Battery tender in the absence of a power outlet

Hi everyone,

I would like to hook up a battery tender but unfortunately my car is parked in a common garage without an electrical outlet nearby. Do any of you guys know of a way to power a battery tender with another battery (perhaps a spare car battery)? I have researched this question on the net extensively without any luck, I was hoping you guys might be able to provide some answers or insight into this question. thanks in advance!

 

You can get a converter that will take 12 volts and turn it into AC for a battery maintainer. Many SUVs and most motor homes have an AC outlet on the vehicle.

If the car is driven at least once a week, it should not be a problem. You could also ask the building owner to provide an outlet for you. If the garage has lights, running conduit to an external plug would be pretty simple. You might get charged for it, but that is probably better than having an extra battery in your car.

Taz
Terry Phillips

 

Yup! Best charger is the cars alternator - drive that puppy!

Alternatively a new battery should be fine two weeks apart once you then go for a decent run.

 

taz ang greg,

thanks for your replies. im going to give the car battery/power inverter method a shot and see how well it works. I'll let you guys know how it goes, thanks again.

ernie

 

I heard of one guy who had trouble with his high-rise condo manager for trying to plug into common power for his battery maintainer.

I think he looked into a photovoltaic cell ("solar cell") for a low current maintainer, as the garage florescent lights were on 24x7.

 

Have you got access to the roof of this garage? Battery tender now has a solar option. We put one on the race trailer to make sure the batteries are always maintained. Only a few months old, but so far, so good.

Rick

 

Do those use single-crystal or amorphous solar cells?

From what I've seen, the single-crystal cells (like on a solar calculator) need light in the visible to infrared range, and don't work as well in overcast conditions, but will work off incandescent lighting; while amorphous cells, like the NPower, work in the visible to UV range, so they work in overcast and can produce some power off fluorescents.

Obviously, solar panels aren't going to produce as much power off garage lighting as off sunlight, but if the garage lights are on all the time, you're not limited to sunny daylight hours.
But you'd need "solar" panels that run off wavelengths that the lighting provides.

 

Don't know... but I'll check the paperwork.

Website doesn't say either....

http://batterytender.com/solar.html

Rick

 

Excellent post, Taz

 

I have a little experience with this stuff, so I thought I'd share what I know. I have a number of cars as well as a pair of agricultural tractors that I use solar to keep a full charge on. I also run the home alarm system, networking hardware and video security from a standalone battery bank which is kept charged with solar. I laugh when the grid power goes down

With regard to batteries:

If I was storing the car for an extended period of time, I'd look at installing one of the so-called dual purpose batteries that can perform deep cycle duty as well as engine starting. These things have thicker plates than a starting battery and can tolerate more discharge cycles before failing. These are available from marine suppliers and often have a useful set of extra terminals for permanently attaching a charger.

Also AGM batteries (Absorbed Glass Mat) which keep the electrolyte suspended in a glass fiber mat have some serious advantages:

They have higher immunity to damage from discharge.

Because there is less of a gap between the plates, there is less internal resistance, this translates to higher discharge current capability, all other things being equal. It also means you get more energy density in a given case size.

Flooded batteries can leak and vent hydrogen gas during charging, almost all AGMs recombine the hydrogen and oxygen internally and thus are not vented to the atmosphere... less explosion hazard and no need (or way) to top 'em off with water.

There is not enough electrolyte in them to seriously leak if the case is damaged.

They have a much lower rate of self-discharge. Much lower.

Since the electrolyte is suspended in the mat, the electrolyte won't stratify, which can cause failures in flooded batteries over time. (Beyond the scope of this post to explain.)

You will also see these referred to as VRLA (Valve Regulated Lead Acid), this refers to the fact that if they need to vent, they can via a one-way valve... but this should not be an issue in normal care. AGM batteries are my top pick. There are more and more of these on certified aircraft as well.

Running a maintainer from an inverter:

While this works in theory, both the inverter and maintainer consume significant power on their own (relative to what's needed to charge the other battery), and the battery that's powering this setup will probably die an early death... leaving you with two discharged batteries after an extended time!

Depending on the storage time, you might be able to gain some advantage by (a) completely disconnecting the battery from the car, and (b) running a bigger battery or multiple batteries in parallel (yeah, I know that's not considered "best practice").


