Cheap electrical set-up

[Toes]

Hi everyone,

I'm being forced into my minivan due to finances. Although I'm actually kind of looking forward to it.

Anyway, my main concern right now is having some kind of electrical system to power my macbook pro, and run a fan.

I'm thinking that getting a battery and wiring up 12v outlets to it would be the cheapest way to go, but I'd like more information and idea if you have any to share.

Also, I know I can recharge said battery off the starter battery, but I don't want to potentially drain it and be stranded somewhere.
So any advice about preventing that would be appreciated too.

Thanks, everyone!

 

[Donedirtcheap]

Cheapest way is to run a fused lead from the big alternator terminal to a fuse then to a switch and then to a deep cycle 12 volt from some place like wallly world or sams. Attach a lighter socket to the deep cycle. Also get a digital volt meter and dont discharge below 12 volts. While driving turn on the switch to charge the deep cycle and shut it off when you shut the engine off. You risk draining your van battery if you forget to turn the switch off but that's about as cheap as you can do it. You could use a cheap digital multi meter found at radio shack or walmart and have it for other uses also.
You will get better battery life if you keep it above 12 volts.
Running the vehicle a short distance each day may not give you enough charge.
Thats enough for now but there is more to it

 

[Spaceman Spiff]

Hi Toes,
You haven't given us enough information to give you good advice.

First thing you need to do is determine how much electrical power you are going to use:
• How many hours a day are you going to use your computer? How many amps does the charger draw? Do you have a 12V power adapter or will you need 120V to charge it?
• Lights? For how many hours?
• How many amps does your fan use? For how many hours do you use it?
• Do you need to charge a cell phone?
• What else are you going to use battery power for?

Once you determine what your daily needs are, then we can help you develope a system that will meet those needs. The more information you give us on what your daily needs and your situation is, the better job we can do in helping. There are a lot of knoledgeable people here. -- Spiff

 

[Toes]

Spiff,
Sorry for the lack of info. Let me try and clarify a bit...
I'll probably be using the computer about 6 hours per day. It probably won't be plugged in that whole time, but for the sake of calculating power draw, let's just say it is plugged in for 6 hours per day.

The van will probably run about 4 hours per day, although it can also be battery operated, so I don't anticipate it actually using 4 hours worth of power each day.

My cellphone is just a dumbphone and is easily topped when plugged into the built in 12 volt power, even on a short drive. So I'm not really worried about that.

My iPod is always charged off my computer, so I'm not worrying about that either.

Where do I find the info on how much power each item draws?

 

[WheelEstate USA]

Driving 4 hours will not top off your batteries. Even a longer drive will only net around 80% charge. You'll need a way to give them a full charge a time or 2 a week to keep them in good shape.

Stern Wake has done some good posts on battery health. You might search some of his posts that will answer most all your questions.

 

[SternWake]

A fully charged laptop plugged in, on standby can consume as little as 0.2 amp hours in 6 hours
A depleted laptop plugged in, turned on and streaming movies can also consume 50 amp hours.

A huge range of consumption depending on the task the laptop is performing

Look on the provided power brick for the output voltage and amperage. Multiply the 2 and this is the maximum wattage it can pull.

Your words might imply you have a Hybrid minivan? I don't know how the charging systems in those work, but pure alternator recharging on a daily cycled battery will equate to short battery life.

The thicker the charging cables to the secondary battery, the faster it will recharge up to ~80%, that last 20% takes hours.

You might be able to get an OK lifespan from the battery if you can return it to 85% daily, but really a lead acid battery needs a true 100% recharge every so many cycles, and the alternator is simply a poor tool for accomplishing this.

Find a battery with a good warranty as you will likely need it.

Also put your laptop make and model# into Amazon electronics and add "car adapter" The product you buy should look like the provided power brick, but have a ciggy plug on it. This will use considerably less battery power than if you were to buy an inverter and use that to power the provided power brick.

Avoid 'Universal' car adapters, especially if your provided power brick is more than 60 watts.

 

[Spaceman Spiff]

Hey,
No need to apologize. You sound like someone who just plugged stuff into the wall, not thinking about how much power you were using. I was there a few months ago.

I'll probably be using the computer about 6 hours per day. It probably won't be plugged in that whole time, but for the sake of calculating power draw, let's just say it is plugged in for 6 hours per day.

I looked up the MacBook Pro and it's power supply uses 4.6 amps at 18.5 volts (there should be a tag on your power supply with this information). At 6 hours: 4.6 amps x 6 hours = 27.6 amp-hours taken out of your car or house battery. If you don't have a power supply that plugs into your cigarette lighter, you will need an inverter (to convert the battery 12 volts to 110 volts of your 2 or 3 prong plug) which takes 4 amp-hours => 27.6 + 4 = 31.6 amp-hours.
Using a fantastic fan on medium for example: 1.4 amps x 6 hours = 8.4 amp-hours. Now we are up to 40 amp-hours per day.

The van will probably run about 4 hours per day, although it can also be battery operated, so I don't anticipate it actually using 4 hours worth of power each day.

I guess I don't understand what you mean by battery operated. Somehow, you are going to have to replenish the ~40 amp-hours taken from your battery every day. 4 to 6 hours a day of driving may or may not get the battery back to 80% capacity (depends on a lot of variables).

Where do I find the info on how much power each item draws?

