Want advice on series/parallel battery cables size

haha.. good one

2oldman wrote:
Hey.. I didn't write that! But, I do like monkey butts.

April Fool!:B

Hey.. I didn't write that!

You will find those AGM batteries right next door to the "$1 Down Payment!", Rolls Royce dealer. Try and puzzle out four Lifeline group 24 batteries to fit, if you wish...

2oldman wrote:

racer4 wrote:
My primary objective is to finish a daily battery charge with the generators and the 100 amp converter in the shortest time practical.

Then you should consider AGM batteries, not just for that, but for the cleanliness and NO maintenance.

I like the faster charging capability of AGM, but the prices seem to be about twice as much as a Trojan T-125.

The battery compartment on current Cedar Creeks is sized for four GC-2 batteries. Each being about 7.1 W x 10.30 L x 11.1 H. I see Trojan has a Reliant T105-AGM that will fit. But it is hard to find a price for.

Does anyone know of a good AGM that fits in a GC-2 foot print, has about 240AH capacity (4 batts total ~480AH @ 12V), and is easy to buy at a price that won't scare most people away.

racer4 wrote:
My primary objective is to finish a daily battery charge with the generators and the 100 amp converter in the shortest time practical. When boondocking, the residential refrigerator will use about 150AH (estimate) daily of battery capacity.

With respect to the solar panel supply side of your power distribution system, your objective could easily be satisfied simply with cabling as small as 4 AWG... depending upon length. Assuming a worst-case peak current of 33A at 12 Vdc during the mid-afternoon period of maximum sunshine, your power loss over a 10 foot length of cable would be approximately 5 watts out of 400 W - a little over 1%. It would be twice that for a 20-foot run.

Keep in mind that your power distribution system is undoubtedly equipped with multiple self-resettable circuit breakers, ranging in capacity from 10A to 50A. In the overwhelming majority of RVs, these will be the inexpensive thermal-actuated variety that generally retail for around $7.50 each online. OEMs probably pay a buck apiece. Typically, you would have a separate breaker located at each end of a long cable run.

These circuit breakers are simple, fairly reliable devices that operate by routing the current through a low-impedance bi-metal strip contact that expands as the resistance causes the metal to heat up and expand in a non-uniform manner that results in one metal to expand greater than the other, causing the contacts to open. With no current running through it any longer, the metals gradually cool and contract, re-closing the contacts and permitting current to flow once again.... self resetting.

Although cheap and reliable, these circuit breakers are hardly efficient, typically requiring from 10W to 15W or more to operate. More power is required to actuate a high rated breaker because of the heavier metal strips. This means that if you are running 30A through a 50A thermal breaker, you are losing approximately 9W to each of your breakers alone at peak current. NOTE: Yes, I realize it is somewhat non-linear due to thermal conductivity considerations resulting in varying resistance within the breaker over time, but close enough for this discussion.

Bottom line, if losing 5W of solar power output due to use of 4 AWG cable is a concern for you, then you need to take a real hard look at the rest of your system and eliminate the more serious parasitic losses. High-efficiency circuit breakers that require only 1 to 2W to operate are available, but be prepared to spend $45 to $75 apiece, depending upon how you source them and the quantity that you're willing to purchase.

My advice is to concentrate instead upon achieving a balanced power distribution system that utilizes components matched to your real needs. Go back to the voltage drop calculator and see whether smaller cables will do. Seriously, I think you would be fine with 4 AWG or even 6 AWG cables on the solar side for runs of up to 20 feet and 2 AWG would be more than sufficient for the high-power applications.

You'd be better off focusing your attention upon achieving high-quality, low-impedance connections for your terminal lugs to eliminate potential losses at the ends of your cables. These are particularly bad because they tend to worsen over time and can eventually lead to problems. As I mentioned previously, also take a hard look at component such as battery separators, as the 1.5 to 2.0 A required to hold the relays in the "connected" state to charge both sets of batteries is continuous, and remains long after the sun has gone down on your solar panels and/or you've turned off your generator. In fact, this parasite will persist until it has literally drained your batteries down to the lower switching voltage.

racer4 wrote:
My primary objective is to finish a daily battery charge with the generators and the 100 amp converter in the shortest time practical.

Then you should consider AGM batteries, not just for that, but for the cleanliness and NO maintenance.

racer4 wrote:
OP here.

My primary objective is to finish a daily battery charge with the generators and the 100 amp converter in the shortest time practical. When boondocking, the residential refrigerator will use about 150AH (estimate) daily of battery capacity.

So I want to choose cables that will help with that daily charge and help the 200 watt (or 400 watt) solar panel(s) get the most AH into the batteries as is practical.

I believe your initial assumptions are a bit skewed and why wouldn't they be since your power use hasn't been documented or probably even been researched by the mfg of your RV, An owner is left to find out on his own and adjust electrical matters on his own.

I use a small 120 V dorm fridge and my research shows that power consumption is not that different from a full sized box. The larger fridge will consume more power because of a larger freezer compartment but is better insulated. I average 40AH-60AH/day. Your larger fridge may consume 100AH/day but that would be the maximum.

With 400W of solar charging available and fairly good insolation conditions, your batteries should be fully charged by the afternoon. The use of a generator may not be necessary. Your power consumption will also be defined by the other devices you use like alarms, entertainment gear, battery chargers for phones and computers, the draw of the fridge, water heater, and furnace, and others. I would be surprised if you need the generator during good, sunny conditions. There are those rainy/cloudy days or parking in a tree canopy that makes an available generator a "must have".

Good luck with your new rig!

Rough Amazon prices:
1/0- 20' 46.00
2/0- 20' 63.00
4/0- 20' 86.00 (including 5 4/0 3/8" copper lugs)
Since my last cables lasted 12-13 years...my reasoning is, YES, over-kill, no doubt, but cost over the life time of the cables, a bargain! If I was re-running cable to my inverter(2500 watt), I certainly would have used 4/0 cable too...but for a 1996 MH, the old cables have held up well(knock on wood).

To the OP...I guess it's up to you and what makes you happy, whatever you decide, I'm sure it will be Great! :-)