| Author | Message | ||
| woody48348 (66.82.48.141) Rating: N/A |
I need some advise please. I want to charge my house batteries from my 12VDC 300AMP Alternator when on the road. So, I bought a 300AMP isolator from Wrico, which will be mounted next to the bus batteries in the back of my Eagle. The house batteries are located in the front bay. Now to the question. What is the minimum size wire I can run the 30 feet. I can't imagine the house batteries will ever draw the full 300 amps, or even 200 amps, but safety is the most important issue. I have a spare conduit that runs from the battery compartment to the front bay that was used to run DC power to a radio box located in the bay. Is it advisable run my wire through this conduit, or would this greatly effect the current capability due to possible heat build-up? Is 2/0 welding cable large enough? | ||
| FAST FRED (63.215.231.101) Rating: N/A |
The house batts will draw about 20% of their total capacity during the heaviest period of recharging. ON a GM there is wiring in place to operate 2, 80-A blowers that would be used. Is there EXISTING quality wiring already in your coach that could just be converted? FAST FRED | ||
| woody48348 (66.82.48.141) Rating: N/A |
The existing wires that run through the conduit I mentioned, go to a previously installed radio box. These wires are two 6AWG, or maybe 8AWG. They are breakered at 40amps back by the bus batteries. I have six Trojan 31XHS batteries for my house, rated at 130AH each. If I multiply this number by 6; then multiply by .2, I arrive at 156Amps. A 6AWG wire, 30ft long can safely handle 70amps, with minimal voltage drop, so can I assume two 6AWG wires tied to the same point front and back will handle 140 amps? With this calculation, I am 16amps short. Is this calculation correct? | ||
| Geoff (64.1.0.62)
Rating: N/A |
Go to a welding supply store and buy as many feet of #4 welding cable as you need, along with solder type lugs (also available in auto parts stores). These are the best cables you can use and the price is right, you just have to put the ends on-- write back if you are not sure how to solder the ends on. --Geoff '82 RTS CA | ||
| jmaxwell (66.42.92.5) Rating: N/A |
Ure cable to the batteries must be capable of the Max . load encountered. U don't mention which inverter u are going with, but simply put, the battery cables need to be sized to equal the battery to inverter cabling, and that pretty much eliminates all these line voltage wire guages mentioned above. It appears that u have a ampacity chart that I have never seen; I have never seen #6 rated for 70 amp (even thhn is only rated to 55 amps in all charts that I have seen). I would not consider anything less than #1 and preferably 2/0, a common welding cable size. Your 30 ft. run also exceeds most specs., which requires even heavier wire on your application. Don't waste time and money on under-sized cabling. This ain't your Daddy's Oldsmobile electrical system and it definitely requires "big" cabling. Forget the #6 and #4 stuff and start looking toward the 0 guages. | ||
| Jojo Colina (Du1jec) (209.75.20.72)
Rating: N/A |
Remeber when putting on the terminals. Crimp and solder or crimp only. Soldering alone does not give the joint the mechanical strength to withstand the vibrations it will see. With welding cable even 4/0 is not difficult to work with. I used 2/0 and 4/0 welding cable for all my inverter/battery wiring. Jojo | ||
| Phil Pellowski (Viater) (164.58.86.161)
Rating: N/A |
I'd like to piggy-back onto this question. I also have a 300 amp Isolator that I'd like to use to charge my house batteries with my 300A alternator. My question deals with the external voltage regulator. It is connected to my coach batteries so it controls how much current the alternator puts out. Won't this effect my attempts to charge my house batteries? Phil PD4106-1726 | ||
| Driving Miss Lazy (66.190.119.82) Rating: N/A |
#6 wire rated for 70 amps is for conductors that have a temperature rating of 85 or 90 degree C. The NEC lists conductors rated at 250 degree C. that has an ampacity of 120 amps. I suspect this would be very expensive wire and is listed as type TFE. Richard | ||
| jmaxwell (66.42.92.19) Rating: N/A |
Phil P: Your Delco VR does not control the amperage output of the alternator; that is an internal function of the alternator; it is self regulating in respect to amperage. The VR only controls the voltage output. Your house batteries will charge to the voltage level of the regulator setting which is adjustable via a 1k trim pot in the regulator, accessible thru a small screw cap. The trim pot is very sensitive and only requires very minute movement to affect a voltage change. You can also accomplish the same thing by using a heavy duty continuous duty solenoid, activated off the R terminal of the alternator for charging the house batteries while running. U might find this to be a cheaper and more reliable means than the FET isolators. | ||
| Henry R. Bergman, Jr. (Henryofcj) (63.224.197.10)
Rating: N/A |
