Toward the end of determining how many "external" car batteries can I put in parallel with the car battery, without over-loading the alternator??
I know the charging current draw would depend on the degree of discharge of the batts, so figger 50% discharge. Or even total discharge, ie, a dead battery.
I figger that if no lights, defrosters, etc are being used, the alternator could handle two extra batteries, charge-wise.
Have I figgered right?
Is there such a thing as a "current limiter", so that the alternator would never "short out", from too many loads?
Depends on what alternator you have and how fast you want to charge the batteries. Some of the small GM high output alternators cannot put out high current for a long time without failing. The large-frame old Mopar units could put out full rated power (I believe theat was as high as
114 amps) day in and day out. The big Lecce Nevilles used in ambulances and busses were good for full output steadily as well. Many of the lightweight high amperage units in current use can handle charging one dead battery with no problem - 2 big ones might be hard on them.
I know guys who have a switch/relay to disconnect the "coach battery" and only connect it when the main battery is up to charge to prevent overloading the alternator. There are kits to beef up the little GM alternators with a better rear case for better cooling and a stronger bearing.
That's what I plan on doing. The main car batt will never be discharged, so really the only extra load will be the one or two "carriage" batts in the back. If I have to charge them one at a time, so be it. Hopefully I won't learn anything the hard way.
Speaking of learning the hard way, if I do try to charge two farily discharged batts at once, what might be an indication that it is tough on the alternator? A low charging voltage? What would approx acceptable limits be?
fwiw, the two vehicles at hand would be an 04 Nissan Frontier, 07 Honder Shit, I mean, Fit -- ackshooly a good car, so far. I'd sure hate to have to change out alternators, tho....
Your car alternator is probably capable of generating about 40 amps, which basically means that it will re-charge a fully dead 40 amp-hour battery in about one hour.
An average car battery holds ~ 40 ~50 amp-hours, do the math.
AFAIK the alt regulator does that just fine by design, so just stay within what it was designed for, Find the particular alt specs. If you're still thinking about using the car and an inverter for home power during outages, think small watts, or get a generator. Cars alts aren't meant for continuous high watts at 120v. But 500-600 continuous 120v watts from an inverter is easy for a typical car alt, and so is a peak 1200w for starting a fridge. You won't hurt your alt or battery. So figure out what you want to power during an outage. I'd say if you want more than 600w continuous, get a generator. The multiple battery issue isn't normally applied to cars. Check out boat and solar power forums. I know they use isolator switches to handle loads, but that's just from reading. I don't even think about adding batteries to a car. Maybe if I had a truck... Back to 120v inverters running from a car, the main issue is the cables. You need something like what's found here.
formatting link
Look at the #1/0 AWG CABLES. That site has a lot of info about inverters. The cabling is what stopped me. Just didn't want to deal with the connection issue. Have to remove an engine brace to get at the battery. There's an easily accessed covered lug for the +, but I'd have remove the brace to get at the -, or set up a stud to ground on the engine. Too lazy to do that for something I might never need. If I ever decide to spend the 4 bills or so for a good set-up I'd do it. You also need to fuse the cable. Another thing is cable length. You really need to shelter the inverter from rain/snow. I figured 6' cables would get under the garage door to the inverter. Could run the car in the garage with doors open, but I don't like that. So inverter location has to be considered. Anyway. that's about where I stopped thinking about setting up an inverter. Not many power outages here. I do like the idea for emergency use.
Basically your alternator charges at its maximum current into a discharged battery. If you connect two discharged batteries it doesn't "short out" it just keeps right on producing its maximum current. You need to look up what your alternator can put out on a continuous basis with whatever cooling it has without overheating. If you have, for example, a 60 amp alternator then the alternator will put out its maximum 60 amps without damage.... assuming of course that it doesn't overheat.
Your best bet would be to have a look at some of the yachting or RV installations where a guy has, say a 6 - 700 AH battery bank and a single alternator to charge it. Or perhaps have a look at Trojan Battery's site, they have a lot of information about deep-cycle battery handling.
I have one of the original scangauges. That was the basis for my disconnecting the alternator Q, so I could see what the diff would be. I mentioned somewhere that when the alt on my ole mazda 929S went, that my mpg's seemed to jump. Ahm still tryna figger out how to disable the alternator.... :(
But, THIS Q is for sumpn diff: I'll be adding "carriage batts" for an inverter setup, and am curious about the extra loading of the alt by extra batts.. I'm hoping johnB is right -- he's saying the max output of an alternator IS current limited, iow, you *cannot* short out an alternator?? That would be nice!
Along the lines of isolator switches below, and "sparing" the alternator, I was thinking of having two banks of batts, one powering the house, and one being charged by the car alt, and switching off as nec. Is johnB correct, that the alternator limits itself to its max safe output?? Still, wearing out an alternator prematurely is no picnic either.
