# 90 ah 12 volt deep cycle battery > inverter > electric blaket.. feasible?

#### Deanosaur

Joined Dec 3, 2013
5
Hello new here! Let me start with I'm differently a layman in this area and this will be learning process for me.

I know RV's, campers, and big trucks used 12/6volt power banks for to juice electronics while off the grid. With that in mind I wanted to make a single battery power pack I can used for different things while off the grid car camping.

Material wise I think I know what I will need but I don't know if I can power some of the devices I had in mind with a single 12volt / inverter.

My first question is just to get a estimate or idea's how long I can power a low volt electric blanket with this kinda of set up. My understanding is I would have to do some hands on testing to find out a true measure but for now I just need a ruff idea.

My vocabulary and knowledge is limited in this are and I do plan on using the resources here to educate my self but its slow learning process for me =\

tl;dr

Anyways to the point. Say I have a 90ah deep cycle battery hooked to a inverter. And from that I have a 12volt electric blanket/pad that at max uses 100watt of power.

How long can I run that blanket/pad with just that info so far? I will get into more detail about winter project soon.

And nice to meet you guy.

#### Deanosaur

Joined Dec 3, 2013
5
Was to late to edit the post but I need to fix a part.

"Anyways to the point. Say I have a 90ah deep cycle battery hooked to a inverter. And from that I have a 12volt electric blanket/pad that at max uses 100watt of power."

Its a 120volt standard plug. The blanket/pad is low volt and rates 25volts or lower.

#### tcmtech

Joined Nov 4, 2013
2,867
So you have a 12 volt battery with a 90 Amp hour rating correct?

The electric blanket will work on any voltage between 12 and 24 volts correct so could be directly connected to the battery without problems correct?

Given that info you have (12 x 90 = 1080) watt hours of electrical energy stored in your battery when it is fully charged.

In theory that would power your blanket for 10.8 hours at its full 100 watt rating.

However I have suspicions that your blanket may not need to and does not run at 100% output continuously which would mean that likely your battery could power it for a much longer time. Possibly for 15 to 25 hours or more.

#### Deanosaur

Joined Dec 3, 2013
5
So you have a 12 volt battery with a 90 Amp hour rating correct?

The electric blanket will work on any voltage between 12 and 24 volts correct so could be directly connected to the battery without problems correct?

Given that info you have (12 x 90 = 1080) watt hours of electrical energy stored in your battery when it is fully charged.

In theory that would power your blanket for 10.8 hours at its full 100 watt rating.

However I have suspicions that your blanket may not need to and does not run at 100% output continuously which would mean that likely your battery could power it for a much longer time. Possibly for 15 to 25 hours or more.
Yes its 12volt deep cycle battery with 90ah. The blanket/pad (thinking of buying don't own yet) uses a standard 120volt wall plug. It operates at 25volts or less. With around 100watts or lower if the heat settings are down.

So I will need to use a inverter for it. What kind of loss can I expect from a inverter? My understanding so far is it will have a operating power and its not 100% efficient.

If I can I want to use this power box this winter to car camp at ski resorts. Although I can handle backpack sleeping and could simply bundle up in my winter bag. I rather have more cozy set up for nice nights sleep. I have hatch back that the seats fold down and I can fit nice sleeping mats in while having room to stretch out. With placing reflective mylar pad under it for radiant insulation. I have ideas how to deal with ventilation and other problems that could occur sleeping in a car. The main part I'm thinking of is heating blanket / or mattress pad I can power all night or off and on with a switch for warmth. Ideally I just wanna use worm insulating blankets on top of it. With sock and good snow hat on the only comfort issue If foresee is a cold face. That I can deal with ^^

This is mostly to drive up the night before to get first runs in. The resort near me are 1.45hrs - 3.5hrs away. Making the drive tiring its self.. almost never get make it in at opening like I want. Though I could see my self doing more then that.

Future planes with the box would be for summer car camping or something like where it would be nice to power some led lights or boombox for while. Attaching a solar panel for few nights off the grid sounds like a nice set up to have around. I know one batter is not a lot of power but gives me something to play with.

#### BobTPH

Joined Jun 5, 2013
5,259
You would be better off bypassing the inverter and the power supply of the blanket, and connecting the 12V directly to the low voltage side of the blanket. That way you get 100% effiiciency. Going through an inverter + step down power supply would probably give you at most 70%.

Bob

#### wayneh

Joined Sep 9, 2010
17,168
The blanket/pad is low volt and rates 25volts or lower.
How do you know this? Is it 25V AC or DC?

I'm with Bob; as long as the blanket is meant for it, just bypass the losses (and fan noise?) of the inverter and connect directly to the battery. Use the inverter only for things that really need it. With anything you power, consider how you might do it directly instead of using the inverter.

