"Portable" battery in dual battery system (1 Viewer)

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woytovich

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I'm thinking I want a portable battery box, one of the ones with USB and other output options built-in. And I want to be able to move it between my (Yukon XL) tow vehicle, FJ60 and trailer (on the trailer it'll power the winch and some lights on an as-needed basis, no charging need there). I will also be able to use it as (heavy) portable 12v power source for a camping hot water system and other needs away from the truck(s).

So... I'm thinking Andersen connectors and some method to safely mount the box in each location. I'll be happy with a simple isolator to deal with charging. I'll want to be able to charge it in both the Yukon and the 60 and I'll want both to be able to function properly without the second battery.

To get this all to function on either 1 or 2 batteries I'll need to be able to get all of the items connected to the portable battery to run off of the primary... essentially bypassing the 2nd battery. Again: Andersen connectors I think.

Anyone out there have anything like this already...? I'm getting ready to draw it out and have no desire to reinvent the wheel if there are solutions available.

Thanks,
mark
 
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I would start by deciding how much power you really need stored in the battery box. If you want to power a winch it will need to be a fairly big battery.

Most of the time, smaller kits like you list are too small to be super useful and too expensive to be a reasonable thought. You mentioned running a winch so that's a huge load for any portable system. If you didn't need to run a winch that would allow you to down size your battery a lot.

But you also need to size it so it isn't too big or to heavy for one guy to move around. Plus you'll be moving it around so it will need to be "non-spillable" so that limits you pretty much to an AGM battery.

So I'd use the biggest AGM that you can easily pick up. An Odyssey 1500 battery is right about 50 pounds and might be just what you need. Heavy, but enough juice to matter. Mount it in a heavy duty tool box or Pelican box, with Andersen connectors to hook to your main system. Add other outputs as you see fit. Maybe an inverter inside the box if you need portable A/C. The ArcPac for $499 doesn't even have a battery with it, so look carefully at the ads. The Nat Luna for $560 also is minus the battery.

Getting enough power to it for charging while you drive will be a challenge. You need heavy cabling, fuses at both batteries and HD connectors like Anderson SB175s.

Do you have room to just install dual batteries in the Yukon? That might be easier and simpler.


Thinking about if I actually had to make one with with a big battery:

Main Battery<>fuse(150A)<>cable(2ga)<>ACR<>long cable to inside(2ga)<>SB175<>SB175<>Cable(2ga)<>Fuse<>#2Battery in box

That would work pretty well. THe ACR under the hood would assure the long inside lead is powered ONLY when a battery is hooked up to it, the wiring could handle large charging currents when the #2 battery is low and gets plugged in and the truck is running to charge it, and you'd have enough stored power to run anything you want. Install a voltmeter on the #2 battery to keep tabs on it and never let it go below say 12.2 volts without a recharge. Add USB charging ports, Cigarette type outlets, additional Anderson outlets, an inverter, basically anything you want that is 12 volt powered. It would easily hook to a solar system too.

But that's a lot of trouble, expense and complexity for 1 portable large battery. Things would get a lot easier if you didn't need to charge while driving, or could use a smaller battery. Let me restate, I would just install dual batteries in your Yukon AND your 60. Installing 2 dual battery systems will in the end be easier and more satisfactory than a large capacity portable system.
 
All great info, and pretty much what I just sketched out before dinner.

My situation is that I daily drive the Yukon and only wheel with the 60 a few days/year (12-15 if I'm lucky). And the winch I'll have on the trailer will be rarely used (I hope). A second battery just sitting in the 60 (on a battery tender) seems like a waste, and one for the trailer winch moreso.

It is true that I could get by as I have for 16 years with a single battery in each truck and this MAY largely be a mental exercise.

I was thinking to put some flavor of isolator in the box with Andersen connectors to connect it to either main battery (fuses etc of course). I'd have a mount spot in the trucks with heavy + & - cable running back. I'd look to mount the box behind the center console on the floor on both trucks. (to shorten the cable run)

I'd include a 120v Battery Tender connection so I could just leave it charging in the house when I knew I wasn't going to be using it for a while.

Question: If I wanted to limit the current that the battery box could draw during charging (to be able to use much lighter cable) is there a way to do that? If that was the in-vehicle charging method I'd use a high amp Andersen output connection to be able to run a winch or for a jump start or any high draw use. That would simplify the in-vehicle charging I think.
 
I was thinking to put some flavor of isolator in the box with Andersen connectors to connect it to either main battery (fuses etc of course).
There are electronic isolator units that will sense when the engine is charging, then connect up to allow charging of the isolated battery. Some will go both ways, like if you also had a solar panel charging your isolated battery. I know at least one has been mentioned on IH8MUD before but I can't remember it's name. I even mentioned one that was an electronic control on a mechanical relay that was one way, or both directions.
 
