Second 12v camping battery and charging circuit

It's really not as complicated as you guys are making it out to be! Boom $120 and the problem is solved. Plus it's replaces the cigarette lighter outlet it uses with another one. Has a light, an air compressor, 2 usb outlets and a built in inverter. The Prius cigarette lighter charges it at an acceptable rate and as soon as the car is turned off so is the power to and from the pack and the lighter outlet... I run a cpap, oxygen concentrator, and a nebulizer, heating pad, and an electric blanket off of mine. Plus I power all my electronics with it as well. A hotspot, tablet, phone, bluetooth speaker, etc... I use the other cigarette lighter outlet on it to power another inverter which also allows me to monitor the batterys level so I don't have to wonder as well as pulling heavy currents from the pack and not the Prius. No irreversible mods to the car to destroy the resale value! Camping comfortably out of my Prius by choice! Minimalist all the way! Don't overthink everything...

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I choose not to have a house hold refrigerator, microwave, or house hold coffee maker because of the amp draw & I am 6'6" and enjoy using the entire rear of the vehicle for my memory foam mattress... I have a 12 volt travel coffee maker which is much less demanding and does just fine for coffee or making hot water for oats or clean up etc... A Dometic cooler. I use usb led lights instead of Christmas lights to lessen the load too! I can fill up the Prius and disappear for days at a time just loving life! Best wishes everyone. I just beat lung cancer and today I woke up in my Prius next to the royal gorge in Beautiful Colorado! Time for coffee and a nice hike! -Cheers!

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The Dometic is way less demanding.

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I recently had someone ask how to wire up a battery charger. He bought a 25A DC-DC converter specifically for new cars with 'intelligent charging' (e.g. 15.4V chargingvoltage in new Mercedes') that the owner wants to add a second aux-battery to.

His version could limit the charging current (probably what is mentioned as being programmable through USB). And supposedly you can wire it up to the CAN bus or let some kind of internal vibration detector decide that the car is moving/running.

And those solarpanel chargers only work with a much higher voltage, I wasn't too sure if that was clear to all reading this thread.



This is the setup I had this holiday, I only had a few hours to hook it up, so I could either run the two coolers* of off the 12V in the car or of off a 24->13.8V converter running of off the 185W solarpanel (originally wired as 45V 5A but converted to 22V 10A).

I have since bought roofrails for my Prius so I can fit it on the Prius as well and will make a box that has the solar-input with 24->13.8V converter, parallel 14V input from the car with low-voltage cut off (regardless if the 12Vcar-output switches off or not when the car is not running) and possibly even a free 12V 20Ah NiMH battery**

Yes, the drag becomes awefull and you probably use a lot more fuel, but with temperatures even in Britain well above 25C pretty much every day (>75F), having the coolers run when parked up was more important to me then the extra fuel I used.


* the two coolers were about 8A current draw in total and melted yet another cigarette lighter plug. What a very, VERY poor construction they are, with a sharp pin being used to run a large current through, everyone with any knowledge of electronics knows this will heat up a lot...
** this is a 24V 10Ah electrical bicycle battery and they are worthless if the electronics say they are (e.g. if they get wet, if they detect some kind of anomaly, etc.), even if the cells are still in good working order. So they get thrown out and can sometimes even be had for free. I already used one pack to convert my 24V 5Ah NiCd bicycle battery to a 24V 10Ah NiMH battery (they are simply D-cells, so 5Ah NiCd to 10Ah NiMH conversion with the exact same measurements). It can also easily be converted to a 12V 20Ah pack. Or if I save up a few more, into a 201.6V 10Ah pack

 

What inverter do you use for your CPAP?

 

I'm glad to find out there are 12V CPAP. Mine is supplied by the VA, so needs True Sine Wave invertor

 

Hi all, I’m looking for ideas on how to solve a power outage backup using my 2007 Prius and this thread looks similar to what I want to do.

I live in a winter area where power outages can happen for 24-48 hours and need to run 60w fan on gas fireplace insert which is my main heat source. Fireplace has constant pilot so don’t need to ignite the flame. Also would like to run a small Induction hot plate to boil water or make soup. Local ski area not subject to same outages so can use WiFi and eat lunch there.

There is a thermostat for the fireplace on the outside of the utility closet, inside closet there is a cord from it running to a wall outlet.

Car is parked outside so running extension cord to inverter on 12v wouldn’t work.

I was thinking I would get 2 marine batteries and wall source trickle charger to keep them topped off then use 400 watt inverter with extension cord to the fan with a plug based dimmer switch to vary fan speed and plug in the thermostat. Then when the first marine battery runs down I recharge it in my Prius while the second one is live.

I’m not watts/voltage/amps savvy and looking at the above options is scary with multiple replies about frying expensive parts.

is there something simple like plug into cigarette lighter that will charge a 12v battery? From reading the descriptions in most products I’m seeing it looks like the cigarette based devices are to start the car or keep starter battery charged, not use cigarette lighter as trickle charger for a second battery.

Don’t necessarily care if it takes a long time or not, just that I have a way to get some juice into a drained battery and not blow up my car

thanks!

 

Lead acid batteries (like the marine battery mentioned) don't like being discharged too far. I wouldn't discharge even deep-cycle 'marine' batteries more than 50%, so I would advice some gizmo to keep an eye on that. This to prevent (too) fast degradaton of your expensive batteries.

I don't know how much current would start flowing once you put an empty battery next to the car's battery and start it up. I doubt it would blow the 100 (or 120A?) Prius fuse but I can't promise it won't blow either...
I did do a test with an empty battery hooked up to a full battery (not in a car) and that current wasn't much (>10A). This was after me suggesting these currents might be huge and people doubting this (on an electronics forum).