On the other hand, the answer to your first post is, yes, it is feasible and simple. In fact, the heat wasted by the inverter will be dissipated into the car, so maybe it's not really so bad. Noisy though.

#### tcmtech

Joined Nov 4, 2013
2,867
On the other hand, the answer to your first post is, yes, it is feasible and simple. In fact, the heat wasted by the inverter will be dissipated into the car, so maybe it's not really so bad. Noisy though.
That would depend on the type and size of inverter he is using. The little 100 - 150 watt ones that plug into the lighter/power ports don't have fans and are very efficient.

#### Deanosaur

Joined Dec 3, 2013
5
First off thank for the reply guys.

You would be better off bypassing the inverter and the power supply of the blanket, and connecting the 12V directly to the low voltage side of the blanket. That way you get 100% effiiciency. Going through an inverter + step down power supply would probably give you at most 70%.

How do you know this? Is it 25V AC or DC?

I'm with Bob; as long as the blanket is meant for it, just bypass the losses (and fan noise?) of the inverter and connect directly to the battery. Use the inverter only for things that really need it. With anything you power, consider how you might do it directly instead of using the inverter.

The blanket technically runs off DC. It has a small power supply box that converts AC to DC. They advertise this for safety with spills and the fires old blankets were know for. Additionally they work consistently with MSW inverters. Witch new generation digital AC blankets/pads almost don't at all. There is no way to directly connect to DC source. It was designed to use to use the proprietary power box.

The brand is softheat and I will order it from amazon if I go with this idea. I got the heads up on it from a RV forum talking about off grid heating. Found a chart stating it the particular one I have in mind used 102watts on high down to.. ugh lost the chart but it was well under 50watts on its lowest setting.

#### Deanosaur

Joined Dec 3, 2013
5
That would depend on the type and size of inverter he is using. The little 100 - 150 watt ones that plug into the lighter/power ports don't have fans and are very efficient.

You would be better off bypassing the inverter and the power supply of the blanket, and connecting the 12V directly to the low voltage side of the blanket. That way you get 100% effiiciency. Going through an inverter + step down power supply would probably give you at most 70%.
I would like that best. I was thinking of powering other things. Maybe I will get a low watt fan-less inverter that's more efficient for the night time with the blanket. And keep a higher watt one for other devices or occasions.

Anyone know how I can figure estimates or what I should use as base estimate for loss threw 400-1500watt inverters? I don't understand how that works yet. Does high watts = less efficient..

On the other hand this is box I'm going to house it in for carry. It has two 12volt plugs and direct connect studs. Its for trolling moters but will work good for me I think. Was going to wire up the box my self but I ran into this on amazon. It only holds group 24/27 size so it would work if I can get way with the batter I have now.

http://www.amazon.com/MinnKota-Trolling-Motor-Power-Center/dp/B001PTHKMG

#### wayneh

Joined Sep 9, 2010
17,168
Anyone know how I can figure estimates or what I should use as base estimate for loss threw 400-1500watt inverters? I don't understand how that works yet. Does high watts = less efficient.
Without more specifications, I would just use an estimate such as 25% loss. So if you're lighting a 100W bulb, an additional 25W will be drawn from your battery and dissipated as heat into the vehicle. That's probably close enough.

I suspect that the higher-rated units, being more expensive, are a bit more efficient than the little cheap ones. Those are made with different design goals. I also suspect that all these devices are more efficient when operated well below their max rating. These are just hunches.

#### ErnieM

Joined Apr 24, 2011
8,315
One thing to keep in mind is if you use a 90 AH battery to get 90 AH you don't have to worry about recharging it: it will quickly become a disposable battery as it will fail very quickly.

Limit how much power you get out of the battery and the battery will give you a much much longer life.

#### bountyhunter

Joined Sep 7, 2009
2,512
+1 Even "deep cycle" lead acid are very limited in total energy they can deliver in a lifetime. If this project was mine, I would build up a battery using Li FE PO4 batteries which tolerate deep discharge very well. Shorai makes 12V batteries off the shelf.

I would also get some real data about the load profile: how much does it draw, what duty cycle, etc.

#### tcmtech

Joined Nov 4, 2013
2,867
+1 Even "deep cycle" lead acid are very limited in total energy they can deliver in a lifetime. If this project was mine, I would build up a battery using Li FE PO4 batteries which tolerate deep discharge very well. Shorai makes 12V batteries off the shelf.

Have you compared the cost of a common deep cycle 12 volt 90ah LA battery to that of a equivalent Li FE Po4 battery? From what I am finding online the OP could buy 10 or more standard deep cycle LA batteries or 5 AGM type for what one 12v 90 Ah Li Fe Po4 would cost!

