[h2k]

I am trying to create a 6V source via Sanyo Eneloop batteries. They are rated at 1.2V per the manufacturer, which would mean I need a 5 battery holder. But if I measure their voltage (right after charging), they are at 1.4-1.46V. This means that 4 batteries would be a better match.

What is going on here? Will they drop down to 1.2V after some use? Are there any concerns of not matching the 6V accurately? In other words, will it just not turn on if it is too high or too low or could it possibly be damaged?

 

[(*steve*)]

A lot depends on what you are trying to power.

You may be OK with 4, you may need 5, or for some purposes you may need 6 or 7 and a regulator (I think the last is unlikely).

What is it you are trying to power?

If it works with 4 batteries, go with that. Be aware that it might report a low battery indication sooner due to the lower voltage of these batteries.

 

[h2k]

I am trying to power a couple commercial units via batteries (instead of the AC-DC adapter it came with). One is a LED unit and another is a water pump.

I don't understand why the 1.2V rated rechargeable is reading 1.4-1.45V. That is the confusing part. It seems to work OK at 5.6V (4 batteries), but I am not sure it would work at 4.8V. I will watch it and see, but maybe it will normalize to 4.8V after some time/use and could there be a problem?

Would it be an issue if I put too much voltage on it (by going with an extra battery)? It would be more like 7V.

 

[(*steve*)]

Batteries have a discharge curve. The voltage varies with state of charge and load.

You should measure a new 1.5V battery one day.

It is almost impossible to tell whether the unit will be affected without specific information, and even then, you can only get indications.

In general, undervoltage is going to cause fewer problems than overvoltage.

Try it with 4 batteries and see how it goes. Compare the battery life between normal cells and the rechargeable ones.

 

[h2k]

From what I read, 1.5V alkalines have a discharge curve and can drop down considerably.

But I also read that NiMH are supposed to be fairly flat. So that is where I am confused. I was expecting 1.2V and fairly flat over the lifespan (as opposed to the much higher 1.45V after charging).

I will just check the voltage of the batteries as they age and see what I get.

 

[(*steve*)]

NiCad are usually rated at 1.2V, NiMH are generally rated higher. Most often they are a simple drop-in replacement for 1.5V batteries.

 

[h2k]

Sany Eneloops are 1.2V per the manufacturer...but this PDF explains it pretty well...see Page 5.

http://eznec.com/Amateur/1.5_vs_1.2_Volt_Batteries.pdf

Looks like after about 15 minutes, one can expect 1.25-1.3V at .5A load and 1.2V at 1A load. For a .5A load (my case), I would be about 5.2V nominal (4 batteries) and 6.5V (5 batteries). Hmmm...which is the better choice?

 

[h2k]

Based on those numbers, if I want a 12V source with .5A load, my best bet is 9 Ni-MH batteries (yielding 11.2-11.7V).

Sadly, you can only get 8 and 10 battery holder sizes.

 

[tryppyr]

Do what I did... build your own using single battery holders, or wired together combination of 3 battery holders.

 

[h2k]

I was thinking about that, but I want something that looks very clean and hopefully has a cover to enclose it. There are a lot of good options for 4 (AA), but less limited at 8 and 10..certainly no 9.

I was thinking about just getting a 10 and then just shorting the last one (to effectively get 9). That way it will still be pretty clean. If I can find an enclosed case, then it would be just fine.

Or maybe they even make "dummy" batteries that are just directly connected from + to -. Insert one of those and have 9 connected.

9 seems to work good since:
- at max voltage (1.45), the output is 13V. So not too bad over voltage.
- at .5A, 11.7V
- at 1A, 10.8V. At little low, but not too bad.

8 seems too low. 10 would work too, but it could be a little high when starting off? 14.5V max potentially. Though the nominal for a 1A load would be right at 12V.