AA Batteries in paralell

I am going to put some AA batteries in series/parallel. 3 AA in series (4.5v) in parallel with 3 AA in series (4.5v) giving 4.4 volts but increased mAh.

Should I incorporate diode/s to stop one set of batteries passing charge over to the other, or does that not happen?

Go back to the beginning.

Why do you need to parallel AA batteries in the first place ????

I agree with @srnet, you need to roll back for proper help. However, the lower voltage is probably because one of the six (?) cells is bad. Or at least worse than the rest. The thing to look out for for battery arrays is always if all cells are in the same condition weather they are rechargeable or not.

Edmunds

@ZOR - no simple diodes! [think of the voltage drop] Next why not use some C or D cells? If all the AAs are the same brand and date and used should be fine to do... anyhow be more specific what you are trying to do... why...

Thanks. I have not got any batteries yet only thinking. The reason for making them in parallel is to increase the mAh. I may go for 2 sets of 3 batteries. It's just a convenient backup power source.

EDIT: Thanks premelec, I had never heard of C and D cell types, just looked at some (3000mAh), excellent

EDIT: Just read this!

The voltage and capacity of a 'C'-size battery depends on the battery chemistry and discharge conditions. Alkaline 'C' batteries can hold up to 8,000 mAh, rechargeable NiMH 'C' batteries can hold up to 6,000 mAh, and zinc-carbon 'C' batteries usually hold up to 3,800 mAh.

That will do me fine.

Crikey, it's too easy for us old folks to forget that some people have never seen an ordinary "torch battery" !

A Torch?, what's that? Is it a jumbo sized candle?

I had not come accross D cell batteries before. U2 batteries yes.
Must go now, the gramaphone needs winding up.

Having mentioned candles; it is quite incredible how much power can be packed into a lithium battery pack smaller than a household candle these days. We are talking self-contained packs here, 2Ah, 5V out, charge with a 5V USB mains charger, all for just a couple of quid. Go up to the size of a cigarette pack and it can be 5Ah or more. Well worth considering.

Forget that new fangled lithium stuff - go for #6 dry cells! [if you must go with Li consider they also can have lower self discharge rates as well as higher price- there's one in my RF enabled gas company meter that's supposed to last 10 years] - a quick search on Ebay indicates #6 dry cells [dead!] are being sold as antiques

Premelec: Thanks, however confused by the two contradictory statements:

1) go for #6 dry cells!

2) a quick search on Ebay indicates #6 dry cells [dead!] are being sold as antiques

Hippy: I had a quick look for the lithium battery packs you mention but do you have any links to battery and charger. I have been treading carefully on these battery types with the publicity around them of fires and exploding. In addition reading about cheap Chinese batteries being risky.

If you have an old laptop battery then you can dismantle it. In it, regardless of its shape, you will usually find a number of 18650 lithium ion cells. Buy a suitable charger (single and quad cell versions exist, probably others). Then you get 3.7V at a high capacity, for free. You can also buy low cost torches, headsets, bike lights, etc with leds that use these, and are far brighter than normal AA-type units.

There is no risk of fires etc when discharging in an led torch or simple electronics setup. When charging, use a designed-for charger and that will take care of the voltage and current limits (which are severe but easily managed by electronics).

If you discharge them below 2.5 volts the charger may refuse to recharge, but if you have many free cells you can afford to lose a few.

http://www.amazon.co.uk/JB12-Portable-Mobile-Devices-1200mAh-Black/dp/B00NWKZCNK

That is the same brand and model as I have. Have performed perfectly well in the tests I carried out. I charge them by plugging them into a 1A USB mains plug PSU.

These are consumer items, include short circuit, charge and discharge protection, seem to be legitimately CE marked.

@ZOR I have used some OLD lithium cells from laptop packs - some of them have very LOW self discharge and others not - so if you go that route better test - in any case it is apparently unhealthy for them to go below 3v or so with a load [not sure about self discharge].

