Ram Promaster Forum banner

1 - 20 of 20 Posts

·
Registered
Joined
·
7 Posts
Discussion Starter · #1 ·
I have a Promaster and I want to add a house battery that will power the lights etc. that I will add. I want to be able to charge this battery from the vehicle alternator. Is there a wire that runs to the rear of the PM that provides power to charge the battery in a towed trailer that I can splice into for this purpose?
 

·
Super Moderator
Joined
·
10,679 Posts
To get a decent charging rate I think you will want to use a heavy cable for the POS side at least. A lot if people use a 2/0 or 4/0. Plus you want to keep it short, not long and add an isolator to prevent discharging the starter battery. There are some very good, informative write ups here if you do a search.
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #3 ·
Thanks Keeponvaning. I did look at a bunch of posts and concluded that I will use from 4 gauge to 10 gauge (I read from someone herein that the wire size I need is 10 gauge wire running from my vehicle battery to my house battery, seems a little small?) The run will probably be 10 feet. I think I will use a Voltage Sensing Relay to isolate the batteries and a fuze at each battery. Can anyone provide me suggestions for my plan? I like the idea of a Voltage Sensing Relay instead of a solenoid because then I don't need to use an ignition switched source.
 

·
Premium Member
Joined
·
8,838 Posts
Minimum of 4AGW but 2/0 would be even better as KOV says. It needs to carry up to 170 amps as reported by one poster. Mine is fuzed at 80 amps and 4AGW. The fuze has never blown but then I have never had a really flat set of house batteries! Solar charges my batteries unless it refuses to shine.
 

·
Registered
2014-159 HR in CT
Joined
·
3,709 Posts
I would recommend a Wirthco Battery Doctor as your isolator. Works great in my PM.

Not sure where you plan on putting the aux battery(s), but closer to the van battery is better. I put the Wirthco unit on a board mounbted to the back of my driver seat, then fed the batteries in my couch, about 3 feet behind the driver seat.

Ed
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #6 ·
Taylor said the following in a previous post:

"For years, I have run a 10 gauge cable from the front to the back, with a fuse or breaker to protect in case of too much current being drawn. Never a problem. Never even popped a fuse. And this is extensive daily use, many times running the rears down to an unuseable voltage, starting the engine to recharge, and even continuing to use the inverter while charging"

Seems like if the house batteries are completely dead and the alternator is able to put out 180 amps, and a 10 gauge wire is rated for 30 amps why doesn't Taylor's Breaker blow. What am I missing??
 

·
Premium Member
Joined
·
8,838 Posts
The house battery has internal resistance which prevents a large current from passing through at the 14+- voltage the alternator puts out. Other battery types have less internal resistance and will see much higher current. BTW if you use 10 guage wire and fuze it for 30-40 amps the fuze will protect the wire and it will not burn out the wire. If you fuze it for 100 amps the wire will protect the fuze. Enough said? 4AGW and 50-80 amp fuze or 2/0 and 100-125 amp fuze! Some batteries loose internal resistance as they age so his experiment may not be over. Taylor is a smart guy and will be fine. You need to do your research as well as getting free advice from us. Google wire size, voltage loss, and current, then make your decision. I don't understand why you wouldn't just go for a larger wire as it will probably not cost you $10 more. Not a big issue money-wise but too small a wire is a big deal. Best to you.
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #8 ·
I appreciate all the help I have received and think I have what I want to do. Please correct me if I'm wrong. The run will be 6'. I will use a 2 AWG wire for the positive side and use a chassis ground for the negative side. I will put a 100 amp breaker in the line at the house battery and the vehicle battery. I will put a Voltage Sensing Relay in the house battery box to isolate the two batteries.
 

·
Premium Member
2014, 138WB, High Roof, Gas, SW MT
Joined
·
2,126 Posts
Hi,
Another thing to keep in mind is that you don't want to damage the house battery with an excessive charging rate. I'd look up what the manufacturer of your battery recommends for a maximum charging rate and then put a fuse or breaker on the wire from the van battery/alternator to the house battery that is not much above that.

I have two 220 amp-hr 6 volt golf care batteries hooked in series. Trojan Battery recommends not more than 38 amps charging current for this setup. I put in a 50 amp breaker just so as to be sure to know if the battery charging current was too high. Its hard to predict what it will come out as it depends on the alternator/regulator characteristics and the internal resistance of the battery. Another way to check it would be to just put an amp meter in the wire or use a clamp on DC amp meter to measure the current.

