Pete,
It’s the other way around, Lipos are not as safe but have better performance. I normally run a LiPo battery pack wired in series for my RC Car. It is permanently soldered together, so it is safe, but isn’t what you said about wiring a charged battery to an uncharged battery in parallel true for any type of cell?
Yes, “any high-current battery…” I think is what I said above.
I could be wrong, but I was thinking that LiPo’s do not have the “puncture” danger of LiIon’s (i.e., when you puncture the case, it can explode).
Pete
Follow-up:
A quick check on the all-knowing Web says that I was basically correct.
LiIon gives somewhat better performance, although LiPo’s seem to be catching up.
There are more “hazard” warnings associated with LiIon’s.
Another advantage of LiPo’s is that they are more easily made into shapes that are not round.
Maniac05: You mentioned running “a LiPo pack wired in series”. Did you mean to say ‘parallel’? Putting them in series isn’t much of a hazard, except for the risk of deep-discharging one of the cells (which isn’t dangerous, but ruins the cell).
If you are charging them in series, then you probably shouldn’t, because the cells will not necessarily charge equally, and you may shorten the life of one/both cells. In factory-made packs that contain cells in series, the charger circuit has connections between each of the cells, so that it can ensure that they are all charged correctly.
Pete
You should always charge your batteries in the same configuration that they are discharged in. Not doing so is improper cycling and will shorten the life of the cell.
Yes, I did thanks.
I have a Lynxmotion biped (12 HS5645 Servos) which I would like to run first on a teathered lead to a bench power supply, and then from LiPo Battery pack onboard - I have not bought either the bench PSU or the Battery yet (only just got all the servos)
The question is how much current at 6V do these robots use on average?
The PSU I have seen can supply 3A, and I guess LiPo batteries are around 3600Ah…
Thanks
Well, if you haven’t read the first page of this thread, do so, as it parallels your inquiry.
From what the others say, it seems that 3A would be fine, under normal conditions, for your biped.
Myself, I used a 1600mAh NiMh pack (the one from Lynxmotion) and never had any problems with my Biped Scout.
I got about 45 minutes of play on a full charge with these.
Be sure to use a fuse with your power supply, though.
There’s the slim chance that the servos may overdraw the PSU’s max output, once in a blue moon, and I don’t think that we’d like to find that out the hard way.
As for the LiPo’s, you’ll need a voltage monitor or low-voltage cut-off to protect them from draining too much.
Lipos scare me… 
Hello!
just a quick question: i am totally new to robotics. i am planning to use my old pc power supply fuer developing process (read: testing, trial and error 8) ).
can i use the 5V for for the logic?
can i use the 12V (regulated with 6 volt regulator MX-05) for driving the servos?
should i consider a fuse (one for logic and/or one for servo power)?
I am concerned about the amps of my pc power supply: i dont want to burn anything.
Platform will be a SSC-32 and a Basic Atom Pro.
any help would be appreciated!
Thank you
What you describe is probably fine. And yes, put a fuse on the servo power (I don’t know what the best value would be - perhaps 3 or 4 amps?).
How much current is the 12V side of the supply? If it is not enough, consider using the 5V to run the servos, and regulate the 12V down to 5V for the logic. Or, just run everything from the 5V (it will have plenty of current).
Also, it may be possible to adjust the 5V output to be closer to 6V to run the servos on. But don’t attempt it if you’re not knowledgeable enough about power supplies (and the dangers).
Pete
Jones its entirely possible. I actually have already done it. The cool thing about AT power supplies is that you can adjust your voltage some what depending on the loads you have permanently connected to your 5 and 12v rails. Currently I have my PS set up just for 5v but have had it as 5.98v(basicaly 6). The trick is just to make sure you have enough of a load on each of the rails or else it wont work properly. And fuses are a good idea but as long as your careful you shouldnt need them. If there is a short, the PS should turn itself off. You can see a pic of mine here image61.webshots.com/161/0/21/41 … uzR_ph.jpg
Be careful there - a PC supply puts out 20A or more at 5V. A “short” could easily not exceed 20A, but still melt some wires (literally). Also, the supply will probably turn itself back on automatically.
I’d use a fuse, they’re very cheap and reliable…
Pete
Hello!
and thanks for all thow answers 
i will go for a 3-5A fuse and put it between. My actual output of the power supply is 5.15V
the link does not work… can you send me the pic by email?
thanks
My PS 5v rail cant exceed 6amps which is why I never fused it. It depends on the supply and the application but in your case, as suggested above, you would want to fuse it.
And about the pic, just go to my webshots gallery. The pic is under the random stuff album.
hmmm…
i finally got there: my hexapod is assembled, and i am developing moving gaits.
however: my power supply seems to break whenever i move more than 3 or 4 servos. i cant really measure the voltage output because my measure unit is to slow.
The effect is, that the servos do a short movement and then they suddenly stop.
i tested a 7.2vdc/3000maH battery pack and everything fine.
My question is: how can i get my PC power supply to spend some more amps? i already attached an hard disc to it, but that brought no success.
You could try putting a large cap across the power supply lines. The effect would be that it acts as a “reserve” to give you more current capability for a short time.
However, note that when you first turn on the supply, it will have to provide high current (briefly) to charge up the cap, so it’s possible that your supply will cut out. Most supplies automatically ‘restart’, so it should end up OK - on the 2nd or 3rd attempt, the cap will be charged enough.
Pete
thanks for the suggestion, pete.
i am not very experienced with this. what cap do you suggest?
or should i simply put some resistors across the lines to “fool” the power supply that there is need for current?
if so, how much ohms need to be placed?
thanks
First, I should mention that the “capacitor idea” is not guaranteed to solve your problem.
It may be that there is a problem with your power supply, or it is just a cheap/poor design.
Regardless, my idea would be to use a large-value electrolytic cap connected directly from +5V to ground. This type of cap is polarized, so you must pay attention to “which end is which” - you need to connect the “+” side to the +5V. Many caps will mark the “-” side, and not the “+” side, so you won’t always be able to find a “+” marking.
As for value, you want the largest that you can put your hands on. A good choice would be 10,000 uF or 20,000 uF if you can find one. But if you are buying at a place like Radio Shack, you may not be able to find more than 1000 or 2000 uF.
The voltage rating of the cap must be at least 7 or 8 volts. Typical caps will be rated at 10V, 15V, or more; any of which is fine.
Just putting a resistor across the 5V lines will probably make things worse - it sounds like your supple is already having trouble putting out enough juice. It’s possible that putting a bigger load on the 12V lines would help, but a disk drive or whatever would normally be enough…
Another idea for your problem is to run from batteries all the time, but have those batts connected to a charger at the same time. Much like the way the battery in your car really runs the lights, but the engine keeps the battery charged. Don’t just ‘hook this up’ without considering what type of charger and batteries you would be using - we can discuss further if needed.
Pete