Many thanks everyone.
I have been looking at the 18650 battery and the TP4056 charger. A question, can I leave a charger in circuit whilst using the output of the battery so that it maintains it's charge, or should one monitor the battery in some way and initiate the charger coming in when needed?

http://www.ebay.co.uk/itm/Micro-USB-5V-1A-Protected-Lithium-Battery-Charging-Module-LiPo-Charger-TP4056-/291355449287?pt=LH_DefaultDomain_3&hash=item43d62357c7

premelec said:

@ZOR I have used some OLD lithium cells from laptop packs - some of them have very LOW self discharge and others not - so if you go that route better test - in any case it is apparently unhealthy for them to go below 3v or so with a load [not sure about self discharge].

Click to expand...

If they've gone below 3V with self discharge then they've probably been left that way for a long time (which is a bad thing).

Even when a smart battery pack is not powering anything, that doesn't mean there's no load on the cells since power is required for the monitoring circuit. It is common for this circuit to be powered through the 'bottom' cells in the pack which results in those having a lower voltage than the others in the pack. Again, if they're at 1.5V then they will have been that way for a while and you can enjoy high internal resistance and astronomical self-discharge that makes an early nineties Ni-MH cell (in use today that is!) look good if you attempt to use them. The other cells in the pack may still be at 3.5V+ and still perform well.

ZOR said:

Hippy: I had a quick look for the lithium battery packs you mention but do you have any links to battery and charger. I have been treading carefully on these battery types with the publicity around them of fires and exploding. In addition reading about cheap Chinese batteries being risky.

Click to expand...

Hmm... yes it does happen. My neighbour three houses away suffered a lithium-ion battery fire late last year and they only recently completed the repairs to the property. They spent a night in hospital following smoke inhalation and the fire brigade visited all the houses in the road warning of the dangers of charging lithium-ion batteries. I usually charge mine in the stainless-steel protection of a kitchen sink, just in case. The problem is that we have so many of these devices around these days. I note that the instructions for the pack that Hippy refers to states; "It is normal for Juice Bank to become warm during use. Stop charging if it becomes excessively hot. " - and just how you spot the overheating when you are tucked up in bed whilst the things are charging is beyond me! The same sheet instructs; "Do not attempt to charge and discharge at the same time"- which answers another of your questions. More importantly, it continues; "In the unlikely event of a fire, douse the flames by submersing in water (e.g. a bucket of water)". Well, yes, we all keep a bucket of water nearby when charging Lithium Ion battery packs, don't we? Remember the problems that Boeing suffered with the Dreamliner and Lithium Ion battery packs which went into thermal runaway and caused substantial damage to several airliners.

Caution is certainly needed when designing systems around these devices. They are superbly practical when they work well, but a house fire is no minor event!

Thanks circuit. I still have second thoughts whether to go down this road. I saw an article on the web where they did a controlled nasty on a battery and showed it's thermal runaway until it exploded. I also saw images of how heating progresses internally to which there is no external clues it's going on. I don't want to have to be around gaurding the battery while it's charging.
Recent programs on TV show customs and excise doing swoops on people selling cheap dangerous batteries and chargers. Yes they are all cheap on Ebay, but are they 100% safe?

No answer came back on this, got side tracked.


I have been looking at the 18650 battery and the TP4056 charger. A question, can I leave a charger in circuit whilst using the output of the battery so that it maintains it's charge, or should one monitor the battery in some way and initiate the charger coming in when needed?

http://www.ebay.co.uk/itm/Micro-USB-...item43d62357c7

ZOR said:

No answer came back on this

Click to expand...

Perhaps no one here knows or is not willing to make a definitive statement which you or others may later rely upon. No one will want to say "yes, you can do that" and then find out they were wrong.

To give a definitive answer would require knowledge of the field and an understanding of what is being used and how it is being used. The proposed use would need to be analysed. Given the risks when things go wrong that might not be an undertaking to be taken lightly.

The best option is perhaps to find a ready-built battery supply which is designed to allow use while being charged. If it is stated on that product that it can be used that way then it most likely can and the manufacturer should be able to answer any additional questions you may have.

Thanks hippy, I reposted it because two posts came after the question and thought it would get missed.
Yes I think you are right, and knowing what could go wrong with these batteries it's probably better to say it best not done unless out in the garden under a bunker.

As a side note, for the battery challenged types there is always Battery University a very good collection of information on all sorts of batteries. Worth a bookmark anyway.

Ron

Thanks for the link, that looks a very useful site, bookmarked it. Regards