Is charging off of a car battery harmful for the car?

[karabiner98k]

Hello everyone,

I'm a RC helicopter enthusiast and want to fly in the field where there is no AC wall socket available for charging the helicopter's battery.

The helicopter's battery is a 7.4V 1500mAh Lipo (11.1 Wh).

My car's battery is 12.65V 74Ah.

There is a charger available for charging Lipo batteries called IMAX B6 which can use car battery as its power supply.

I just want to know that if I charge my helicopter with my car's battery (engine not running), does it damage the battery or the car?

Is it harmful?

 

[phinds]

I think as long as you don't deplete the battery so much you can't drive the car, there should be no problem.

 

[Borek]

To add to that: many LiPo chargers will stop working when the supply voltage falls below some preset limit. That's exactly to save your car battery from destruction.

I know plenty of people charging their batteries for flying this way, nobody ever complained.

 

[karabiner98k]

I'm also worried about the health of alternator. After flying when you start the car, alternator should compensate for the lack of charge. So, it should work harder to overcome the situation.

 

[Svein]

So buy a separate 12V battery and a battery charger, charge the battery at home and bring it to the field.

 

[anorlunda]

I'm also worried about the health of alternator. After flying when you start the car, alternator should compensate for the lack of charge. So, it should work harder to overcome the situation.

The extra load you cause by charging is small compared to the extra load to crank the engine when it in very cold out. That's what the alternator is designed to do. Don't worry.

 

[karabiner98k]

What is the difference between this charger and inverter?

https://www.banggood.com/nl/SkyRC-iMAX-B6-Mini-Lipo-Balance-ChargerDischarger-SK100084-p-929890.html

I know that inverter turns car battery voltage into 220V and is harmful.

What about this IMAX B6?

 

[Borek]

I know that inverter turns car battery voltage into 220V and is harmful.

Do you have any reliable source that will confirm inverters are harmful?

I have one, I use it every year in a Summer when camping in the sticks, never had any problems.

 

[karabiner98k]

Inverter is harmful because turning 12V to 220V drains a huge amount of current from the battery.
It is more than 1 or 2 seconds of cranking! or 5 seconds cold cranking.

Car battery is not a deep cycle battery and is not designed to discharge more than 20% or so.

 

[Borek]

Inverter is harmful because turning 12V to 220V drains a huge amount of current from the battery.

Depends on the power it delivers.

Car battery is not a deep cycle battery and is not designed to discharge more than 20%

During normal operation it rarely is discharged that far, but in general lead acid batteries survive discharge pretty well, as long as the voltage per cell doesn't drop below a limit.

Looks like no matter what we say, you know better car battery should be not used. If so - why do you even ask?

 

[phinds]

Inverter is harmful because turning 12V to 220V drains a huge amount of current from the battery.

I think you misunderstand transformers. It MAY drain a lot but it doesn't do so unless the load is large (for example, running a DVD player off an inverter is trivial to the car battery) and exactly the same can be said for any device hooked directly to the battery.

 

[karabiner98k]

Looks like no matter what we say, you know better car battery should be not used.

I'm talking about dry car batteries not wet ones.

If so - why do you even ask?

You didn't asnwer my question just defended your inverter against my remark!

I don't want to buy an inverter (whether harmful or not), I just mentioned it as an example for comparison.

My question was:

Is IMAX B6 Lipo charger turns 12V into 220V like inverter or not?

I think you misunderstand transformers. It MAY drain a lot but it doesn't do so unless the load is large (for example, running a DVD player off an inverter is trivial to the car battery) and exactly the same can be said for any device hooked directly to the battery.

What about charging my laptop (10.8V 4400mAh) with my car's battery? Is that a large load for my car's battery?

 

[phinds]

What about charging my laptop (10.8V 4400mAh) with my car's battery? Is that a large load for my car's battery?

No, I think even a fully depleted laptop battery would be a pretty small drain on a car battery.

 

[karabiner98k]

Does anyone here know the normal load on a car battery when the engine is running and the stereo is on?
A simple estimation would suffice.

 

[anorlunda]

Does anyone here know the normal load on a car battery when the engine is running and the stereo is on?
A simple estimation would suffice.

5 amps.

50-100 amps with a boomer speaker system.

 

[Averagesupernova]

Does anyone here know the normal load on a car battery when the engine is running and the stereo is on?
A simple estimation would suffice.

The battery should be charging not discharging.

 

[phinds]

Does anyone here know the normal load on a car battery when the engine is running and the stereo is on?
A simple estimation would suffice.

Zero. When the car is running the alternator is feeding everything, including (as averagesupernova just said) the battery.

