@jim-p, Why shouldn't batteries be put in parallel?
If they are different chemistry or something significant I can see one getting depleted 1st, but otherwise I'm curious. What might happen?!
There are always tolerances in the production process, so even items from the same batch may vary slightly. Or one may be a few degrees warmer than the other.
Suppose one is 9.0V and the other 8.9V, and connecting wire is 1milliOhm, do the math!
Please don't put words in my mouth. I made no such statement. How does your reply help @art210516
As @stitech pointed out one battery may discharge into the other, which is not good for a primary (non-rechargable) battery
Sorry @jim-p I did not mean to put words into your mouth. I don't even know what statement or words you mean.
You did say
which I believe is incorrect, even if an official Arduino page somewhere may seem to imply that.
The possibility of using the 5V pin as an input to power the Uno provides @art210516 with additional options. The caveat is that it must be properly regulated 5V. Anything over ~5.5V could damage the Uno.
Have a nice day!
Thankyou, and the same to you also!
What about powering it through the USB socket. From a USB power adapter, like a phone charger. Those things are pretty ubiquitous all around the world these days.
Or if the phone charger doesn't have a USB connector, as long as it's a 5V supply it can connect directly to the 5V pin.
In case of 9V PP5 batteries, the current between them will be a few mA at most (due to the high internal resistance of the batteries themselves). No problem there. It's the charging of a non-rechargeable battery that may cause problems.
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To save money on batteries, you need to spend a bit up front. 6 x AA rechargeable batteries, a plastic adapter to gang them together for 9v, and a cheap charger. Then you can recharge them over and over. Much cheaper than buying 9v batteries and it will have a much stronger charge.
Thanks for helping me understand why I should be wary of putting batteries in parallel to gain additional amp hours. I'll have to rethink my approach to avoid replacing smoke detector batteries as often...
Spit my coffee laughed so hard. Thx vash, HH.
Whilst AA or even AAA rechargeable batteries are a good idea be aware that they are normally (for NiMh) 1.2V ouput when fully charged.
There are the NiZn rechargeables which are 1.5V when fully charged which I prefer to use.
And if long battery life in deep sleep type applications is needed use the low self discharge type NiMh.
This is a long-standing dispute, @jim-p has a special opinion on this matter:
Yes, around $3 (I translated from R$ to $ so you don't have to, in R$, it's 5)
yep
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I'm thinking of using a phone charger, but the output of the phone charger is USB-C! I am unable to utilize it at all by that reason.
Try find an older android charger cable with USB Micro. From there wire cutter and stripper down the cable. Use your dad's meter and find the 5V and Ground. Most of those android chargers supplied at least 1 AMP.
Hope this helps.
But surely 1.2V is the "nominal" voltage? They are probably a little higher than that when fully charged.
I have found that, for any of the brands of NiMH cells I have (Enerloop, Duracell, even some ancient Maplin), even fresh out of the charger, are at most around 1.35~1.4V. So 4x that still comes to ~5.5V which I've connected directly to the 5V pin of Nano V3 without any problems. Maybe I'm sailing too close to the wind, because I have read that they can be, in theory, as high as 1.5V.
Out of sheer curiosity I’ve done some reading about NiMH batteries. I’ve seen voltages of 1.78v and even 1.8V as a limit at which the charging should be stopped. But there are other methods to determine the ‘battery full’ condition (dT/dt, dV, timers) so it is quite possible that one of these stops the charging earlier. Also it is stated that in a few hours after charging the voltage will drop to 1.4V. When in use the voltage should drop to 1.2V and stay there for some time, and one should not discharge further than 1.0V.
So, using 4 NiMH’s directly at the 5V pin might actually work. It’s not completely free of risk though.
There is more: sometimes the USB will be connected, and the batteries may be charged by the 5V pin. The current delivered by USB may be as high as 500mA, and that is probably too much for the batteries. This can easily be prevented with a diode (preferably Schottky, low voltage drop).
On the other hand, it is stated that NiMH cells can be kept at ‘maintenance charging’ at 0.05C. A resistor parallel to the diode can do that. Let’s try to determine the value of that resistor.
In this case ‘maintenance charging’ will not be current driven but voltage driven, the voltage delivered by the 5V pin being 4.6 to 4.8V. In case the batteries are empty (1.0V), the current must be limited. Assuming AA size, 1300mAh batteries, charge current max 0.1C = 130mA, the resistor is 5.6 Ohm.
Feel free to ignore this, I can’t guarantee anything.