There are electronic isolator units that will sense when the engine is charging, then connect up to allow charging of the isolated battery. Some will go both ways, like if you also had a solar panel charging your isolated battery. I know at least one has been mentioned on IH8MUD before but I can't remember it's name.

You are describing an automatic charging relay = ACR. Super useful in dual battery applications. They don't limit current though, and thus the need for large cables. The large cabling serves 2 functions-it limits voltage drop and thus increases the speed of charging, and in situations where the #2 battery is low and accepting current quickly, you don't overload the wiring and blow the circuit protection.

Diode based isolators are a thing of the past. Avoid. Charging relays provide the same function, but without the associated voltage drop.
 
How much current can a battery draw during charging - ie when very discharged? The stock wire from the alternator to the battery on my 60 was pretty small (maybe 8g?)
 
That's a good question and you may have to measure and provide data. I have seen that some AGM batteries can accept C/2 charging rates so that's 50 amps for a 100 amp/hour battery. More standard batteries would be a bit less.

But if you measured and found that 20 amps was the max rate, then you could size your wires accordingly.

Regarding your FJ60, the alternator is only capable of 55 amps at best, so 8ga is about right. Even 10ga would likely do it.
 
No, because the main battery will also try to charge the #2 battery.
 
Unless it is isolated - which it would be... mostly because I wouldn't want running the winch/starter to try to draw back through the charge wire.

In my evil plan I would not have the 2nd battery hooked up in a typical dual battery arrangement (unless I CAN run heavy gauge cable that'll handle full winch/starting draw back to it). In order to use it in combination/instead of the main battery I would need to connect a heavy gauge jumper between the portable "kit" and the main harness. This would probably mean moving the "kit" closer to the front to make a shorter connection.

Another question I have is: what is the physically smallest battery I could use that would be able to run the truck winch for a reasonable time in an emergency situation. Is it just a matter of calculation using Amp Hours?
BatteryStuff Tools | Sizing a 12 Volt Battery to a Load Calculator

300a for 3 minutes = 56ah on an AGM battery
 
I was looking into something similar. I carry an inflatable boat with a trolling motor when were off exploring for those remote lakes. I'm looking at using the boat battery ,that's mounted in a Minnkota battery box that has 12-volt accessory plugs and manual reset circuit breakers built in, as a second battery in the Cruiser. I have a Blue Seas 7622 ML-ACR that I'm going to use as the backbone of the system. I can use it normally and have it isolate/charge the batteries automatically, manually combine the batteries for heavy loads or manually lock out the second battery completely.
 
I have seen that some AGM batteries can accept C/2 charging rates so that's 50 amps for a 100 amp/hour battery.
There are many lead acid AGM batteries that can take 4C charging rates and some that can take more. You just can't violate maximum voltage or temperature limits. You usually don't see AGMs made for the consumer market specified to those extremes, but you do see them on the industrial and military sides. As long as you don't overheat the terminals and cells, and don't go over the maximum charge voltage, they should be able to take high input and output currents. That is because their plate surface area is so huge. An interesting note on terminal temperature. At high currents, the + and - terminals will heat up. It is possible to melt them or the battery internal connections during prolonged high current discharge, like when winching.
 
What would the thinking be on using 2 smaller (golf cart?) batteries vs 1 larger? (thinking of this mostly for added flexibility in building the actual box to hold all of this)
 
I think cost would be the biggest issue going that way. It will cost more for the two batteries, and the additional battery cable. Weight may also be an issue.
 
I went for a similar system.

To fit a second battery under the hood of the BJ40 I'd need to remove my under-bonnet compressor so instead I wanted what I call a plug and play dual battery system.

It's got a VSR (Voltage Sensitive Relay - basically an automatic battery isolator) wired up in the engine bay and a power cable goes to a control box in the rear of the vehicle. This control box has an Anderson output and two merit plugs for running accessories from the rear of the vehicle rather than relying upon the cig socket and the trouble light socket in the front.

The heart of the system is a Kick Ass brand portable battery box with 2 x Anderson inputs, voltmeter, 2 x cig sockets, a merit socket (for running the fridge) and a double USB socket. Into this box goes a 130Ah AGM deep cycle battery. The battery box plugs into the control box using a 1m long Anderson fly lead.

The battery can be charged from the vehicle's alternator while driving, or from the 120 watt folding solar panels. Since space is at a premium in a Shorty Forty the battery box can be removed completely from the vehicle and used in camp as a solar generator.

I don't use much tech when I'm out on the track, so this setup only has to power -

A Waeco CF40 fridge freezer
Keep the Toughbook CF-19 batteries charged
Keep a Samsung Galaxy S5 phone charged - trail nav and camera
Run various 5v USB chargers for camera and phone batteries

For camp lighting I use Coleman fuel, candles or lamp oil, but this system should be able to easily run a whole lot of LED strip lights too.
 

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