At any rate, it seems like an alternator for big backup power will be stressed, either by too many charging batts or too much house load. Unless I could finagle some kind of current limiter on the alt, so that the size of a battery bank wouldn't really matter.
Yup, that's how I started this, until it grew feet. Sam's Club BlackMax
8750 W (7500 continuous) tested out really well. Noisy, but you could load the shit out of it, and still have PC-stable power. I was going to do the tri-fuel conversion.
I found that site. He's serious about inverters!!
I would use a side/screw terminal batt, and mount the inverter directly to one battery, via bus-type bars, which you can make out of 1/2" copper tubing, crushing it flat. Wire gauge is now moot. If I used a second battery, I'd proly bus-bar that as well, mebbe use the main section of the copper tube un-flattened, for structural positioning of the batts in the truck bed.
Have to remove an engine brace to get at the
Well, I wouldn't really deal with the hood battery. I'd use that batt only in conjunction with the alternator, when charging the inverter batts. So cabling between the alt/car battery to the inverter batts could be much thinner, on the order of #12 housewire -- which is actually good for up to
50 amps (not code-wise, of course).
And this strat holds whether your batt/inverter is on the vehicle, or off the vehicle, as long as the inverter itself is "bussed" to whatever batt bank you are using.
As per the above, you can just leave the car outside, as the only cable(s) you now have to worry about are 1. the charging cable from the car alt/batt to the inverter setup, and 2. the AC wire from the inverter output to the house. Both are now pretty thin-ish.
I'm forced to do a lot of hanging out in my car/truck, in the cold no less, so there are many advantages to this system, many applications. Just one of them being, you'll never need a jump with extra batts!
Proly the *least* practical to all this is the power outage scenario (as I am realizing), but a cupla cars providing 600 W or so each is a whole lot better than nothing. Not many people appreciate the whole risk/reward, cost/benefit of this, re the probabilities.
But holy shit, people are going to be without power around here for weeks, and this is the THIRD time in just a cupla years. Funny, prior to all this, my power was truly erratic, but I lucked out during Irene, the Halloween snowstorm, and Sandy. But my luck can't hold out forever. But the probabilities are why I hesitate to go the whole generator route (again), bec that's no picnic either. But once it actually is set up, it's pretty seamless. Lotta work, tho.
Most of my neighborhood is without power. I'll see how long it takes them to get back up, and that will affect my prioritization for another genset. If it's more than a week, I'll be getting another genset by next summer, screw the probabilities.... :)
I've lost the logic of this. If your objective is to have emergency power at home, why do you want to haul around hundreds of pounds of batteries that don't need charging?
Put the batteries adjacent to the inverter. You want the long cables from the alternator to the battery at 40 amps instead of between the battery and inverter at hundreds of amps. Put a smart trickle charger on the batteries. Hook up the car in an emergency to charge 'em when the grid is down. I haven't done measurements in decades. It would be interesting to know the car engine RPM required to get 40A out of an alternator.
The primary result of putting the batteries in the vehicle is to reduce gas mileage and wear out your brakes faster.
Or you could buy a $89 Harbor Freight generator that will give you more reliable power for longer and cost less than the inverter and be portable.
If one insists on having 12 volt batteries, one can wire the batteries into a "charging station" which charges them off main power, till the power goes out. Add a genset of some sort to recharge them when the main power is out. I understand that Coors (of all people) is doing some interesting work in ceramic batteries, with such an idea in mind.
-- pyotr Go not to the Net for answers, for it will tell you Yes and no. And you are a bloody fool, only an ignorant cretin would even ask the question, forty two, 47, the second door, and how many blonde lawyers does it take to change a lightbulb.
Yeah, I haven't gone through that, just imagined it. My favorite idea is to get out of town for the duration, but that's not practical for many people. Only conclusion I've come to is if I bought a generator it would run off natural gas, and if I somehow ended up with a gasoline generator I'd work out a siphon system from my car gas tank. Most I went without power was 3 days. What did I miss most? TV and PC. A battery radio filled in, but I wished I had a TV and my PC. Damn, it was boring, waiting for the power to come back. A real good time for a fishing trip.
During a power outage I want TV and especially Internet weather radar for the current weather forecast, to know whether to open up and repair or temporarily cover damage.
Recently I bought about the oldest widescreen dual-core laptop that can run Windows 7 + Media Center and added a USB TV tuner so it gives me both HDTV from an antenna and Internet from a cell phone modem, or the landline if it's still up. It consumes 30 - 40W which a truck battery and inverter will provide for a long time.
Of course, since I was prepared, Sandy didn't knock out power on this street. Usually here an ice storm means a week's outage.
Until it catches fire and burns your house down. Every harbor freight tool I have ever seen has wound up failing in some way that got people injured, from the anvil that split apart leaving half of it to fall on my foot, to the spot welder that ignited in my friend's hands.
That's a good idea, a laptop that pulls in TV. I've resisted laptops, but you might have changed my mind. It could pull some double-duty for vacations too.
That's always the big question. Do I really need it?
