Connecting 12V & 14V batteries??? Good idea??? Bad idea??? Awaiting a Crater?

[Clifford]

Thinking about Electric Vehicles (still a little short on my generating capacity to get one).

Say, if one ran a rather high Ah "fixed" charging station on a battery bank at 14V (15V or so fully charged).  

If one had a 12V battery at 80-90% charge, the 14V system would pull it up to 14-15V which wouldn't be bad for the final 10-20% charging.

However, if one plugged in an EV with a 12V battery at 30-50% charge (say, 10.5V), then one would get a lot of amps flowing as the 14V system would struggle to pull the battery up to 14-15V.

Is it a good idea or a bad idea?

Is one likely to end up with a puddle of lead or a crater in the ground?

Is there a good way to make a DC Current limitor?  Add some large resistors?

Maybe create a shunt with a selenoid for auto-shutoff when nearing 100% charged.

Anyway, just an idea.

[Nando]

What is your idea, REALLY.

What are you trying to imply,

I ask because your question seems to have "deeper" and I mean "deeper" ulterior motives and I observe a lack of electrical/electronic knowledge.

If charging batteries exist, for electric cars, the arrangement would be to have a current limiter as defined by a keyboard or something that tells the charger to limit the current to certain level.

For electric cars, is logical that the charging plug to the battery bank will inform the charger to limit its current to a maximum and from there down as it is charged, also, I would expect to have a temperature report to the charger for the same purpose.

Addition of a resistor is quite illogical for such purpose, home "projects" have the tendency of NOT installing the proper arrangement BUT what is easy and cheap, as well as, to "heat" the environment.

Nando

[Opera House]

My sentiments exactly.

[Clifford]

Yes, my electrical knowledge is just deep enough to get me into trouble.

The goal would be to keep circuitry simple, and thus elimiate potential losses.  And, many (small, but significant) losses occur with changing electricity from one power form to another.

For example, there would be no sense taking 12V and sending it to an inverter to make 110V, then sending it back through a second inverter to make it back into 12V again.

Obviously there are both risks and benefits through simplified circuitry.

It is not uncommon to do the final stage of charging at 14V or so...  so I was thinking of utilizing that in the charging system.

Perhaps it will take a little more research.

Another option might be to utilize a 2-stage charging system.

1. st stage (discharged):  12V --> 12V.
   
2. nd stage (90%+ charged):  14V --> 12V.
   
   

I believe that I could make a disconnect based on either time, or (low) current flow.

[nailed]

I want to say something...  

Hmm my mom once told me if you can't find a nice way to call someone a dumb ass then don't say it.

Don't use a 14 volt charger or a 14 volt battery with your 12 volt stuff.  If it was made or a good idea I think some one would already be doing it and you would be reading about it.  

But if you do want to use some 14 volt batteries with 12 volt batteries all you have to do is get a big lag bolt and run it in to the next to last cell.  Use the lag bolt as the connecter stud.  Then hope like hell you did it right.