For new campervans with start-stop systems, there are gizmo's (special DC-DC converter) that charge the second battery with a constant maximum current because the 'intelligent' smart charging system of the start-stop system doesn't work well with a suddenly parallelled second battery. Such a device would make charging your second battery pretty safe (provided you leave the Prius in 'ready'-mode) but also slower than the maximum speed.

Finally found a link that explains this somewhat. Scroll down halfway to "So what is a Battery-To-Battery charger and how does it help?"

 

Thanks for the info, I did mean deep cycle marine not lead acid.

I have a deep cycle optima yellow top about 7 years old in my Prius currently, I’m wondering if the best bet is I just get a new one of those and use the old one as the emergency one and swap into my car and charge it as needed once the two bigger marine ones are ran down. If I have two of the bigger rv deep cycle ones and ration I think that will last a few days then a second optima Prius sized should be able to run the fan long enough to warm up my condo if an outage goes on too long.

 

By far most 12V batteries are lead acid although especially for RV's you see LFP (Lithium Iron Phosphate) more and more.

Starter batteries will have thin lead plates, which gives a larger surface for chemical reactions (that produce the electrons needed for a large starting current).
Deep cycle batteries will have far thicker plates (not prone to warping as much), so they can produce less peak current, but can be discharged further due to the thickness of the plates.
AGM and GEL batteries are still lead-acid batteries with some extra tricks (Absorbed Glass Matt will have glassfiber (iirc) matts to stiffen the inside of the battery instead of just water with sulphuric acid from 'normal' old fashioned batteries, so they can provide larger peak currents than normal deep-cycles but still be discharged further than starter batteries, the GEL is something similar with the sulphuric acid being suspended in a gel.)

The Prius has an AGM 12V battery: it doesn't have to start the car, just the computers

But they are ALL lead acid batteries and they will ALL degrade with any discharge. Starter-batteries might degrade to 80% from just one full discharge and be too far gone to start the car after leaving the dome light on, on 5 different occasions... Deep cycle might only loose 3 or 5% from a single full discharge, but if you keep it above 50%, it might only loose 0.5% of capacity*.
There is a big difference between the types, so your marine-deep-cycle is a good choice, but having a limit on how far you discharge it, will greatly increase its life expectancy.

Modern Lithium batteries are pretty much the same: if you use them 100% to 0% every day, they might only last 500 times (many phones will have some issues after about 2 years). Use them between 80% en 30% (so only half the capacity) and they will probably last in excess of 5000 times (so you can draw (half as much energy times 10 times more discharges =) 5 times more energy from it before it fails). This is why e.g. Tesla's (or any decent electric car) have the possibility to program it to charge to less than 100%. For my garage (without grid connection but with a solar panel), I charge my lead acid marine deep cycle batteries (260Ah total) with only 13.8V. They charge slower but live longer. The discarded normal lead acid starters (2x100A) are charged with a multi stage solar charger as they were free anyway.




* All numbers are just estimates based on what I think I know about batteries. Feel free to disagree, but do it after reading up on the subject enough to form an educated opinion. Or, if you have the finances, just resign to the fact they might need replacement once in a while.

 

Hi R-P , thanks for all the good info, appreciate the time you spent replying.

I just ordered a cobra 1000w inverter and am looking at options for a 1-2 amp battery tender , and a marine battery.

from reading through a lot of threads I think I’m confident enough to use alligator clips to connect the inverter to the 12v in the back , then I can use induction hot plate in my car , medium setting is about 600w.

The key thing is the 60w adjustable speed fireplace fan , which I think the fan will get 4-5 hours of use from the marine battery which should be good for 48-72 hours. Just bought the condo so will get a kill a watt and do a test run.

Then worst case if it goes longer I can stalk the closest parking spot and run an extension cord in. If I want to get fancy I could run a cord in the crawl space and out the crawl space vent or drill a hole and hope the hoa doesn’t see it

I will definitely be aware and monitor charge levels !

 

If you are going to draw 50A for a long time, I would advice to look into a better connection than alligator clamps. Or at least use clamps that have BOTH sides of the clamp wired up to the conducting wire going into the inverter. Some cheap plastic ones from startercables will have only one side connecter and are electrically only connected to the other side by means of the spring.

Also, fuse ANY wire that can pass a current appropriately. ANY 'plus' wire leaving the battery (whether in the car or in your house) should have a fuse that blows before a short can ever cause a fire. It is a fuse to protect the wire (and your car/house), regardless of equipment that is hooked up and should be sized according to wire gauge.

I've used a Speakon connector for a 600W waterheater while on car-holiday with the GF (now wife). It is on the limit for what such a connector can handle (30A per contact, there are two 'plus' contacts and two 'minus' contacts, so 60A max, here's a link to a newer one claiming 50A per contact.).

The connector is not intended for such use, but I found it safer than just clamping it onto the battery.

My 55A alternator died shortly after the trip...

 

Is your Cobra 1000W a Pure Sine Wave inverter? Modified Sine Wave may not the best choice for 600W instant demand, which is what an induction plate will require.

 

The three-quart Instant Pot models are nameplated at 700 watts, and boy are they versatile.

 

Ugh, it’s not , I thought I was paying more for a “good” one. Thanks for pointing that out.

Good to know on a fuse between battery and inverter, will add that to design.

I was a frequent poster 2007-2009 (under an account attached to a dead email address), and thought to come back and ask about this, super appreciative the community is still helpful !

 

I was considering an induction plate in my small RV, instead of using Propane. Maybe LP gas is more efficient, but I don't have as much experience with it.