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Old 01-11-2014, 10:06 AM   #1
Sro
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About to wire TV to charge airstream

Just purchased a bambi 16! Very excited. I plan on using it for extensive boondocking.

I hope I'm choosing the right forum here. This is mainly about charging two 6V batteries from the TV. After reading several posts (thanks Yammer), I'm about to install the following:
  • 40A charging cable (#4AWG) from TV to airstream with 50A SMH connector and a 40A circuit breaker
  • 7 pin trailer connector with a 30A circuit breaker on 12V+
  • Running 4AWG cable for solar (which isn't yet installed).
  • Installing two 6V batteries (eventually upgrading to 4)

Here's the circuit diagram: https://www.dropbox.com/s/fht48aknqh...g-charging.png

Can anyone see any huge mistakes? Open questions:
  • I'm currently running two connectors to the airstream: a high-gauge cable (pos and ground) and the regular 7 pin connector. Should I scrap the high-amp SMH connector?
  • For faster recharging the alternator battery sense is running off the second 12V battery that's on the vehicle (this will often stay connected to the airstream and drain with the airstream). Bad idea?
  • Second battery will be connected to starter/primary battery when ignition is on so I figure even if the starter battery is low (due to no battery sense) the second battery should be able to start the vehicle.
  • Running lots of 4AWG cable (do I need it all?)
  • Eventually installing two PVL-68W solar panels (can I fit them on the roof? not sure...)
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Old 01-11-2014, 10:47 AM   #2
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Defender 90 eh? Cool!

If the Defender doesn't already have a heavy-duty alternator, you'll want one for the task you're setting for it. For the effort involved, figure up the cost of the solar before you decide between one or the other, since the solar will continue to charge without burning fuel, and will charge while you're towing (though of course will charge less on a gray days, etc.)
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Old 01-11-2014, 11:53 AM   #3
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First, this is my opinion only... So.

What are you going to be doing in the 16' Bambi which would require two sets of 6 volt batteries for power? I really can't imagine any load that would need that kind of reserve capacity.

Your diagram shows two small (68 watt) solar panels on the roof, one now, one future. That is about a 10 amp output maximum. It can easily be carried by the solar pre wire (if you have a newer Airstream) which is a #10 wire. A #4 wire is fantastic overkill. I am using the built in #10 solar pre wire on my 20' FC and two 100 watt panels and it works just fine.

Two batteries in the TV? Why?

# 4 charge lines are probably overkill also, unless you are running down the four 6 volt batteries very much, and want to charge them pronto.

One set of 6 volt golf cart batteries in series and a couple of 100 watt solar panels along with a MPPT charge controller will do you very well in all probability. If your Bambi does not have LED lighting, a change to that would be advisable. Also change your converter charger to a 3 stage "smart" charger if it has not already been done.

Remember, this is only my opinion and is worth what you paid for it.
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Old 01-11-2014, 12:12 PM   #4
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Thanks idroba! Helpful advice. My thoughts inline.

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Originally Posted by idroba View Post
What are you going to be doing in the 16' Bambi which would require two sets of 6 volt batteries for power? I really can't imagine any load that would need that kind of reserve capacity.
Boondocking weeks at a time. I'm also a computer engineer so I like my electronics. That said, I'll start with two 6V batteries and go from there.


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Originally Posted by idroba View Post
Your diagram shows two small (68 watt) solar panels on the roof, one now, one future. That is about a 10 amp output maximum. It can easily be carried by the solar pre wire (if you have a newer Airstream) which is a #10 wire. A #4 wire is fantastic overkill. I am using the built in #10 solar pre wire on my 20' FC and two 100 watt panels and it works just fine.
I heard you want the lowest resistance possible on the solar panels. That said, I didn't realize there was a pre-wire. I have a 2011, so I'm assuming I have the pre-wire?

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Two batteries in the TV? Why?
Already installed in the Defender for stuff like my winch.


Quote:
Originally Posted by idroba View Post
# 4 charge lines are probably overkill also, unless you are running down the four 6 volt batteries very much, and want to charge them pronto.

One set of 6 volt golf cart batteries in series and a couple of 100 watt solar panels along with a MPPT charge controller will do you very well in all probability.
Good to know. I might still run it since I like having power at my rear bumper (for stuff like a small rear winch).


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If your Bambi does not have LED lighting, a change to that would be advisable.
It does.

