Running a dual 12v battery setup in CMAX?

[SPL Tech]

I am interested in running a dual battery setup to run a fridge in the back of my car while it's parked. I travel a lot and live out of my car for extended periods. Anyway, if I use a relay/ silonoid to isolate the batteries, I am wondering if when I close the relay on the silonoid if the current draw from the dead battery will be too much for the inverter. I suspect that each night I will discharge the battery to about 30-40% power remaining, so when it comes time to charge it in the morning, I am not sure how much current it's going to pull. I know dead auto batteries can draw 100A after the car is jump started, which is a lot for the CMAX.

Any ideas? Ways to limit the current to the secondary battery? I was thinking of just going with a 20A or 40A relay, but I suspect what might happen is if the second battery tries to draw more current it will just overheat the relay vs actually limit current to the battery.

 

Edited January 11, 2015 by SPL Tech

[drdiesel1]

Why not use a static battery and charge it with a plug in charger. This car isn't equipped with a standard alternator.

You could plug the charger into the AUX outlet and charge it while you're driving. Otherwise, you'll need to get better

data on the 12V charging system to see if it can carry that extra load.

[SPL Tech]

Why not use a static battery and charge it with a plug in charger. This car isn't equipped with a standard alternator.

You could plug the charger into the AUX outlet and charge it while you're driving. Otherwise, you'll need to get better

data on the 12V charging system to see if it can carry that extra load.

I could do that, but a 10A battery charger would take all day to charge the battery. For a 500whr battery, you are looking at like five hours on a battery charger to fully charge it. I dont drive five hours everyday. When I am living out of my car there are days where I only drive a few miles. If I could run 40A to the battery, that would charge it quicker but not so quick that it damages the inverter.

 

Isint the inverter 2000W anyway? And 100% of the 12v power is supplied directly by the inverter, correct?

[ScubaDadMiami]

You can also look at getting highly efficient coolers. I spent several days at a time on the road while traveling in my C-MAX during this past summer, using just ordinary (Coleman) coolers with re-freezable ice packs inside. Even when I got to my destinations, I kept my food in the coolers, and I just rotated the freezer packs to re-freeze a set while the other stayed in the coolers. This was over the course of a month and a half, and it worked very well.

 

Instead of freezer packs that require this re-freezing, you can also instead just stop at convenience stores and supermarkets to pick up ice along the road. Again, I used ordinary coolers instead of the more expensive coolers that are said to keep food cold for much longer than my inexpensive version, but between the better coolers and stopping for ice (if you can't use the re-freezable packs), you can go for months on end like this without any problems. The only issue with using ice is that you will need to take measures to keep the ice from slowly melting and getting your food wet, but that is easily done.

[SPL Tech]

Yea, the cooler wont work for me. I spend 9+ months on the road, I dont want to get ice every two days for that long. The dual 12v battery system seems to be the only way to go.

[SnowStorm]

Yea, the cooler wont work for me. I spend 9+ months on the road, I dont want to get ice every two days for that long. The dual 12v battery system seems to be the only way to go.

Sounds like you need a battery charger that takes 12 VDC (nominal) in and steps it up high enough to charge the second battery.  Something like this item:

http://www.powerstream.com/pst-pb1108.htm

 

I have no association with the company and haven't used the charger but something like this is what I would try before ever attempting any direct connection (too many potential problems).  This unit has galvanic isolation which is a plus.  At 8 amps you can charge a 500 watt-hour battery in about 5 hours.  They say you can use two in parallel for twice the charge rate.  And there are probably others out there with higher output current capability.  Hope you find something that works.  I went "out west" for a month using ice and it was indeed a hassle.  Tried dry ice once and it made the fruit taste funny!

[drdiesel1]

The C-Max uses a control module to setup battery charging. It has a data input to properly

charge the 12V battery. It will not automagically accept the second battery and keep the system

properly charged. You might run into a problem without being able to properly setup for the added

load. I don't know the limits of the systems input parameters, but you'll need an IDS to change anything.

Edited February 4, 2015 by drdiesel1

[Marc Smith]

i guess depending on where you park your car...

 

why not just plug the fridge into a house outlet at night,  and then into the cmax outlet in the morning...

 

yeah it might be a pita,  but  it beats risking damage to the cars electrical system...

 

unless you could fit a deep cycle battery 12v battery into the car and keep a single battery.

 

the problem with the inverter, IMO  is that  you are loosing efficiency in the transfer from 12v to 110.  why not just get a 12v fridge/cooler  and ditch the inverter...

 

I'm assuming you are thinking about a compressorless unit...

[fbov]

Sounds like you need a battery charger that takes 12 VDC (nominal) in and steps it up high enough to charge the second battery.  Something like this item:

http://www.powerstream.com/pst-pb1108.htm...

