You would need to break the connection between the +ve of one battery and the -ve of the other when putting them in parallel from series. And then break the +ve to +ve and -ve to -ve when moving them back to series from parallel.

If you connected them as both parallel and series you would short the batteries out, consider this schematic

(Probably not the best schematic ever but it was rushed) battery 2 is shorted to ground, therefore the voltage at any load is 0v and the spectacular explosion coming from the batteries would be quite the sight.

You would need to create a switching circuit to change the circuit from parallel to series.

However, in this schematic (again, not great but will do);

With switch 1 open and switches 2 & 3 closed you have a parallel arrangement With switch 1 closed and switches 2 & 3 open you have a series arrangement

Unless I have misinterpreted your requirements and you want battery 1 to power EZ-B 1, battery 2 to power EZ-B2 and a link between the 2 batteries to make them series (i.e. 12v) for charging, like this;

Which still wouldn't work. EZ-B 1 gets 6v but EZ-B 2 gets nothing since the positive of the battery is shorted to the common ground.

Do away with the common ground in your drawing Rich. Each battery can provide power to each EZ-B and still be in series to provide 12vdc for the charger.

Can you do away with the common ground?

And wouldn't Battery 2 still be shorting to ground (as in EZ-B 1/Battery 1's ground)?

Don't think so. As each batteries leads are extended to each EZ-B only the 6 volt potential will be present on each board.

Another way to test this solution is to place a voltmeter at the connection points of each battery. You will measure 6 volts on each battery but will see 12 volts when measuring from Bat 1 (-) to Bat 2 (+).

So far as the ez-b boards each running off of its own 6v battery you should have no problem. The batteries can be then connected in series to provide 12 volts to other devices. There are two issues.

The first is that you want to charge the batteries while they are in series. In this configuration you will by its nature create a cell imbalance between the two batteries. Each ez-b board will drain its respective battery at a different rate from the other one. Depending on cell type most manufacturers have warnings about the effects of charging systems and imbalanced cell batteries. This should be a concern.

The other problem has to do with the grounding and control of the 12v components. Only the ez-b that shares the ground with the 12v devices should be used to control the 12v devices. The other ez-b with the floating ground should only control 6v devices which share its ground connection or devices powered by the ez-b with the floating ground.

Lots of chances for releasing blue smoke and potential for shorting out a 6v battery.

This would not be my first choice for a setup.

Agree with @RobertL184 about battery balance issues. Grounding issues and running 12 volt components may create issues that can be cause for concern. My initial discussion was more of a tunnel-vision of the initial question and a solution using two batteries in series that could each power an EZ-B.

I'm not convinced that this would be the correct way to go about things, even doing away with the common ground. There is just too much scope for something to go wrong and damage batteries, controllers, accessories etc.

Is there any reason why the EZ-Bs would need 6v to them rather than the full 12V? As in, connect the batteries in series and power each EZ-B from the +ve of Battery 1 and -ve of Battery 2?

I orignially ordered two six volt and two 12 volt batteries because I was going to run an ITX motherboard. But, I have since decided to use a netbook. So, I really don't have any 12v devices except maybe the motors. Someone said that the motors run better with 12v. This is on the Omnibot.

What do you think?

I believe this was Josh's Drawing.

Personally I don't think that would work. I've only had a very quick look but when I get chance I'll trace out the schematic and redraw it so I can understand it better. But the link between the 2 6V batteries is linking Vcc and Ground together, trace it back it shorts across the + and - of the 12v charging source and across all batteries.

I see what you mean. That is why I wanted to check things out before I do it.

Anyone else can jump in when they are ready.

:)

The next question is: Can I use both of these 12volt batteries to power the motors with a 2.5 Amp H-Bridge?

If the motors can accept 12v yes.

It is the motors on the Omnibot2000 robot.

I usually have a common ground because of noise generated in the system. I am scratching my head on this one. The schematic seems ok, but then it doesn't.

Still confused. I may just hook all the stuff up individually.

confused

It's not 100% clear what exactly you are attempting to do.

If you use the sketch you posted most recently you will have problems, the 6v batteries are in both parallel and series arrangements which causes the bottom of the 2 6V batteries to short +ve to -ve which is not good. Removing the link will solve this but will cause the charging circuit not to function on the 6v batteries.

You need to either remove the link which makes the short or remove the links which put the 2 6v batteries in parallel and use them in series to make 12v.

A few options for you;

Option 3 can be simplified by drawing it like this;

I like option 3, but is it not shorted? it looks like the original drawing. It sorta looks like that ground is floating.

Thank You for all of your time spent on this.

:)

The last 2 schematics are both exactly the same circuit but drawn differently, both are option 3. There are no shorts, no floating ground.

Follow the circuit lines on the first schematic for option 3

The ground coming from Load2 joins the ground from Load1. The Vcc for Load2 comes from the same point that the Vcc for Load1. Bat1 and Bat2 are in series which creates a 12v battery, this arrangement is then put in parallel with the other 12v batteries since the +ve side of Bat1 connects to the same point as the +ve side of Bat3 and Bat 4. And the -ve or ground of Bat2 connects to the ground or -ve of bat3 and bat4.

Load 1 and Load 2 are both supplied with 12v.

It does make using 6V batteries pretty redundant unless you are planning to reuse some you already have. If you are buying everything to make this setup then you would be better off just using 12v batteries and putting them all in parallel.

Thank You, RICH!

:)