Multiple batteries in a car.

[RicardoCervera]

Hi.
I'm trying to work out how to use a car as a power station, i got an old diesel rust bucket that is not road legal anymore but still runs, my plan is to add 5extra batteries and turn the engine on only to recharge the batteries, now, i know i need an isolator to keep the car battery separated from the other 5 my questions are!:
- Can i charge all the batteries without any modification to the alternator?
- Can i distribute the power from the array into the farm?, i know it will be 12volts but the current will be great and the only reason i wanna do this is coz it will be easyer to then use and inverter to a specific device in the farm "fridge, tv, etc"
- Most important, i wanna make an auto on and off switch to start the car when the batteries are down and full.

Before all the questions in why!?!?, my friend has a lovely farm house every time i got there is something that needs fixing but the main problem they keep on having is power, i though in turning a useless car into a power generator but a 240volt alternator will cost me alot and the car will have to be running 24/7, batteries seem like a good way to store and distribute the power.

Thanks.

 

[LightShow]

welcome to The EP

Can i charge all the batteries without any modification to the alternator?

with 5 Batteries it would be a good idea to replace the alternator with something more beefy and/or getting multiple alternators (like car audio fanatics do) so that the batteries charge faster

- Can i distribute the power from the array into the farm?, i know it will be 12volts but the current will be great and the only reason i wanna do this is coz it will be easyer to then use and inverter to a specific device in the farm "fridge, tv, etc"

you can allthough it would most likely cost more to get 4 guage wire to run than just getting an inverter. it also depends on how many things you are running and how far away they are.

- Most important, i wanna make an auto on and off switch to start the car when the batteries are down and full.

Maybe Someone else could help out with this? i would imagine you needing a microcontroller and sensors to detect when the car is out of fuel/ when the batteries are full

Regards, Lightshow

 

[HellasTechn]

now, i know i need an isolator to keep the car battery separated from the other 5 my questions are!:

Why you think you need to isolate them ?
With a much stronger alternator and the batteries in parallele you should be ok i think.

 

[bushtech]

As I understand it the problem with charging multiple car batteries with one alternator is that the alternator sees the battery bank as one battery. If one battery in the bank is at a lower charge than the others this drags the average that the alternator sees down and the alternator will keep trying to bring that state of charge up. In a worst case scenario with one stuffed battery in the bank the alternator will keep charging even though 4 batteries are fully charged and one is at a lower charge. The end result is then that the alternator keeps charging till the fully charged batteries swell and pop. You really need an intelligent monitor that monitors and charges all the batteries individially. Have a look at marine yacht installations.

 

[HellasTechn]

Car lead accid batteries are very tolerant in general. i dont think there will be a problem but 5 batteries are alot, what can i say?

 

[RicardoCervera]

Thanks for the reply.

I dont wanna do any modification to the car if i dont have to so changing or adding another alternator is last option.
The isolator prevents current being transfer from the car battery to the array, that way the array can drain but if i need to start the car the car battery will be top up.

Things that i dont know is that from the alternator has to be connected a rectifyer,then power to the car included a battery charger to keep the battery top up.

Would it be better for me to tap into the alternator directly with a multi battery charger.
I have seen but is not cheap a multiple car battery charger, the problem with this is that is plug to the mains so i will need an inverter to run it then i will need to made sure the inverter only use power from the alternator and not from the car battery!?.

 

[Wakoli Chokeli]

Why not get a charge controller for that case? That ensures that the batteries are isolated and monitored independently.

IF YOU HAVE PATIENCE AND SOME MORE CASH:
I suggest you modify the engine too. E.g adding a batter fly wheel, Removing the transmission system. You can as well use a custom dynamo which needs less torque but gives more current than the regular alternators(the type used in wind mills). Adding a toroid, and magnetic coupling instead of belt on the set up gives all the juice. On the lowest engine idle, you will have a super-gen. I did one before, costs less than a new gen and gave more power.

 

[Chemelec]

You can use Two Diodes to Isolate these batteries.
One Diode going to your Existing 12 Volt Battery.
Another Diode going to your 5 Paralleled Batteries.

But Chances are you will Over-Load the Alternator with the HIGH Current Draw and damage the Alternator.
NOT VERY PRACTICAL OR COST EFFECTIVE.

 

[RicardoCervera]

Why not get a charge controller for that case? That ensures that the batteries are isolated and monitored independently.

IF YOU HAVE PATIENCE AND SOME MORE CASH:
I suggest you modify the engine too. E.g adding a batter fly wheel, Removing the transmission system. You can as well use a custom dynamo which needs less torque but gives more current than the regular alternators(the type used in wind mills). Adding a toroid, and magnetic coupling instead of belt on the set up gives all the juice. On the lowest engine idle, you will have a super-gen. I did one before, costs less than a new gen and gave more power.

Hi.

I though about it, more like making a parking bay using 4 wheels under the rear axle so the car move it and then turn a fly wheel and in turn a dynamo as to mention but yet again this rig will have to keep the engine running in order to generate electricity, but is too much work for something that has to be much easier.

 

[RicardoCervera]

Thanks guys for all the replies.

I think i have to go back and rethink all this coz first i wanna use the car as a car, is a weather enclosure, if i remover the sits i can build a deck inside to arrange the batteries, i think i should use a second battery with an isolator and add a very big 12v battery then connect that big battery to an inverter to then power up multiple batteries chargers as needed.

Maybe adapting a PTO generator too.

 

[duke37]

Some comments.
1. A car alternator will not have the output you want.
2. The alternator should not be harmed by charging a very big battery.
3. Big alternators are fitted to trucks, tractors and busses, often 24V.
4. Some tractors have mains alternators built into the engine intended for driving auxillary machinery.
5. To charge one battery from a similar battery you need to provide about 2V boost, doing this via an invertor and mains battery charger will have considerable losses, use a boost circuit instead.
The alternator could charge the big battery and a boost convertor could use this to keep the starting battery at 13.8 to 14V.
6. The batteries MUST be well ventilated and free from any ignition source, they produce a mixture of oxygen and hydrogen when gassing. Do you like excitement?