In my mind, there is no advantage to using wires that support charging currents in excess of what the battery manufacturer recommends for your battery as long as you have the fuse or breaker to protect the wire (and your house battery).

This voltage drop table will tell you what size wire so that you don't exceed a 2% voltage drop in the wire: http://www.solarseller.com/dc_wire_loss_chart___.htm
For example, if you max charging current is 40 amps, a 4 gage wire will give you 2% voltage for a wire length of 9 ft.

Just as a side issue, the wire from the van battery/alternator to the house battery should have fuses or breakers near each end -- that is, one near the van battery and another near the house battery. This is because you have a very large current source (the batteries) on both ends.

Gary
 

·
Registered
Joined
·
2,106 Posts
Taylor said the following in a previous post:

"For years, I have run a 10 gauge cable from the front to the back, with a fuse or breaker to protect in case of too much current being drawn. Never a problem. Never even popped a fuse. And this is extensive daily use, many times running the rears down to an unuseable voltage, starting the engine to recharge, and even continuing to use the inverter while charging"

Seems like if the house batteries are completely dead and the alternator is able to put out 180 amps, and a 10 gauge wire is rated for 30 amps why doesn't Taylor's Breaker blow. What am I missing??
I think what you may be missing, which is also not discussed often enough, is that while the battery has resistance, a smaller wire does also which limits current to some maximum amount; but that depends greatly on its length.

First of all, I've never put a charger on a dead battery and have it take anything close to 180 Amps. Dead batteries don't take much current in my experience. Even very large tractor batteries started accepting current slowly and then picked up the pace a little.

More realistically, and getting back on topic, let's say you have a battery at 11 Volts and it is connected to an alternator putting out 14 Volts. If you have very short and large wiring, current will essentially be limited by the resistance of the battery. Let's "assume" a battery that would take 100 Amps under those conditions.

Now, instead of connecting the battery to alternator with a short and large cable/wire that has next to no resistance, let's assume you connect it with 10 gauge cable a mile long. In this case the resistance of the battery and cable are in series, which would limit current to much under 100 Amps.

If the cable is long enough, it will limit the current enough so that it won't get hot and burn out. Unfortunately, it will take forever to charge the battery.

On a real basis, as the cable is made shorter (say, less than 15 feet to back of motorhome) its resistance will be much less, which will allow more current to flow. That in turn will charge battery faster but may overheat cable due to higher current (although a proper fuse would protect it).

To summarize, the system you described will be somewhat self regulating because as current increases, the voltage drop due to resistance in wiring will also increase, which "effectively" leaves less between alternator and battery to push higher current through battery.

Some smaller inverter/chargers come with only 20 Amps of charging capacity, so it's not necessary in every case to charge at alternator maximum rating of 180 Amps -- or whatever it is.


I'm not promoting using smaller wires or cables. Mostly because it's too difficult to calculate in advance what will happen -- but it is possible. The above is my attempt to answer your question on how smaller wires could work without blowing a fuse.
 

·
Premium Member
Joined
·
8,838 Posts
johnr9q,
Your last post sounds fine, it will work, don't forget the fuzes that GaryBIS suggests, sized for your wire. Get'er done!
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #12 ·
I'm not sure what isolator to use. Someone herein suggested the "Wirthco Battery Doctor" I looked that up and not sure if I need to hook it up to the ignition switch. I like the Voltage Sensing Relay idea: Keyline Iso-Pro-140 http://www.keylinechargers.com/ because it doesn't need to be hooked to the ignition switch. It uses voltage sensing technology. Another option is: http://www.powerstream.com/battery-isolator.htm What are others opinions?
 

·
Registered
Joined
·
174 Posts
Go with the Wirthco Battery Doctor (WBD), it is foolishly simple to hook up. It is a smart isolator with a float button, so if you ever drain your main battery you can float both batteries together to get your main back up to starting potential. You only run 1 wire, your 12-volt+ from main battery to the WBD then another 12-volt+ to the second battery. It has a pig tail ground that you can frame mount anywhere.