+1

 

The plug in the console is switched with the ignition, the one in the trunk is not, so you have easily accessible options. The AC plug is also switched, I believe, but at 150W, you could get a reasonable charging current. Seems to me you need an additional current source, like solar if you can't plug in.

 

Don't discount the performance of the latest generation of coolers. Block ice would easily last a week or more if the cooler's in shade. Conversely, a newer active cooler may be just as well insulated.

 

Have fun,

Frank

[scottwood2]

You might want to look at marine refrigerators.  They can cost more but can be very efficient at the using battery power.  Still does not solve your battery problem but you might not need to charge as often.  The standard electric car coolers eat up power pretty good. 

[Adrian_L]

My camper fridge doesn't work very well on 12 volt, but is amazing on LPG--and uses very little gas.   You might be able to find a small marine ammonia fridge that runs off LPG--attach it to a small cylinder and it would go for days.  

 

I remember seeing one a few years ago that ran on 120v, lpg or 12v and it was the size of a large cooler.

Edited February 4, 2015 by Adrian_L

[SPL Tech]

I am not using an electric cooler, I am using a legit, $800 12V freezer. It doesn’t get any more electrically efficient than that. Coolers dont work. It gets over 140F in a car in the summer, even with the windows cracked. Ice will evaporate in 48 hours in a Yeti in that temp.  Colemans wont even last a day at that temp. Plugging the freezer into a house is impossible--car power only. Everything must come from the car, no external sources. I live in the car. It’s my mobil house. I am sure this has been done before, it's just figuring it out.

 

I wonder if I could use a direct connect and wire a 100W lightbulb in series with the two batteries. The lightbulb would act as a variable resistor and limit current to the second battery without limiting the voltage.

 

Another option might be to use a 40A battery charger. I have a 400W power inverter, so I can use that with a battery charger if needed. Battery chargers are cheap on eBay.

 

I have considered solar as well. However, 100W solar panels are massive and it would be hard to mount something like that on the roof. I considered getting a 50W panel and mounting it in the sunroof, but it seems the glass is tinted from the factory so I suspect it wouldent work well.

Edited February 4, 2015 by SPL Tech

[Adrian_L]

Electrical efficiency?  Really?  I'm guessing that thing probably pulls 6 amps of DC power. 

 

Let's say you have two 6v Trojan T105s, a pretty common choice for RV deep cycles (and 120 pounds in weight).  You can only discharge them 50% to ensure they stay healthy.  So basically you're looking at 900 minutes for a 6 amp drain.   That's 15 hours before you have to charge those big boys back up to full capacity.   Did I mention those batteries are big? 10"(l) x 7"(w) x 11"(h) 

 

A quart of LPG will keep a Dometic fridge/freezer running for a week or more. 

 

Also, it makes no sense to run a 12 volt appliance from a power inverter when you can simply tap into the coach battery/car's 12 volt system directly.  Why add an unneccessary step when your inverter is probably only 85% efficient?

Edited February 5, 2015 by Adrian_L

[SPL Tech]

Also, it makes no sense to run a 12 volt appliance from a power inverter when you can simply tap into the coach battery/car's 12 volt system directly.  Why add an unneccessary step when your inverter is probably only 85% efficient?

That is what I would like to do, but multiple people in here so far recommended against it. I dont want to deal with solar if I can just charge the battery with the car. My idea so far has been to just wire the second battery in parallel with the first using a 50A relay in between, triggered to turn on when the car is in the ready mode. Also, running a LPG freezer in an enclosed, unattended car is beyond a bad idea. It’s probably even illegal. Those freezers must be used in a vented area and they must be attended to 24/7, same as a LPG stove. Also, the freezer draws 3A, and it only has a duty cycle of 50% at most, so you are looking at maybe 20w/hr on a really hot day. I dont need anything as large as the Trojan T105. A simple 40Ah 12v battery is sufficient as I am not going to go longer than 12 hours without driving the car.

Edited February 5, 2015 by SPL Tech

[drdiesel1]

That is what I would like to do, but multiple people in here so far recommended against it. I dont want to deal with solar if I can just charge the battery with the car. My idea so far has been to just wire the second battery in parallel with the first using a 50A relay in between, triggered to turn on when the car is in the ready mode. Also, running a LPG freezer in an enclosed, unattended car is beyond a bad idea. It’s probably even illegal. Those freezers must be used in a vented area and they must be attended to 24/7, same as a LPG stove. Also, the freezer draws 3A, and it only has a duty cycle of 50% at most, so you are looking at maybe 20w/hr on a really hot day. I dont need anything as large as the Trojan T105. A simple 40Ah 12v battery is sufficient as I am not going to go longer than 12 hours without driving the car.