All of the above answers are great and really should help you out. Here is some more that is a little bit more practical and not all that $expensive$ too. The key is sizing 12 VCD cable is the lower the precentage of voltage loss, the better. Most of the available printed charts, values, recommendations and stuff usually (not always)... Assume around a 5% voltage loss between one end and the other. FIVE PERCENTAGE VOLTAGE LOSS IS TOO MUCH!. By the time you are done with the wiring, you have 5 percentaged yourself into a corner..... And end up with a marginal system. This happened to us (me) years ago when we started the solar homestead cabin in SW OR. We just went with that was recommended and found out things really did not work well. The key is sizing DC cable is to aim for a minimum of a ONE PERCENT TO A ONE AND ONE HALF PERCENT VOLTAGE LOSS AND MORE MORE! One of the neatest and best (and honest) DC wiring charts I ever saw was in an old issue of Home Power Magazine. The formula for figuring voltage loss in wiring runs was easy to understand and worked with whatever voltage one would want to employ. Also worked with AC circuits also. Anyway, to make a long post even longer, we rewired the cabin's DC side with much heavier cable and the system ( M51 35 cell PV panels and NiCads) worked just great. Maybe some of us Bus Nuts may have access to the older issues of Home Power Magazine and be able to answer your specific questions. Heavy multi-strand FLEXIBLE welding cable is fairly cheap.... Compared to the entire cost of a conversion. Go with the heavy cable and your DC system will work well. Also important are the type and make of the sodderless crimped connections on the cable. Little things within the circuits will kill you with voltage losses that may not be understood. The less connections the better. One piece cable runs are better than multiple splices. Also understand that a lot of the cheap and available peanut connectors and such are NOT designed for high amperage, low voltage connections. Anyway, good luck. Henry of CJ | ||
| David Anderson (168.215.176.98) Rating: N/A |
I bought 28 feet of 4/0 welding cable with the ends installed from Wrico for $3.58/ft. I have a 350 amp Niehoff alternator that merges with the house batteries by an oil pressure switch. The continuous duty solenoid can't take the starter amps, thus the need to disengauge until engine oil pressure rises. I also installed a 300 amp fuse at both ends because both cables are always powered up. I can run my front Coleman rooftop off the 2500 watt inverter from alternator power going down the road. One thing I found out in my installation that puzzled me was, that when the solenoid coil was powered by the house batteries it didn't work correctly when the oil pressure switch sought ground on the engine. It slowly melted the inline fuse (10 amp) I put on the coil wire. I switched the solenoid coil positive lead wire to get its power from the bus starting batteries, then all has worked well since. It must of had something to do with the grounding. David Anderson | ||
| R.C.Bishop (128.123.221.138)
Rating: N/A |
Good post Henry. Thanx for taking the time. Now continue.....  . RCB | ||
| Driving Miss Lazy (66.190.119.82) Rating: N/A |
David, I would suspect your problem is the lack of a good ground between the bus chassis and the engine. I assume your house battery ground is to the chassis of the bus and the starting battery ground is connected directly to the engine. Make sure there is a heavy duty strap between chassis and engine. BTW, did you do any good on the battery tester? Richard | ||
| jmaxwell (66.42.92.27) Rating: N/A |
Henry: I happen to find the chart u mentioned; same one I used. Here it is in condensed form VDI= (Amps X Feet) divided by (%Voltage Drop Sought X Voltage) Where VDI is the Voltage Drop Index Feet is the one way wire distance % Volt Drop is any whole number that is acceptable but 1-2 is preferable and never, never, more than 5 To apply the final result of the formula refer to the chart (I eliminated all wire sizes below #2 as they are not practical to use) VDI# / Wire Guage /Ampacity 31 2 130 49 0 170 62 00 195 78 000 225 99 0000 260 If your VDI # is more than 10% above the VDI# listed, step up to the next size wire. As can be seen, smaller wires are not really usable from an amperage capacity standpoint. Like the comment on the chart points out, the purpose is to get power where u need it, not to heat wire. | ||
| David Anderson (66.90.194.110) Rating: N/A |
Richard, Haven't had time to find the battery tester. I've been upside down all week installing the Webasto system as you read in my other post. I'll check later when time permits. I did get my shocks installed Saturday, except for the Bogies. The wheels have to come off for that. I can't wait to drive her to see the ride difference. David Anderson | ||
| Bus Jock (198.81.26.174)
Rating: N/A |
I will strongly agree with the requirement to minimize voltage drop. NEVER use the ampacity ratings that are put out by the NEC. They are for 120 volts, and a few volts there are no sweat. They are to keep you from burning down the house. Not worth a hoot at 12 volts! At 250 amps (running the inverter or charging dead batts) the 4/0 cable for 30 feet is marginal at 0.76 volts drop. with that much drop you will have some trouble charging your battery properly. With only 12 volts to start with I would like to see the VD about 0.1 to 0.2 volts (about 1 to 2%) 4/0 is is the minimum size I would recommend. Remember that each 3 wire gauges doubles the cross section, therefore two each 2/0 has more ampacity than a single 4/0 and is often easier to install. I have posted ampacity worksheets on my website, and can email the Excel file to make it work for any desired run and current. at: www.purplebear.com/busnuts Jock Fugitt |