the life of batteries if we follow some basic rules.

BTW...I think CH's customer service is hands down the best I have experienced so far...admittedly a small sample size. CH has so far responded within the same day for all of my queries.

It is reassuring that if we do finally end up purchasing a CH van, we will be in good hands. Hopefully CH can still support our ownership in Japan as well.