Do the math. Have a local dealer see what the BECM has for rating inputs. If the numbers work, you can have them adjust

it to what's required and you're done.

[Adrian_L]

That is what I would like to do, but multiple people in here so far recommended against it. I dont want to deal with solar if I can just charge the battery with the car. My idea so far has been to just wire the second battery in parallel with the first using a 50A relay in between, triggered to turn on when the car is in the ready mode. Also, running a LPG freezer in an enclosed, unattended car is beyond a bad idea. It’s probably even illegal. Those freezers must be used in a vented area and they must be attended to 24/7, same as a LPG stove. Also, the freezer draws 3A, and it only has a duty cycle of 50% at most, so you are looking at maybe 20w/hr on a really hot day. I dont need anything as large as the Trojan T105. A simple 40Ah 12v battery is sufficient as I am not going to go longer than 12 hours without driving the car.

 

Exactly.  Wire the second battery in parallel and the charging system will just see it as one huge 12 volt.  I'm a huge fan of the Cole Hersee smart isolator because it will not connect/engage the batteries unless the starting battery is strong.   But folks with twin battery setups have been using non-smart relays for years (they're about $20--RV dual battery "relay")  and they simply connect the batteries when the car is on and disconnect when it is off.  I'd wire in an on/off switch too.

 

3 amps is pretty impressive for a 12v freezer. 

[drdiesel1]

You should read this before adding a battery to this car.

 

Your vehicle is equipped with a Motorcraft® maintenance-free battery which normally does not require additional water during its life of service.

Note:  If your battery has a cover/shield, make sure it is reinstalled after the battery has been cleaned or replaced.

Note:  See an authorized dealer for low voltage battery access, testing, or replacement.

When a low voltage battery replacement is necessary, see an authorized dealer to replace the low voltage battery with a Ford recommended replacement low voltage battery that matches the electrical requirements of the vehicle.

To ensure proper operation of the battery management system (BMS), do not allow a technician to connect any electrical device ground connection directly to the low voltage battery negative post. A connection at the low voltage battery negative post can cause inaccurate measurements of the battery condition and potential incorrect system operation.

Note:  If a person adds electrical or electronic accessories or components to the vehicle, the accessories or components may adversely affect the low voltage battery performance and durability and may also affect the performance of other electrical systems in the vehicle.

For longer, trouble-free operation, keep the top of the battery clean and dry. Also, make certain the battery cables are always tightly fastened to the battery terminals.

If you see any corrosion on the battery or terminals, remove the cables from the terminals and clean with a wire brush. You can neutralize the acid with a solution of baking soda and water.

When a battery replacement is required, the battery should only be replaced with a Ford recommended replacement battery that matches the electrical requirements of the vehicle.

Because your vehicle’s engine is electronically-controlled by a computer, some engine control settings are maintained by power from the low voltage battery. Some engine computer settings, like the idle trim and fuel trim strategy, optimize the driveability and performance of the engine. Some other computer settings, like the clock and radio station presets, are also maintained in memory by power from the low voltage battery. When a technician disconnects and connects the low voltage battery, these settings are erased. Complete the following procedure in order to restore the settings:

1. With the vehicle at a complete stop, set the parking brake.

1. Shift the transmission into P.

1. Turn off all accessories.

1. Step on the brake pedal and start the vehicle.

1. Run the engine until it reaches normal operating temperature. While the engine is warming up, complete the following: Reset the clock. See General Information.  Reset the power windows bounce-back feature. See Power Windows.  Reset the radio station presets. See General Information. 

1. Allow the engine to idle for at least one minute. If the engine turns off, step on the accelerator to start the engine.

1. While the engine is running, step on the brake pedal and shift the transmission to N.

1. Allow the engine to run for at least one minute by pressing on the accelerator pedal.

1. Drive the vehicle at least 10 miles (16 kilometers) to completely relearn the idle and fuel trim strategy.

Note:  If you do not allow the engine to relearn the idle and fuel trim strategy, the idle quality of your vehicle may be adversely affected until the engine computer eventually relearns the idle trim and fuel trim strategy.

Note:  Always dispose of automotive batteries in a responsible manner. Follow your local authorized standards for disposal. Call your local authorized recycling center to find out more about recycling automotive batteries.

Note:  It is recommended that the negative battery cable terminal be disconnected from the battery if you plan to store your vehicle for an extended period of time.

Edited February 6, 2015 by drdiesel1

[ptjones]

If you use your jumper battery to connect to positive and negative post under the hood you don't have to reset all your settings when you are working on the 12v battery. :)

 

Paul

[drdiesel1]

If you use your jumper battery to connect to positive and negative post under the hood you don't have to reset all your settings when you are working on the 12v battery. :)

 

Paul

Or you can get an OBDII plug that connects to a jumper if you don't wanna do that ;)