Charging my cars battery without a wall outlet

We have 6 cars but only 3 parking spots in the garage of our house. So I rented one parking spot very close to our house and another two (for my 512TR and 575M) in a large garage with about 50 other cars in 5 minutes walking distance.

So far so good. I drive my cars quite often so that I don’t need a trickle charger for any of the cars. During winter I don’t drive the 512TR because of the salt, so this car needs some charging of the battery. Since the next power outlet is quite far away from my parking spot I placed a long cable very nicely through the garage. You can hardly see it.

Now it comes: Somebody complained about my cable. I don’t know if they fear they have to pay for the power I use or whatever. So the company that rents the parking spots to me requested me to remove my cable.

Here is how I hope to solve that problem: I bought a separate battery and an inverter which converts the 12 Volts of the separate battery to 230 Volts (that’s what we have here in EU) to power my trickle charger. Well, that sounds a bit complicated to transfer 12 Volts to 230 Volts just to feed my trickle charger which transfers the voltage back again to 12 Volts. I did not found a better solution.

When I connected the inverter I found out that it draws 150 mA in standby (without feeding my trickle charger or any other device). So it would drain my 72 Ah battery in just 480 hours = 20 days. In practice this will be even less because I don’t assume to have the full 72Ah at 12 Volts over the whole time. So this may be 10 days or even less.

The solution to this problem is a clock timer. The clock timer only uses 2.2 mA which my battery should be able to feed for over 1000 days. So I plan to switch on my trickle charger once per day for 30 or 60 minutes to charge the battery of my car. Thus the battery should be able to feed the inverter for more than 2-3 months before I have to recharge it.

I just put it all together and put it into a box. I will try if it works during the next days.
Hope this help other people with a similar problem.
Any feedback is welcome.

Here some pics

Markus
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Yepp, that is what I would like to do as well. Unfortunately I don’t have any outdoor access from my parking space (it’s a large garage with more than 50 cars in it), so no sun somewhere near.

Markus

 

Thanks for your very good input!

I am not a trickle charger expert either but as far as I understand this should be OK. Of course the aim of the charger is to be connected over the whole time but when the battery is fully charged the trickle charger just monitors the voltage and if it is too low, the charging process starts again.

The inverter watches the input voltage and will discontinue to work if the voltage is too low. So this prevents the battery from a deep cycle. I guess I should be on the safe side here. And if not, I just buy another battery.

Yes, my 512 TR has a Motronic 2.7 as well which is much better than the 5.2 (or 7.2?) in my 575M for switching the power of and on again. You are absolutely right, I could just switch off the power (and maybe take the battery to my home). Last year I had my car on the charger for the whole time and felt very comfortable. So this is why I wanted to do it the same way.

Thanks

Markus

 

David

Thanks for the input!!

I am not sure if it is a good idea to hook up 2 or 3 batteries in parallel. If one of the battery fails I am not sure what happens to the others and if this could end in a dangerous situation. But I am no battery expert.

The inverter and the timer together were less than the battery. So that was not a big issue.

Plus I graduated as an electrical engineer (more than 25 years back) and I thought I had to do a little project again

Markus

 

This would be a too simple solution

And I already started my project, so I don’t want to go back…

Plus it is nice to be able to charge the 575M as well. And there it is no fun to remove the battery and to re-learn the Motronic after leaving the car without power.

Markus

 

For the money the components costs me I can fill up gas for 1-2 times.

 

Regarding clothes but nor cars. My neighbor once said to me: “I see, you don’t mind your old jeans as long as you can drive your Maserati and Ferrari”. And she was completely right.

Markus

 

I didn’t know you could keep the memory of the Motronic alive with a 9 Volt battery. Good idea. But there is the alarm system of the 575M too which drains quite a lot of power. So the 9 Volt battery would be empty after some hours I guess.

Markus

 

Thanks for your thoughts!!

Well, I don’t want to dispute with somebody who has two master degrees where I only have one

First of all, I already put my inverter together with the other stuff and I don’t want to go back (even if your solution would be the better one)

Secondly, I am not sure about the failure rate of the car batteries. We all know that they last for about 4-5 years and then you should change them. Even worse: If one of the batteries should have a short, this would drain the other batteries very quickly resulting in a nasty result. That’s why I don’t feel comfortable with this solution.
When I was young (well, I am 50 now), I was running a very large computer system. The system was highly fault tolerant having 5 power supplies in parallel where 3 or 4 of them would have enough power for the whole system. Guess what happened: One of the power supplies had a short resulting in a damage of all other power systems. The engineers thought they built a solution with a high redundancy but in fact built one with a much lower redundancy.

And as a last point: Maybe I have a much simpler solution. There is a new house with 24 garage spots very close to my garage. I talked to the owner and he is willing to have me installed my Ctek to the wall outlet. I will visit the spots next week and if they are OK I think I will move my cars to this garage. This would be the simplest solution.

But anyay, I have to find out if my solution really works. I just returned from my skiing Holidays and will install my Inverter tomorrow (I did not want to install it last week and then go off for holidays. If something would have happend I want to be around and not 200 kms away).

Thanks for all these good suggestions! I really appreciate them!

Markus

 

That’s exactly what I did. I found 3 spaces in a very nice underground garage. Power is no problem too since the owner of the garage has ordered a Tesla. He offers the little power I use for my battery tender for free and also offered me to come immediately into his garage where I have to pay for the spaces two months later (I still have to pay for my other spaces until the contract terminates).

The pic shows my 575M. I just moved the 512 TR as well into the new garage and still have a spare spot for another car…

It is quite a special garage since you have to enter it with a car elevator (see 2nd pic).

Markus
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It’s only about 2 floors (7 meters). The numbers are there to count back from 8 (or 10, not sure), that you see the elevator is moving. Very nicely done. The elevator is so calm and smooth you would hardly notice it is moving without the numbers.

Markus