I’ve a battery tender on my plow truck. Works great. It’s a small unit, about the size of a pack of cigs. I keep it under the hood and run the cord through the grill.
What I have been doing when I use the truck, is completely removing it. I would, instead, like to fix it in place under the hood (zip ties or whatever) leave it connected to the battery, and just unplug it from the 110v.
I wonder if leaving it hooked to the battery while the engine is running will damage it. I doubt it, don’t see why it would I guess. Electronics are not my gig though. I guess I’m thinking diode. The tender should have that I suppose, but don’t know if it matters.
It would be easier to just fix the thing in place and not have to open the hood in the middle of a blizzard and remove the unit. Just unplug it.
In my experience, you can leave the tender connected if you are very very careful to not feed 110V power to the tender when the engine is on. You can’t have both the alternator and the tender charging the battery at the same time. That will damage the tender and maybe other things too.
The alligator clips and the wiring of the tender are not designed for standing up to the high temps / vibrations in the engine compartment. So you may want to use screws to secure them to the terminals and may want to route the wires safely.
Thanks. I need to make sure the tender and cables/wires are very secure (something I was going to do today). Since it’s a plow truck it gets a bit of a work out and things can get bouncy and rough.
I will make sure that I unplug the tender before starting. I always have.
The plow is run off the battery. Almost all are now (battery runs a motor that runs the hydraulics). I also have a winch on the back. The battery gets a hell of a work out.
I’ve toyed with the idea of getting a heavy duty/high output alternator and duel battery set up. But don’t think there is room for a duel battery.
I would advise against this practice. The cost of a small (I’m guessing it’s between 2 to 5 amps) charger is minimal. The cost of possible damage to the battery charging circuit or overheating charger cables could be significant. While the charging voltage to the battery (and to the battery charger output) should be within a reasonable voltage range, the capacity of the car charging system to provide significantly more current than the charger is intended to handle is very high. In essence, you would be relying entirely on the design and the components internal to the charger to protect against back-voltage.
If you want to attach the charger permanently, I’d strongly suggest using the quick disconnect that many of them have (or which you can install yourself) to disconnect the unit from the battery when not in use. As an alternative, you can install a separate heavy-duty diode unit to protect against back-voltage. (These are available from car and RV parts stores.)
TL;DR: I wouldn’t trust the charger to protect itself against back-voltage.
I hear ya ZonexandScout. The drag from me is winter. It can be very difficult to open the hood even. Yes I push the snow off, and yes I’m a big guy. But ass deep in snow is ass deep in snow.
I could rig a disconnect from the tender and mount it on the grill I suppose.
My plan is to unplug the tender from the 110v, start the engine (leaving the tender hooked to the battery), and check for heated cables etc. If all looks good I’ll make a more permanent mount for the tender under the hood.
I’ve thought about a solar trickle charger. I had one for previous plow truck. Didn’t work. There is so much snow, there is no where to put it on/in the plow truck to get sun. Average annual snowfall is 25.5 feet.
It’s easy enough to test.
Just put an ammeter in series with the battery tender leads, unplug it, and turn the engine on. If the current reads zero, you can leave it connected all the time. If the current is non-zero, but very small, you are probably safe.If the current is large (like anything over 250mA), I would not leave it connected.
I just get nervous about the idea of the relatively high-current-capable charging circuit from the vehicle being connected directly to the itty-bitty circuit board in the charger. I’ve got to assume that the designer of the charger did their best to make the device compact, reliable, and cost-effective. I’m sure there’s internal protection if the battery draws too much current, but who knows how that’s designed? If a diode or cap fails, you might have a short across the charger leads. The internal protection in the charger may disconnect power to the charger, but not disconnect the output conductors. I’ve seen car audio installations where a power wire from a battery terminal to an amp has overheated from a short or excess current draw. The wires got so hot that they melted slots in the plastic parts in the engine compartment.
I used to have a Chevy Blazer and I kept a battery tender on it because of the weak battery. Because the cigarette lighter stayed connected even when the ignition was off, I kept the tender in the cab and plugged it into the lighter socket when I put the car up for the night.
Maybe instead of the heavy-duty diode, just add an in-line 5A fuse to your charger leads?
Think of it this way:
What is capable of delivering more current into a short circuit?
a) A 90A alternator.
b) A battery with 700 cold-cranking amps.
If the tender is capable of being hooked to the battery, it’s in no danger from the alternator. The only issue is parasitic current drain (and, possibly over-voltage, although that would require a really stupid circuit design).
I don’t care about the the battery tender being destroyed. I am concerned that It may overheat from the battery when unplugged from the 110v and possibly cause a fire when the engine is running.
My plan is to unplug the tender. Start the truck and make sure nothing seems to get hot or even warm. Then re plug the tender in with the truck off, and see if it’s working.
@beowolfe Not sure if I have an ammeter anymore. I threw one out for sure, don’t know if I replaced it. I have a Fluke but is made for much more ‘is it hot’ tests.
Of course, I’m thinking about the situation when the engine is running. Components can fail, especially in a hot engine compartment with a lot of vibration. If a diode, capacitor, or other internal electronic component fails inside the charger when it’s simply charging the battery, no big deal. But if it creates a short-circuit on the charging leads when they’re connected to the battery with higher charging voltage on the leads and a capability of 20+ amps, it might be bad. Depending on the vehicle, it might even damage the vehicle’s charging circuit.
I’m a worry wart. I would just feel uncomfortable with a small electronic module of unknown design and reliability being connected across my battery terminals when the vehicle is in operation. I would AT LEAST limit the current to 5 amps or less with a fuse.
You and me both (my pediatrician called me that). It’s why I started this thread. Thinking a little bit, gonna check out the truck and test a few things.
Right away on Monday morning I see a thread about something I never even heard of! This is why I love this place!
At any rate, the answer is yes, it is okay because of this reason: “The battery maintainer sends a trickle charge to your battery and can sense when it’s fully charged. At this point, it shuts off to avoid overcharging the battery, making it perfect to use when your batteries will be sitting for awhile without any use.” So, even if the battery is in use, it will sit by safely idle until it is actually needed.
Google and I pretty much know everything, so just let us know if you have any other questions.
I appreciate the info, Jasmine, but the question is NOT “can you leave a battery tender connected to a battery all the time when it is not in use?” In the OP’s case, the battery tender/charger is going to be connected to the battery terminals while the battery is being charged by an alternate source (the car’s charging system}. Many vehicle charging systems will reach over 15 VDC in charging voltage and are capable of providing 20+ amps of current.
In low voltage systems that use rechargeable 12 volt batteries, we would never use two charging sources on a single battery simultaneously. And it’s considered bad practice/risky to use one charger while the other one is still connected. And these situations are usually in a controlled, stable environment, not in a hot engine compartment vibrating down the road at 65 MPH.
Caveat: It may work just fine and never have a problem. But people often turn off the water supply to the hoses to their washing machines when they leave a house unoccupied…simply because the results when everything ISN’T OK are pretty bad.