All electrical appliances have a tag listing their power consumption. Your MacBook power supply tag should say 4.6 amps or 85 watts at 18.5 Volts (watts = volts x amps).

Bindi (smart dog) gave you good advice. Start searching the site. A lot of others have gone down the same road. -- Spiff

P.S. Just saw SternWake's reply. Might want to read some of his recent posts. Also, some of the recient builds talk about setting up their electrical.

 

[Toes]

Hey everyone, sorry, that was a typo. I meant to say the FAN will be on about 4 hours a day. And it can run on batteries.

 

[Donedirtcheap]

http://www.cheaprvliving.com/blog/baby-steps-electricity-car-van-little-money/

 

[Toes]

Genius! Thanks, DirtCheap! Somehow I missed that article.

I should add that I am pretty handy with tools and know how to do basic electrical work as long as it's not too complicated. I like the simplicity of this setup. The only thing is I tend to be pretty forgetful and I don't want my car battery to drain if I forget to unclamp the cables, or flip a switch.

Is there a way to keep cables between the two batteries connected and have the car battery charge the house battery only when the car is running, without having to deal with switches or clamping and unclamping things?

Thanks for the help so far, everyone!

 

[Donedirtcheap]

Genius! Thanks, DirtCheap! Somehow I missed that article.

I should add that I am pretty handy with tools and know how to do basic electrical work as long as it's not too complicated. I like the simplicity of this setup. The only thing is I tend to be pretty forgetful and I don't want my car battery to drain if I forget to unclamp the cables, or flip a switch.

Is there a way to keep cables between the two batteries connected and have the car battery charge the house battery only when the car is running, without having to deal with switches or clamping and unclamping things?

Thanks for the help so far, everyone!

Yes there is. Search and read sternwakes stuff. You can use a continuous duty solenoid that will turn on when the van is running. I think he mentioned using the heater circuit to energize the solenoid but read up as I'm not sure. Remember its a continuous duty solenoid not a reglur ole one.

 

[Toes]

Remember its a continuous duty solenoid not a reglur ole one.

What's the difference between the two?

 

[Donedirtcheap]

A continuous duty solenoid can be energized for however long you like. A intermittent duty solenoid that is commonly using for starting engines is designed to be used for a short time. A continuous duty solenoid will generally use about .70 amp to keep it energized. An intermittent duty will draw about 2.7 amps. So....if you were to wire it without a solenoid and you can remember to always shut the switch off when you shut your engine off you will have more energy available for charging.

 

[Toes]

Ah I see. Thanks!

SternWake mentioned a "dumb CD solenoid" in a couple posts. Would this fall under the continuous duty of the intermittent duty?

 

[wayne49]

Toes:

CD == Continuous Duty

I like the electrical diagram.

-Wayne

---

PS
dumb == not smart

 

[Donedirtcheap]

Probably, with the smart ones being latching or a type made by Blue seas that he has mentioned which I believe were basically automatic current sensing. Too expensive. Stay with the basics while you get used to things.

 

[Optimistic Paranoid]

As an example of a non-dumb solenoid, I'm familiar with one that combines a solenoid with some computer chips. When the engine starts, the chips sense the rise in voltage caused by the alternator, and they activate a timer circuit. For the first five minutes, ALL of the alternator output goes to the engine battery, to make sure it comes back to full charge. After the five minutes, the chips energize the solenoid so current can flow to the house batteries.

Regards
John

 

[SternWake]

A dumb solenoid needs 12 volts from another source to activate the electromagnet and connect the alternator to house battery, or starter battery to house battery.

A smart solenoid either senses charging voltages and combines the batteries, or uses a timer delay when it senses charging voltages.

A latching solenoid only needs a momentary burst of 12v to activate the solenoid and the latch holds the contacts together.

It also needs another momentary 12v burst to unlatch the solenoid. Hard to make a latching solenoid completely automatic.

Feeding a latching solenoid 12v continuously will overheat it in a short time and likely fust the internal contacts, rendering the solenoid useless.

A Solenoid is basically a large Relay. The Blue seas Automatic Charge Relay is a smart latching solenoid.

please see post 44 in this thread
https://vanlivingforum.com/Thread-Starting-the-solar-set-up?page=5

 

[Toes]

Ok, so as far as starting off with a cheap setup, I've decided to go with one 12v battery.

I'll likely kill it prematurely while I get the hang of all this, but it's better to do that then kill a pair of Rolls Surrettes due to lack of knowledge.

So I'm figuring a good "marine" battery is what I need?
Any recommendations?
Also, how do I know if it's a marine battery or a regular starting battery? Will it say somewhere on it?
And finally, what's with all these group sizes? I understand they show the actual physical size of the battery, but they don't seem to be consistent across battery types. Is it better to go with the biggest size you can?

 

[Optimistic Paranoid]

Marine batteries have dual connection posts. The regular top post like you find on car batteries, plus a couple of threaded studs to be used with wing nuts.

Check the weights of batteries you are interested in. Lead is heavy. The more lead in a battery, the more deep cycle it is.

Battery group sizes are something the battery industry came up with a long time ago and still use. (Sort of like the way modern shotshells are still marked with "dram equivalent weights" of black powder) There is no apparent rhyme or reason to the numbers.

Basically, try to buy the most amp-hours you can get, keeping in mind that you will only be able to use half of them.

Regards
John