Solar:

It's true that the amorphous panels will generate significant voltage even in subdued lighting; that's why you see them in solar calculators and the like. The problem is that they're not going to produce significant current under such lighting, so they'll probably be disappointing if you're trying to keep an automotive battery charged with anything other than full sun for a good part of the day. They have the advantage of being cheap, and if you can put one in a sunny place, even a $50 five watt panel will keep a car battery charged without danger of overcharging. (I've seen the open circuit voltage on these at 22v on a cold winter day, but the minute you connect the load they drop right down.) The 5W panels seem to be incapable of overcharging a car battery, I've had these on the tractors for a few years, and it's great when the things start like a shot after sitting for 6 months. If you have access to sun from the garage, and can attach one of these, you won't regret it. I put a 5A inline fuse in both the pos. and neg. leads from the panel, located near where they connect to the battery. That way, if there's a fault the fuse(s) will blow before the battery tries to dump huge current into the leads.

BTW, if you go much bigger than a 5W panel you'll need a thing called a charge controller which limits the current/voltage and prevents overcharge... things are much easier with the wimpy 5W panels.

Monocrystalline, polycrystalline and other solar cells that are made on silicon substrates have exceptional service life and apparently degrade less over time than amorphous. They are also expensive: I think I was paying about $US 6/watt when I installed mine for the alarm system. I think they're overkill for charging a car battery.

Anyway, I could blather on for hours. I guess the key points are:

1. If you're replacing the battery sometime soon consider AGM. It will be more tolerant of discharge, cycling and so forth.
2. If you can do solar: The cheap amorphous panels work fine, and at $50 a go you could replace them every couple of years and not care. They'll also work fine without the need for a maintainer (which is just a fancy DC power supply anyway.)

Other than that I'm afraid you'll have to find a source of AC power for the maintainer.

If you have any questions about wiring, connectors, etc. I can tell you what I've learned.

- Charles

 

Charles,

Congats on such a clear, concise and informative post. Answered several questions I had regarding charging car batteries from solar. Thanks.

 

This isn't very practical but Rube Goldberg would be proud. Your source battery will be drained quicker by the inverter than the car's battery will loose it's charge if left alone.
A battery disconnect switch will eliminate any parasitic draw while the car rests and a good battery will sleep for a couple of months at least.
For way less than a spare battery, inverter and tender you can buy a jumper pack that'll get her started should the battery get a bit low.
Alternately remove the battery to a place with a/c power and use your tender.

Oh, if there is incandescent lighting maybe using one of those jobs that screws into a light socket converting it to an outlet is the answer

 

There is no way, under any circumstances, that artificial lighting is going to provide enough amperage to keep a battery charged using a solar panel.

 

Depends on the drain load on the battery and the size of the panel.
Amorphous works better under florescent, but produces a fraction of its rated power.
Crystaline works better under incandescent, but is still a fraction of its rated power.
A 5W panel isn't going to produce much of anything usable under artificial light. You'd need a much bigger panel.

[ame]http://www.youtube.com/watch?v=mzPPnuYsOZ4[/ame]

(Keep in mind that these tests are limiting voltage by the LED load.
While the panels are rated 5W, that would be 467 mA at 12 volt.
With the voltage capped by the LED, they'd produce maybe 2v at 467 mA or about 833 mW under sunlight.
Which is still a lot more than the 1mW (amorphous/florescent) or 6mW (crystalline/incandescent) in the tests.)

Photons are photons, regardless of source.
The energy potential is derived from photon density and Planck's constant for wavelength.

A parabolic reflector can increase photon density. But the wavelength depends on the light source.

 

hey guys: i just saw all of your replies. thank you so much for taking such an interest in my question and writing such informative and well thought out replies! I have learned a lot from this post. Im going to go with Rick's suggestion of the solar panels with the integrated battery tender because one of my parking spots is near a grate through which I can route the wires to the solar panel. will let you guys know how it works, thanks again.

ernie

 

Wow, these are very useful information for me. I usually disconnect the negative terminal of the battery & come back to start it after a month or two which has worked so far.

I'll look into the solar option or enquire about the marine battery. Thanks guys.

 

The most that the guy in the video got with a crystalline panel under a fairly strong and close incandescent light source was just over 3 milliamps. That's not going to cut it. The smallest plug-in battery maintainer that Deltran makes puts out .75 amps. That's 250 times greater than .003! That tells me that you're going to need one hell of a big panel; and keep in mind that even with your gigantic panel and a single bulb, your current output is going to tail off drastically as a function of distance from the light source. Even a parabolic reflector to gather and focus stray light can only do so much.