I have always looked at sizing wire as a safety protocol. Once when I was a wee-little lad I had a Jeep Cherokee with 4 Hella lights on the roof. In those days there were no LED lights so these things sucked some power. I hooked the 4 up with 10awg wire, thinking that was enough. I dont remember what my fuse situation was but the wiring got so hot it started to melt. I overloaded the wiring and could have caught fire. Lesson learned that day to do more research. And today, I always care a fire extinguisher in my vehicle too.

I mounted my battery under my seat with 2-awg wire, at that run it is plenty. Used a Battery Doctor which is self fused but also added a re-settable breaker, so if I ever need to work on one of the batteries I can easily separate them and not fuse with a fuse. Also, if something trips and I figure it out why, I can simply reset the breaker. This is the breaker I used: WirthCo 31206 Battery Doctor 150 Amp Manual and Switchable Reset Circuit Breaker with Terminal Cover

There is a saying I tell myself, cheap people pay twice. I have made that mistake a couple of times with my van. What little money I have extra to spend on it, I always make sure to buy what is best for the long term. Just my 2-cents.
 

·
Super Moderator
Joined
·
10,679 Posts
I don't know anything about the others but this is the one I used and it's worked perfectly for two years.



You should also consider a disconnect switch. This is the one I used but you can find simpler ones for as low as $10-15.

[ame]http://www.amazon.com/Blue-Sea-Switch-Batt-Mini/dp/B005FD2PPU?ie=UTF8&keywords=Blue%20seas%20disconnect%20switch&qid=1465316573&ref_=sr_1_9&sr=8-9[/ame]
 

·
Premium Member
Joined
·
8,838 Posts
I looked at your choice and I like it.
Mine was so simple a caveman could use it- want to charge the batteries all the time, no problem just install it w/o a switch, want to charge the batteries when you know they need it, just insert a switch in the actuator circuit and when the van starts it charges, want to never charge the house battery from the van (my usual choice) switch off the switch!. Yup caveman simple!
KOV is right about a disconnect I used this one: [ame]http://www.amazon.com/Camper-Battery-Isolator-Disconnect-Switch/dp/B014ODGUXY?ie=UTF8&keywords=battery%20disconnect&qid=1465325033&ref_=sr_1_3&s=car&sr=1-3[/ame]
It is conneced between my house battery and the chasis ground effectively disconnecting the house battery from everything JIC!!
All this stuff is simple, has worked in RVs for years and Cheap. You be the judge its you camper and your money.
 

·
Registered
Joined
·
2,106 Posts
...cut....

want to never charge the house battery from the van (my usual choice) switch off the switch!. Yup caveman simple!

....cut....
If not from the van, from what source do you usually charge? For how long, how often, etc.?

Having a stand-alone system intrigues me, but I usually think in terms of requiring a second alternator. Sounds like you usually accomplish the same without need for a second alternator?
 

·
Premium Member
Joined
·
8,838 Posts
200 watts of solar- Cost about $550, see my build thread for a spreadsheet with the sources and costs. I fail to see why another source is required unless nature fails you which will happen but seldom. I have about 10 years experience with a windplant for house power and if the system is sized right you can get to 85-90% Solar is better than wind power!
I have camped and traveled about 3 months of the past 10 months 45 days to three weeks at a time. I have charged from the campground's 110 volt one evening. I have connected the alternator through my solenoid two ither times after two days with little or no sun (pouring rain actually! My solar will have my 120 A-H battery set fully charged by 11:00 - 11:30 AM on a sunny day, by 2:30 PM on cloudy days. I run a 12 volt refrigerator all the time, LED lights, Fantastic Vent when needed, 14 volt TV in the evenings, charger for my laptop, phone, tablet.
 

·
Super Moderator
Joined
·
10,679 Posts
RD there is an abundance of free hot air out there! Perhaps it could be harnessed to charge the house batteries?
 

·
Registered
Joined
·
167 Posts
On my van I ordered back extra-power outlet +12v. It does work only with running motor !!!! =BAD.
I took standard ~120volts power cord 12 gages it has 3 wires inside, and run "My-Way" +12v cable to a back of a van. I use all 3 cable wires in parallel so TOTALY after I've got 12:3=4 Gages wire.
For a (-) wire I used chassis.
 

·
Premium Member
Joined
·
8,838 Posts
1 - 20 of 20 Posts
Top