#### bountyhunter

Joined Sep 7, 2009
2,512
Have you compared the cost of a common deep cycle 12 volt 90ah LA battery to that of a equivalent Li FE Po4 battery? From what I am finding online the OP could buy 10 or more standard deep cycle LA batteries or 5 AGM type for what one 12v 90 Ah Li Fe Po4 would cost!
It's a question of cycle life. You have to use an electric blanket every night. Even a deep cycle lead acid battery is going to get killed quick deep cycling it every day.

Li Fe batteries cost more but have many hundreds of charge cycles in them.

#### tcmtech

Joined Nov 4, 2013
2,867
I would say it's up to the OP as to what he wants to do but for me spending $1000 on a single battery for weekend camping expeditions in a car is nuts and a total waste of money. If I had to do it at worst I would buy a pair of cheap 6 volt 225 ah golf cart batteries and wire them up in the trunk with a 6 gauge cable going directly to the car battery and be done with it. Even at 0f and running the blanket at 100 watts the whole night they would never reach lower than 1/4 charge. less if you figure having the car battery tied in with them. I am not sure where you guys get your battery life concerns from. I live out in the country and we have over two dozen vehicles and machines that run normal starting batteries of which most get run down numerous times a year and battery failure is still very uncommon for us. To be honest a number of our vehicles and machines tend to drain their batteries dead flat a number of times a year and they still make it a 3 - 5+ years before needing change outs. My brother has an electric golf cart that has cheap 6 volt 225 ah deep cycle batteries in it and thanks to my nieces they spend more time stone dead than properly charged up and they are several years old now. If given a full day to recharge his cart will run and drive the same distances it did when they were brand new. #### bountyhunter Joined Sep 7, 2009 2,512 I am not sure where you guys get your battery life concerns from. Personal experience. My motorcycle came from the factory with the "lights always on" system meaning it taxed the battery more when starting because of the extra drain on the battery. The first three batteries averaged less than 1.5 years life. I rewired it to disconnect all lights until the engine started and now I average 6 years of battery life. Less discharge = longer battery life. Full or Near Full Discharge As seen above, allowing a battery to stay in a state of not being fully (or nearly fully) charged will lead to sulphation problems. What's more, fully discharging (or nearly fully discharging) can cause such changes to the battery's chemistry that it will not readily recharge. http://www.solar-facts.com/batteries/battery-failure.php The life of a lead acid battery can be determined by 4 key factors: • Cycle life – This is essentially how many charge and discharge cycles the battery can tolerate. If the battery is cycled frequently, its life will be shortened. Lead acid batteries should never be run completely flat, the recommended minimum charge is approximately 25%. http://www.mynrma.com.au/motoring/car-care/lead-acid-battery.htm Last edited: #### crutschow Joined Mar 14, 2008 30,127 Why not use a 12V blanket designed for RV/car use? That will avoid the cost, inefficiency, (and possibly noise) of a 12V to 120V inverter. #### tcmtech Joined Nov 4, 2013 2,867 Less discharge = longer battery life. Ah I see. Batteryophile standards. I go by hands on experience. If a battery does what it's supposed to for as long as I needed it to that's more than good enough and there is no need to waste money going above and beyond for a just in case scenarios that likely wont happen or at least that would never justify the extra upfront costs. I don't waste my time and money concerning myself about theoretical ideal based "what if's'. As for the OP I have suspicions that if he is camping out in his car at night and needs an electric blanket to stay warm rather than burn fuel running the engine to stay warm just so he can go skiing early the odds are he does not have loads of money to be throwing away to begin with. I know when I have went scuba diving and stayed over night I just let my pickup run all night to stay warm which maybe cost me$10 in fuel at the worst. Also for the maybe five times I have done that in the last five years it would take me the rest of my life to burn $500 worth of fuel. #### crutschow Joined Mar 14, 2008 30,127 .................................. I know when I have went scuba diving and stayed over night I just let my pickup run all night to stay warm which maybe cost me$10 in fuel at the worst. Also for the maybe five times I have done that in the last five years it would take me the rest of my life to burn \$500 worth of fuel.
Trust you didn't sleep in the pickup since that's a good way to get carbon monoxide poisoning.

#### tcmtech

Joined Nov 4, 2013
2,867
Trust you didn't sleep in the pickup since that's a good way to get carbon monoxide poisoning.
Pretty hard to gas yourself with my pickup when it is sitting on a open beach free and clear in all directions.

Or at least I can come up with about 10,000 other things more worthy of worrying and losing sleep about.