I hate to be the bearer of bad news. But the power system you are wanting to implement is flawed from the start. It will never work, and here’s why.
The wires on the plastic battery holders are 28 gage. That gage of wire is only good for 1.4 amps.
The springs on the ends of the battery holders do not have enough surface area to transfer the current from the battery to the wires.
The typical alkaline AA battery has a capacity of roughly 3000mAh. But the efficiency drops dramatically as the current draw increases. At only 1 amp draw the capacity drops to 700mAh…
Your bot is going to need about 7-8amps of current when in operation.
Xan’s battery is 5 x Sub-C cells, not “AA” cells. They may not fit in the area the “AA” ones do on your bot. Also the concerns with the battery holders are still true even with the bigger ones. You really need about 20 to 18 gage wire to carry the 8-10 amps required. These would need to be soldered to the batteries as a complete assembly, or very good quality connectors would need to be implemented to make them removable separately. Not sure if the weight and complexity of the battery on a leg scenario is worth the effort. Just my opinion.
you may be able to buy single sub-C cells with tabs welded and then solder 18awg wire to the tab. ideally the tabs would have 4 or more weld points, and when you have the wire soldered to them then use some heat shrink around the cell and wire to hold the whole thing together… i.e. to minimize any stress from handling or vibration on the tab welds. These guys may be able to help you out with this as they build cusom packs readily enough. You’ll have to send them an e-mail though as it doesn’t look like their custom pack webpage supports < 2 cell packs.
My Lipo gives me 4900mAh at 7.4V. The home made batterypack used in BlackWido are 5 “AA” cells which I guess deliver 2600mAh. They are currently wrapped in so I can’t see the actual current. I looked at the website where I got them and the biggest onces they are selling are the 2600mAh versions… I guess I made a big mistake here…
Back to the problem, I think Jim has got some good points there. The same 7 to 7 Amps are running trough all the cells so you need big wires running from one to each other. Also the spring doesn’t give enough contact to carry the amps. But maybe it still is a good idea to stick with single cells since you can solder them together in any form you want. So you could build a more compacter pack.
so its advised that i solder the bats in series using 18awg wire. how would i get around charging them up or changing them without unsoldering?
would you say these would be ok.? dmcgaming.co.uk/product_info … ts_id=1420
EDIT:
what about adding a voltage reg or something to capture the current? is that pos?
You can solder a plug in there so you can plug it into a charger. Not likely to be fun to have to remove it for charging, but that’s just a drawback in the battery on a leg scenario.
I would run from those batteries as fast as possible. You will still have the problems actually getting the current from them as they have no solder tabs…
You lost me completely with the capture current question.
When any unwanted resistance is introduced into a circuit, the result is unwanted voltage drop. The full voltage from the batteries that should go to the servos, will be reduced. To the point of being too low to operate. So your servos try to “power up” they will try to draw more current than the contacts can pass and the bot will twitch and convulse.
i dont fancy watching that.
i will re-think my powering options.
what about taking out the springs and soldering thicker wire to the holder, and make some sort of plate for both ends of each battery for better contact? using 5 “AA” cells @ 1.2v 2600mAh.
Need more info. What size, style, and chemistry are the cells you are eluding to. So far we have discussed power distribution (wire size and connectors) issues, and chemistry (alkaline) issues. There already exists batteries that can supply the required current, so no real benefit to connecting two “AA” cells instead of a single sub-C cell for example.
thank you jim for your time on this. everyone has been a great help.
Uncharted territory is always a good step if done slowly. i will experiment about and see what i can come up with.
after all this i feel “discharged” oh dear! poor effort.
I knew they couldn’t be “AA” and have 4900mAh. lol I assumed they must have been Sub-C. Thanks for the explanation! 8)