First, make sure you use a Deep Cycle battery or batteries for your inverter bank in the trunk. And it's best if you make a sealed battery box that is vented to the outside of the trunk top and bottom
- Batteries have Sulfuric Acid inside them and release Hydrogen Gas when they charge, best to get that outside the car. The little Scoop Vents and 3" hose from a boating supply will work well for that.
It is NOT recommended, but if you use two 12V Batteries in Parallel, they must be a matched pair in brand, model, and manufacturing date. Otherwise one battery with the better connections and/or lower internal resistance takes all the load and does all the work - then it shorts out and kills everything. This is bad.
If you need more than 105 AH capacity, it is far better to get two 6V Deep Cycle Golf Cart batteries (some Costco's stock them) and you wire them in Series - (-) of #1 to chassis ground, (+) of #1 to (-) of #2, (+) of #2 to Alternator and Loads. That will give you around 200 amp-hours with GC2 batteries.
DO NOT try running a large inverter off the starting battery - unless you have a huge alternator that can supply most of the load and you have the engine running at above 2,000 RPM to get full output, or you WILL wreck the starting battery by running it down deep.
Second, the regular car battery WILL need recharging after you start the engine - that was a 250A load you just put on it for 3 to 5 seconds running the starter motor. And since the alternator doesn't put out full current below about 2000 RPM the battery is supporting the loads whenever you are sitting at a stoplight at night.
The alternator will not "Short Out" - it tries to put out 13.8V up till it runs out of current and then the voltage drops to what it can produce - until it starts to overheat and it cuts itself back. Once the batteries get charged the current will drop off, and the voltage will come up to the 13.8V "float charge" level.
Stuff in as much alternator as you can under the hood, so it isn't hitting that thermal limiter much - lots of cars have optional heavy-duty alternators available that drop right in and give you a 20A to 50A bump in output. And you need a heavier cable from the alternator to the isolator.
If you want more than 120A to 140A output there are new aftermarket alternators available from several makers, but they aren't cheap. Go to a smart person running an Auto Electric Shop - they'll know where to get you rebuilt truck alternators far cheaper, and they'll last just as long. Sometimes they can put the Truck alternator innards in a Car alternator case that fits your car.
Or they put in a Leece-Neville where the rectifier diode stack and regulator are in a separate external box - this is needed on Vans used as ambulances, where there just isn't any space under that Doghouse for a physically bigger alternator. They stick the rectifier under the passenger seat.
Install a Diode Battery Charge Isolator - and be sure to wire the fourth stud voltage sense lead back to the alternator (follow the instructions) so the alternator voltage regulator sees the 0.5V drop through the diodes and adjusts itself up to compensate accordingly.
Most alternators have the external sense lead - If the car maker leaves that terminal disconnected (normal cars) it uses the Output wire as the reference source. But if the regulator sees voltage on that sense line, it switches to that as the voltage reference.
OK, so spend more money and get something better. Your choice. HF seems to be a good source for stuff you'll use rarely or never. Treat it like the cheap crap that it is and it will last longer... emphasis on the cheap.
Use the Nissan for charging. It has a 100 amp unit compared to the Fit's
Those numbers are NOT idle numbers, they are at 2,500 rpm. They drop down a LOT at idle.
If you plan on 50% discharge you don't want auto batteries, you will have to use deep cycle marine units. Auto batteries won't handle deep discharges very long before they fail.
Best solution would be to put the batteries in a box in the garage or a shed (NOT IN THE HOUSE UNLESS YOU BUILD AN EXTERIOR VENTED ENCLOSURE!) Mount the inverter nearby and use copper buss bars to feed the inverter. Then use common jumper cables from the car to the batteries to charge them. Also hook up a good battery maintainer and a solar panel and you would have reliable long term power. You could add batteries as needed, OR replace them with much larger industrial units like fork truck batteries.
As to how many batteries an alternator will handle, it all depends on how discharged they are. The curve on a typical alternator is pretty steep. They are designed to charge a low battery FAST, then as the battery comes up to charge it takes less power so the alternator works less. This isn't a problem most of the time because a battery in good shape doesn't drop very far unless you leave the lights on or crank the starter a lot.
Some interesting info on batteries and power here:
Chance favors the prepared. God does, too. I charged all my batteries, gassed up the generator. Got the generator to run (not easy). And no power out. I like it, that way.
Christopher A. Young Learn more about Jesus
formatting link
.
During a power outage I want TV and especially Internet weather radar for the current weather forecast, to know whether to open up and repair or temporarily cover damage.
Recently I bought about the oldest widescreen dual-core laptop that can run Windows 7 + Media Center and added a USB TV tuner so it gives me both HDTV from an antenna and Internet from a cell phone modem, or the landline if it's still up. It consumes 30 - 40W which a truck battery and inverter will provide for a long time.
Of course, since I was prepared, Sandy didn't knock out power on this street. Usually here an ice storm means a week's outage.
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.