Charging a car or lawn tractor battery off of my setup

[Sunking]

So I gather that if I want to do this, I would need to disconnect my bank and connect my charge controller directly to the discharged battery?

Yes that would work, should not take more than 3 days

Probably easier to just use the generator. Are there chargers that take a 12v (or 14v while the array is charging) input? Is there a device I could get to perform this operation?

A generator with a good automotive fast battery charger is the best option period.

Assuming the generator is at least 1000 watts or larger, you would want to have a large as a 12 volt battery charger as possible. By large I mean 30 amps or higher. The higher the amps, the faster it will charge. Here is why, it is simple math. You typical SLI car/truck battery is 60 to 90 AH capacity.

Amp Hours = Amps x Hours
Hours = Amp Hours / Amps

So if you have a 60 AH battery, and a 30 amp charger it will take 60 AH / 30 A = 2 hours. If it were a 60 amp charger than just 1 hour.

[bcroe]

Letting a starting battery get discharged and sit a long time is a great way to destroy it. Here such batteries (backup
generator, etc) are on MAINTAINERS, which feed a small current to keep them in a good state without overcharging.
They are not for charging a battery, the appliance does that when it runs. You need a solar powered maintainer setup,
designed so it draws no current when there is no sun. The smallest ones on the market were too small for me.
Bruce Roe

[SunEagle]

You can use your solar pv system to charge the car battery but it may not do it quickly enough depending on how much it has been discharged.

A solar charger is just that. It expects power from solar panels and not another DC power source.

Always remember is takes a charging source to produce about 15 volts to charge a 12volt battery. That is why a 12v battery will not work to charge a 12v battery.

There are manual generators that are attached to a fixed bicycle. They are called Peddle Power. Bikes I do not know what the output is from the generator but that may be another way to get those small lawn tractor batteries charged back up again.

[Basketcase]

So I gather that if I want to do this, I would need to disconnect my bank and connect my charge controller directly to the discharged battery? Probably easier to just use the generator. Are there chargers that take a 12v (or 14v while the array is charging) input? Is there a device I could get to perform this operation? Here is why a solution to this would be good. This is on an island with no power. Just off grid solar. There is one truck on the island so jump starting it from another car is not an option. We deliberately purchase only manual transmission vehicles so we can push start them if we need. We buy a new $500 truck every 10 years or so. It gets used very little. More common is a dead lawn tractor battery and we all know that the charging systems on mowers are not meant to charge a dead battery. For these reasons it would be really beneficial to have a separate "charging station" for other types of batteries. If my array can bring my other battery bank up to voltage, I dont see why it cant do the same for a car battery. I just need to figure out how to do it safely. A current limiting charging system of some sort would be perfect. Something that would allow the battery to charge slowly. I suppose one option is to use an inverter and a plug in charger, but I feel like that is not the most efficient way to do this.

[Sunking]

Won't work worth a darn, but a good way to start a fire if you are cold. It can be done, and can work, but beyond DIY capabilities. Screw up and you will have a fire on your hands or an exploding battery.

Now they do make Electronic Battery Isolators for boats and RV's that have an Emergency switch so one can charge the vehicle SLI battery from the House battery to get you going.

Never mind, I edited out how to make it work. To dangerous.

[jflorey2]

Hey all. I have a small off grid setup at my camp. I think the array is around 200 watts and I have 2, 6v 230AH golf cart batteries in series and I run phone chargers and a few led lights with it. Occasionally it would be nice to be able to charge a dead car battery or lawn tractor battery without having to fire up the generator (which has a 12v charge output). Is it against the rules to just use jumper cables to hook up a battery to my bank for charging and leave it for an hour or so?

Nope. As SE mentions it won't do a good job of charging those batteries, but if your goal is to jumpstart the car that will work. WARNING - if you go battery to battery you will have no protection at all, and if you short the cables you will do a lot of damage. It would be much wiser to jump from the downstream side of the fuse to the battery to be charged.

[SunEagle]

It would not be a smart idea to charge a car battery from your solar battery system. First off you will need about 15volts to charge that car battery and you only have 12volts in the solar battery. Even if you had a higher solar battery voltage (24v or 48v) it would still not be a good idea to use them to charge a car battery. It would quickly drain them.

Best way to charge the car battery is to get it started and let the alternator do the rest. You can do that by jumping from another car or use the generator and car battery charger to get it high enough to restart the car.

[Basketcase]

Hey all. I have a small off grid setup at my camp. I think the array is around 200 watts and I have 2, 6v 230AH golf cart batteries in series and I run phone chargers and a few led lights with it. Occasionally it would be nice to be able to charge a dead car battery or lawn tractor battery without having to fire up the generator (which has a 12v charge output). Is it against the rules to just use jumper cables to hook up a battery to my bank for charging and leave it for an hour or so? My instincts tell me NO but I can't find any info on it when I search. My thoughts were that if it is really discharged, it would try to pull a lot of current from my batteries and cause a problem.