Hi all! quick question regarding Lipo and NiMh batteries; Is it safe to power an Arduino using two LiPo’s in parallel and then also a NiMh battery in parallel? The two LiPo’s are 7.4v at 1000 mAh and the NiMh is 7.2v at about 3000 mAh. Is it possible or will it destroy the batteries and/or the Arduino? Thank you!!
I wouldn't advise doing that. While the nominal voltage mightbe close, the voltage of each battery chemistry is different for different current levels and state of charge. You may end up rapidly transferring charge from one battery to the other and over heating it.sora62896:
Hi all! quick question regarding Lipo and NiMh batteries; Is it safe to power an Arduino using two LiPo’s in parallel and then also a NiMh battery in parallel? The two LiPo’s are 7.4v at 1000 mAh and the NiMh is 7.2v at about 3000 mAh. Is it possible or will it destroy the batteries and/or the Arduino? Thank you!!
even if I put them in parrallel?
Because you put them in parallel !sora62896:
even if I put them in parrallel?
That .2 v difference would actually result in a short. That means intimate current running between the batteries, going over their current limit, thus killing the batteries.
ah…but in series it wouldn’t?
You would get uneven discharge since they are not the same type of batteries.
so I ordered a second lipo battery, with the same voltage but different mAh’s. I will be able to hook these up in parallel right? (The 3 LiPo’s)
Just remember, LiPo likes to burn if anything isn’t setup perfect.
I'd only every parallel IDENTICAL LiPo cells - as LePaul says, they can be very fussy.sora62896:
so I ordered a second lipo battery, with the same voltage but different mAh’s. I will be able to hook these up in parallel right? (The 3 LiPo’s)
so even if the voltage is the same, but current is different, I’m going to have a problem?
Potentially - whenever you parallel batteries (whether it's lead-acid, NiMh or LiPo), it's always a good idea to use identical types so that charge state and charge / discharge current will match.sora62896:
so even if the voltage is the same, but current is different, I’m going to have a problem?
what will happen if I put them all in parallel? Is it 1000% doomed from the start or will I get some time out of it until I can buy another battery? Let me give the specs so you can see how much of a difference there actually is–First, there are two 7.4v 1000mAh batteries which are in parallel already. There is also a third battery, 7.4v at 2200mAh. So if the 1st two are in parallel then hooked up to the third, what will exactly happen? Will it be something minor like the batteries lives will be shortened or something drastic like explosion and/or fire? I hope it’s just the first!!
sora62896:
…Will it be something minor like the batteries lives will be shortened or something drastic like explosion and/or fire? I hope it’s just the first!!
When you first connect them, a high current may flow for a short time until they equalise their internal voltages. This won’t cause a fire (you generally have to overcharge for some time for this to happen), but if you’re worried you can connect them using a resistor temporarily until they equalise.
As for their life being shortened, this will have a lot to do with how you discharge them (over-discharging, or discharging at a high rate reduces their life), as well as whether you charge them with a proper regulated charger.
Well what I see happening with that set up is that the 1st 2 will discharge faster than the larger… so when the voltage of the 1st 2 is lower, it will bring down the 3rd very fast. This causes lots of issues. Usually designers use a IC to connect the batteries in parallel to prevent this.
So as long as I watch the batteries’ voltages while I’m using them, I should be fine, right?
I am going to be using these with a robot I’ve built—just finishing the coding—and I needed a little more kick
so after each run if I balance the batteries, I should be ok, right? (if I’m understanding this correctly…)
Just get the IC that is ment to do it.
What do you mean IC? I’m not fully familiar with all of these terms yet…What is that exactly?
IC= intergrated circuit=those little black boxes on pcbs. (printed circuit boards)
If these terms are unfamiliar to you then I seriously suggest you start with only a single battery, of sufficient capacity (amp hours) and not a Lipo chemistry. Build up some electronics knowledge first before you risk setting up your robot/room/house on fire when it gets stuck in a corner. No offense, but the Electronics for Dummies book might be appropriate for you to get you started. Don’t worry, I’ve got one too here. 
If you plan to balance lipo discharges, then please read up on electronics, batteries, and everything of the sort. I say this for your own good; if you misdesign the circuitry, then your lipos could catch fire and explode. So please be safe and don’t do that.