Quick question about VIN on BOE

Ugha

Sorry for the newbieness of this question. I just want to check that
I'm right before I take a chance of frying my BOE (And the two BS2s
connected to it)

BOE-boost basically just ties in another battery to the battery pack.

Can I do the same thing with a two-AA battery pack fed into VIN on
the appmod header?

I think that'd give me 7.5 volts with six rechargables which shouldn't
be a problem for the BOE's on board regulator.

So to sum it up, by wiring a 2 AA battery pack to VIN and VSS can
I use six rechargables?

Chris Savage

No...connecting the batteries independantly like that will mean they are connected in Parallel and you will not get the results you want.

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Chris Savage
Parallax Engineering

Mike Green

No, you'll probably destroy the batteries when you turn this on.

Draw out the circuit that you get when you connect things the way you suggested.

I could describe what you've done, but you should be able to figure it out yourself if you diagram it the way you'd actually have it.

Ugha

Doh! Your absolutely right. I apologize for my stupidity.

Although I don't understand why it would destroy the batteries. If they are in in parallel wouldn't that mean its just
providing more possible current to the BOE and the batteries will last longer as a result? Or do I have that entire
concept wrong?

I'm having a tad bit of trouble figuring this out (poor imagination I guess). I can't visualize or draw out exactly how
the connection should go. If I connect to the BOE's battery pack in the same place that a BOE-Boost connects, would
that put all batteries in series or would 5 be in series and 1 parallel? Please excuse my lack of understanding.

Chris Savage

Paralleling 2 cells with 4 would not have good results.

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Chris Savage
Parallax Engineering

Ugha

Oh! Because it would try to draw the current from the 2 cells as if they were 4!

I feel so dumb [noparse]:)[/noparse]

So, if I had another 4-cell pack I could parallel them the way I said before (connecting to VIN and VSS) with the result
being that both sets of batteries would last longer and no negative side effects... right?

Although that still won't let me use rechargables.

Guess I'm asking my wife for a BOE-Boost this christmas [noparse];)[/noparse]

Mike Green

Paralleling batteries is usually problematic, particularly when they're not identical in construction or capacity. In your case, the 4-cell battery will attempt to discharge through the 2-cell battery. Since the current isn't limited, the 2-cell battery will heat up and there may be some chemistry-related damage as well inside the batteries. Depending on the size of the batteries, you could even cause a fire. On the other hand, rechargable batteries are often connected in parallel or series-parallel. They do have to be the same chemistry system and close in capacity. Connecting non-rechargable batteries in parallel will cause them to discharge into each other and a lot of their capacity will be wasted that way and turned into heat.

Never never parallel lithium batteries. Never attempt to recharge lithium batteries without a charger designed specifically for the batteries involved. They catch fire very easily when charged improperly or even discharged too quickly (like short circuited) and they produce an intense, dangerous fire.

Connecting batteries in series is much more common and works well as long as the batteries use the same chemistry system and are approximately the same capacity

Mike Green

I recommend making your own Boe-Boost. You can buy a single AA cell holder for $1 from RadioShack with attached leads, glue it to the BoeBot platform just above the ball, and wire it in series with the existing 4-cell AA battery pack.