 

[davenn]

What is the difference between this charger and inverter?

https://www.banggood.com/nl/SkyRC-iMAX-B6-Mini-Lipo-Balance-ChargerDischarger-SK100084-p-929890.html

My question was:

Is IMAX B6 Lipo charger turns 12V into 220V like inverter or not?

it's a type of inverter ... it changes 12-14V to 7.4V
it will use a switching circuit inside as it is the most efficient way of doing the conversion

I see no problem using that unit ...
As with all things running off a car battery, it is always wise just to start the car up occasionally to avoid a flat battery
Dave

 

[jim hardy]

I think karabiner does not have a thorough grasp of the difference between power and energy.

Here's a snip from the Imax user manual at http://www.ittgroup.ee/files/IMAX_B6_manual.pdf

Comparing a 50 watt battery charger to a kilowatt automobile alternator is like comparing a sled dog to a Percheron draft horse.

Unless your car battery has reached end-of-life where it has lost 90% of its capacity, it will shrug off the little bit of energy your charger puts into the RC battery.
When the car battery approaches that end-of-life state it is just about to strand you someplace.
So when you notice that just a few RC battery charge cycles depletes the car battery, replace the latter.

my two cents

old jim

 

[OmCheeto]

Hello everyone,

I'm a RC helicopter enthusiast and want to fly in the field where there is no AC wall socket available for charging the helicopter's battery.

The helicopter's battery is a 7.4V 1500mAh Lipo (11.1 Wh).

My car's battery is 12.65V 74Ah.

There is a charger available for charging Lipo batteries called IMAX B6 which can use car battery as its power supply.

I just want to know that if I charge my helicopter with my car's battery (engine not running), does it damage the battery or the car?

Is it harmful?

How long do you fly your helicopter before it needs charging?

From my calculations, your car battery has a capacity of 936 Wh. (12.65 volts x 74 Ah = 936 Wh)
So charging your helicopter just once, tells me that is depletes your car battery by about 1%. (11.1 Wh / 936 Wh * 100% = 1.2%)
This tells me that you can charge your helicopter 84 times before your car battery is 100% dead.
And from @jim hardy 's graph, the charge time appears to be about 16 minutes.

11.1 Wh/8.4 volts = 1.32 amp hours
1.32 ah / 5 amps = 16 minutes​

Flying time + charging time = time between charges.

Since there are only so many hours in a day, the "time between charges" would limit the number of charges required per day.

So, my second question is: How long to you fly your helicopter each day?

 

[sophiecentaur]

If there is any chance that the car would be stationary for several days (say you were camping and flying) then you could risk leaving yourself with a flat battery to start the car with (and a damaged-for-life start battery). The solution is to do what Camper Van and Boat Owners do. They have a start battery and a 'domestic' deep cycle battery. For not very much money, you can get a Voltage Sensitive Relay, which allows both batteries to be charged by the alternator and which will, for instance, disconnect the domestic battery if it becomes drained, leaving the starter battery fully charged. There are more elaborate charging circuits. The alternative of two diodes, one for each battery, is not a good idea because the charging voltages are wrong but it does protect the start battery.
But the realistic calculations above could suggest that this is not a big problem as long as the user doesn't change his power requirements and then forgets that he will need to drive home later.

 

[Quandry]

Hello everyone,

I'm a RC helicopter enthusiast and want to fly in the field where there is no AC wall socket available for charging the helicopter's battery.

The helicopter's battery is a 7.4V 1500mAh Lipo (11.1 Wh).

My car's battery is 12.65V 74Ah.

There is a charger available for charging Lipo batteries called IMAX B6 which can use car battery as its power supply.

I just want to know that if I charge my helicopter with my car's battery (engine not running), does it damage the battery or the car?

Is it harmful?

Charging using the IMAX B6 will do no harm to your battery or your car. Discharging your car battery too far will limit the life of the battery. Although your battery is 74Ah this relates to a specified discharge rate, and for car batteries it is normally quoted at the 20 hour rate. So you can discharge your battery at 3.7 amps for 20 hours before it is dead (and that means DEAD). As you say somewhere, car batteries should not be discharged below 20% of capacity. That means 3.7 amps for 4 hours before fully recharging. If you discharge at less than the 20 hour rate, two things happen, The effective Ah of your battery will be greater, and therefore your 20% discharge will be reached later than calculated at the 20 hour rate. (e.g. a battery rated 75Ah at the 20 hour rate will be rated about 80Ah at the 30 hour rate).
However, the IMAX B6 is going to change a 7.4v Lipo battery at about 5 amps. This is discharging at the 14.8 hour rate so your effective Ah capacity of the battery would be significantly reduced. By how much, depends on the battery manufacture, but I would use 60Ah as a max. So, to use 20% of 60Ah at 5 amps you can run your charger for 2.4 hours before fully recharging it.
A battery in good condition will easily start your car at the 20% discharge level.