Sure photons are photons, but the point is that you're going to get one hell of a lot more of them from the sun than from a light bulb.

In practical terms (which I think is what we're concerned with here), I stand by my statement. Interesting video, though.

 

+1 !

Excellent post, Charles... thank you.

Mike

 

Well, thanks for the compliments! I only scratched the surface, and judging from some of the other responses I think there are a few people here who could write with similar scholarship on the subject.

Some of us should collaborate and write the definitive piece on this issue as well other aspects of automotive electrical systems as they pertain to these cars. I just need to find the leisure time to start.

Just a quick note on attaching solar panels for battery float charging:

1. I always wire an in-line fuse in series with the positive lead at close as possible to the battery. All kinds of things could cause the insulation to abrade and a short to occur. (Anything from an animal chewing the insulation to someone coming along with a pair of wire cutters.) So this seems like a good idea. Fusing both leads may seem redundant, but I can imagine some scenarios where it is advantageous, and I've done this too.

2. I initially installed diodes in series with the hot lead from the solar panel as I thought there would be some risk of reverse current flow at night. The manufacturer of the panels I bought said they are protected against this, and indeed it seems that they have an internal diode. If in doubt, something like a 100 PIV Schottky rectifier with a current rating of a few amps is fine. (Schottky diodes have a low forward voltage drop -- desirable in this situation.)

3. I think the connectors supplied with the cheap amorphous panels are pretty poor. Their only virtue seems to be that they are somewhat weatherproof. I cut them off and install Anderson Powerpole connectors right near the battery. The powerpole connectors can be crimped or soldered, will mate only one way (thus avoiding accidental reverse polarity connection), and they have a wiping action which ensures a good connection when mated. They also will un-mate easily if you forget to disconnect the panel and just start driving away, but won't otherwise fall apart. They seem to tolerate a lot of mate/un-mate cycles. (Usual disclaimer applies: just a happy customer, no affiliation with them.)

Thanks & Best Regards,
Charles

 

I would be going low tech/ghetto and plug into a long extension chord/s to some outlet outside the garage and under the door.

Fortunately, I have one outlet in the garage.

Love the solar options though. Good luck
Dave

 

What kind of car are you talking about? If it's an older one, just put in a battery cut-off switch (one of those green knobs), or in a car like the 328, just pull the battery cut-off plug out. If the battery is in good condition, it will hold a charge for months without a battery tender. And all you lose is the memory in your radio. If you have an alarm system, you can always use a separate battery for that, like a motorcycle battery. Most alarms don't draw much current, unless they go off. If it is a modern, high-tech car with a computer, you can't do the battery cut-off, but if its an old one, it's an alternative.

 

Thanks for all of the insight into this problem. I to live in a condo building with underground parking. There are no electrical outlets available and no easy way to run power to install one.
My question is: is it possible to utilize a portable power pack/jump box to plug in your battery tender. The portable power should last 4-6 days before needing re-charged.

Any thoughts?

 

power packs are not the right tool, the batteries are small and not designed for extended low current drain... check out a deep cycle type battery ( marine / RV ) which are designed to supply current at low levels for extended period of time... you can use small gauge wire to connect it to the car battery or maintainer/charger pigtail... think of the deep cycle battery as a large fuel tank

 

Cheesy thanks for the tip. Can you provide me more info like how to keep the deep cycle charged? How would I actually plug in the battery tender end attached to the car battery?
I'm trying to find the easiest most convenient way to keep my batteries charged without an electrical outlet.

 

it would be easier to get a new pigtail than match what is already there... it won't hurt to have an extra pigtail dedicated to the deep cycle battery and leave what is there alone...it will allow for choices...

keeping the deep cycle charged... it will need to be taken to an outlet somewhere ( in your apt / house / garage storage room ) ... it will depend on capacity and the amount of drain on the battery how often you will need to recharge... then what about sercurity for it, if you leave it in your space... an anchored box to conceal it would be good... depending on distance take it back to the apt... definitely with a hand truck or wagon as these weigh starting about about 50# not designed to be carried like a brief case... it will be a pain to move the battery, but less than the effort to get the car running from a flat battery...

nothing difficult, it's all simple, the hard part is physically moving a heavy battery to charge it or store it...