Want advice on series/parallel battery cables size

[racer4]

Hi all,

I need to order some series/parallel battery cables. I have read a lot on this, used many voltage drop calculators, etc. and still would like some more experienced advice.

Here are the details and questions:

Detail 1. I have ordered a Cedar Creek 36CKTS. It has room for four GC-2 6V batteries. It has a electric only residential refrigerator. Pictures of a similar (2015 CC 32RL) setup can be seen Here. Please ignore the fact that the dealer wired it wrong (no parallel cables etc).

Detail 2. I will be supplying four Trojan T-125 batteries. The total battery bank capacity is 480 AH (20-Hr rate).

Detail 3. When the FW is not plugged into utility 120V AC, the refrigerator runs on a WFCO WF-5100 1000W inverter. It claims >80% efficiency. I figure it's max continuous draw (based on 1000W) will be 100A. Actual use will probably be closer to 40A, but I want to size the cables for the maximum possible draw.

Detail 4. I plan to add a 100A converter (Powermax PMBC-ADJ-100 or a Meanwell RSP-1500-15) with adjustable voltage output (set to ~ 14.8V) to do a daily battery charge when not plugged into utility 120V AC. It will be powered by two Honda EU2000i generators, running in parallel. I plan to plug the converter in to an electric outlet controlled by a mechanical timer (thanks Mex). This 100A converter will only be used for generator charging. The OEM WFCO 65A converter will be turned off during gen. charging and turned on when plugged into utility 120 AC electric. I may upgrade the WFCO converter, but that is another matter.

Detail 5. I will upgrade the factory battery cables if needed, at the time I add the 100A converter. It looks like they are 2 AWG, but I am not sure. The pics I linked to above show the dealer used 2 AWG series cables and they appear to be the same diameter as the factory cables.

Detail 6. I will probably buy the battery cables custom made from Genuinedealz unless I find a better source.

Detail 7. The cable lengths are 2' for the parallel cables and 1' (or less) for the series cables.


Question1. What size series/parallel battery cables should I buy? I am thinking 2 AWG minimum, and maybe bigger at 1 AWG, 1/0, or 2/0.

Question 2. What % voltage drop should I size the cables to? 1.5%, 1.25%, 1.0% ?

Question 3. What cable lug should I get? Genuinedealz (see detail 6 link) offers: Tinned Copper Lug OR Heavy Wall Tinned Copper Lug.

Thanks for your help.

Chris

[2oldman]

haha.. good one

[westend]

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

April Fool!:B

[2oldman]

Hey.. I didn't write that!

[DAWg134]

racer4 wrote:

2oldman wrote:

racer4 wrote:
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.

Lifeline GPL-4CT batteries will give you 440 AH at 12 Vdc, but they're not cheap at $299 apiece.

Still, the best decision I ever made was to substitute Concord batteries (Mil-Std version of Lifeline AGMs) for the OEM Gill flooded cell batteries on my helicopters. Instead of replacing every 12-14 months, I was getting 5 years per battery. Even though the Concords cost nearly twice as much ($840 vs 475), I was coming out way ahead... not to mention eliminating maintenance downtime. When it came time to replace the two OEM Trojans on my Roadtrek, I didn't hesitate a second.

Powerstride had the best prices last year when I purchased my GPL-4CT-6s at $250 each (free S&H), but other sellers may be more competitive today.

[MEXICOWANDERER]

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...

[racer4]

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.

[DAWg134]

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.

[2oldman]

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.

[westend]

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!

[Acampingwewillg]

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! 🙂

[racer4]

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.

[2oldman]

racer4 wrote:


One more factor I forgot to say. The FW will also have a 200W solar panel factory installed (by Cedar Creek), which I am trying to have increased to 400W. Does that make a difference in choosing the cable size?

not the battery cables..no.

[DAWg134]

I realize I will be in the minority, but I believe too many people commit cable overkill when designing their vehicle power systems. In many cases, it turns out to be a case of “penny-wise, pound-foolish” as they fail to take into consideration the total system performance and the impact of relatively high-impedance interconnections and components. A little practical knowledge regarding basic electronics will help immensely.

You are definitely on the right track by using online voltage drop calculators, as suggested by Question #2. The key is to understand precisely what you are trying to achieve and/or avoid. Are you concerned that undersized cabling will heat up under load and lead to a fire? Are you attempting to minimize power loss because you want to maximize your power system’s efficiency?

Question 1 - “What size cable?” See Question 2 - use a voltage drop calculator to appropriately size the wire for the intended amperage and the length of the run, based upon the minimum acceptable criteria you establish… plus a little bit extra for margin.

Question 2 - “What is an acceptable voltage drop?” You’ve already calculated your maximum load to be 100 Amperes. At 13.6 Vdc, a 1.5% voltage drop would be 0.204 Vdc. Would less than a quarter volt decrease likely affect any of your appliances? No. Your power (P=I*V) loss would be approximately 20 watts. Is that enough to heat up a cable to the point that nearby objects would combust or plastic melt? Unlikely, especially if the 20W are distributed over a substantial length of wire.

Question 3 - “Copper or tin?” This is almost a “plastic or paper” question… there is no “right” answer. However, unless everything else to which you’re connecting your cables are exclusively copper, I’d recommend tinned copper for corrosion resistance and dielectric compatibility.

Additional Consideration #1: The cost of higher capacity cables and/or connections increases disproportionately to the derived benefits. Despite some of the other comments on this thread, my experience has been that there is a HUGE difference in the cost of 4 GA and 4/0 GA cable and lugs.

Additional Consideration #2: Availability of higher capacity cables and components. Guess what? That 4/0 GA lug only comes with a 1/2” hole and you want to connect it to a 1/4” lug on your battery separator. Yeah, you can probably make it fit by grinding down the edges, but…

Additional Consideration #3: Heavier cables and connectors are more difficult to handle. Not only are the cables themselves difficult to bend, route through firewalls and such, they are also more difficult to terminate. Prepare to invest in several different flavors of heavy-duty connector crimpers and/or heavy-duty soldering equipment to ensure you aren’t creating high-impedance connections that will totally overwhelm any power savings from the heavier cable.

Additional Consideration #4: Take a look at all of the components in your proposed design and make certain that they are properly matched for your requirements. Keep in mind that every time you route power through a set of relay contacts or circuit breaker, there is a set of metal contacts with a small, yet perceptible resistance, that is going to rob a finite percent of your electrical power. Quite frankly, if maximizing your overall power efficiency is your goal, I’d be more worried about the 1.5 A of power that is typically consumed by the energizing coil of your typical battery separator relay than the relatively insignificant line loss of your cable - scrap your SurePower 1315-200 for a Blue Sea 7622 magnetic switch.

Anyway, these are just my thoughts on your topic. I thought that at the very least, I would attempt to respond to each of your three questions.

[racer4]

OP here. Thank you for all the responses.

It sounds like the decision comes down to using large enough cable to minimize voltage drop and give good results without being so large that the cable is unnecessarily hard to work with or a waste of money.

100 amps over 6 feet with these sizes has a voltage drop of:

size, voltage drop, voltage drop %
1 AWG, .18, 1.5%
1/0, .15, 1.25%
2/0, .12, 1.0%

Where I am not clear is how much voltage drop I should choose that will give good results.

One more factor I forgot to say. The FW will also have a 200W solar panel factory installed (by Cedar Creek), which I am trying to have increased to 400W. Does that make a difference in choosing the cable size?