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Also change your converter charger to a 3 stage "smart" charger if it has not already been done.
Very interesting. I'm not sure what's installed yet. Do you recommend a model? I'm new here.
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Old 01-11-2014, 01:47 PM   #5
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I could not open your wiring diagram so I may be commenting on something that you have already considered, so I apologize if I am . Since you have indicated that you will be doing a substantial amount of boon docking, a good charge controller is most likely more important than an upgraded converter/charger. I rarely have shore power and my solar system seems to keep everything up perfectly. I leave the thing in "use" mode 100% of the time, and today, in the rain and fog, and having left the bathroom lights on by accident for two weeks, the controller showed the system at 100%. Jim
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Old 01-11-2014, 02:32 PM   #6
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Your Bambi probably has a solar pre wire, but since there have been some lower priced ones produced (the Sport) they may or may not have it. Either check with a dealer service department, Jackson Center service, or the manual if it is complete. My 2014 FC manual told where to find the wires. They are #10 and should be enough for up to a couple of hundred watts of panel. Mine are.

At 12 volts you do have to be careful about voltage drop on the solar panel wiring, but between the higher panel voltages used now and MPPT charge controllers (mine is a Blue Sea) the MPPT charge controller does some compensation for voltage drop. Again, with probably only space for 200 watts of panels on your 16' Bambi, I can't see over a 16 amp charge possible max anyway. Even with the length of wire involved, there will not be a significant voltage drop with a #10 solar pre wire.

If you are "boondocking for weeks at a time" I think a good solar system would be your best investment. You might also consider a small generator like a Honda 1000 inverter model. They only weigh 29#, are very quiet, use very little gas, and combined with a good 3 stage converter/charger will quickly recharge batteries if the sun does not do it. I am not a big fan of running any generator in boondocking situations, but an occasional use of one in daylight hours is not too bad.

I don't know what panel/charge controller is used in your 16' so I can't be sure what replacement 3 stage converter/charger to recommend. If it is a Paralax 7300 series, the one used in the larger trailers, a PD 4645 or 4655 would be a good replacement. If AS used a different system in your trailer, it might be something different.

I also like electronics but even new computers, MiFi modem/routers, and the like are pretty easy on batteries when used directly. I would recommend a small, high quality sine wave inverter with a low idle draw, and search mode, to keep your electronics which operate on 120 volts in service. The Morningstar 300 watt one comes to mind as it not only uses little power on standby, but has a 600 watt overload capacity for about 10 minutes. My FC 20 has a factory 1000 watt inverter, but it has an idle load of 1.75 amps which is way too high. I am going to add a Morningstar in the spring for my computer uses, and use the factory one only to run my toaster and microwave for a few minutes each day.
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Old 03-07-2014, 09:36 AM   #7
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SRO,
I agree with what's said above viz pre-wire, solar charge controller. I run four 6v golf cart batteries and love the capacity (rated 460ah). Four days with zero sun takes us to 62% of rated capacity, about as low as we want to go. Wired our two 125 watt panels in series to cut the current on prewire in half by doubling the voltage to nominal 24vdc.

Did change the Parallax 7355 converter/charger after it ruined second set of 12v group 24 Interstate batteries, I'm a slow learner sometimes. Bought the Progressive Dynamics Intellipower, we went with 9260 (60 amps), a slight increase in power over the 55 amp oem unit.

Finally, temporarily used a $30 410watt automotive inverter for charging stuff, and just ordered a 600 watt Xantrex Prowatt pure sine wave. We expect it will be far better, hopefully won't radiate hash on our ham radio signals, and will be more efficient to boot.

BTW, I enjoyed looking at your schematic. What did you draw it with? Nicely done.
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Old 03-07-2014, 11:29 AM   #8
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Quote:
Originally Posted by idroba View Post
First, this is my opinion only... So.

A #4 wire is fantastic overkill.
# 4 charge lines are probably overkill also, unless you are running down the four 6 volt batteries very much, and want to charge them pronto.

.
I second this. Having just pulled a new charge line for our camper, a #4 is huge, dang near as big as our umbilical. We went with an 8 for the charge line and a 10 for the brake and both are big compared to what was there originally. Not to mention that #4 is expensive.
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Old 03-13-2014, 10:32 PM   #9
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One note about your schematic: The negative from the solar panels should go to the charge controller's solar input negative. The positive and negative from the charge controller's battery output should go to the battery bank.

The PS-30M that you have listed has an optional battery voltage sense connection. Using the sense connections will allow the controller to compensate for voltage drop in the wire from the charge controller to the batteries. The sense connections are the two inner terminals under the battery symbol.
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