Recheargeable Batteries: 9v vs AA

[mooeypoo]

Hey guys

 

The people in my workplace use a bunch of electrical utilities that is - currently - equated to a bunch of crap, due to mishandling and bad maintainance. Since I repaired a few malfunctions, my boss has decided to put me in charge on the equipment in general.

 

The problem is that my knowledge is limited

 

So. I must have some help, so expect a few questions from me in the next few weeks, months, years, however long it'll take to fix the pile of rotten metal to make it appear to be a functioning equipment set.

 

First order of business - Batteries.

 

We work with magnetometers and when I opened them I found most of them are using a pack of 7 rechargeable AA batteries (ranging from 600-800mAmp). One of these, though, used a simple 9v rechargeable battery. All of the connections to the circuit board are through a 9v-type connector, so I can basically switch the 7-AA pack to 9volt with no trouble, and vice-versa. Now it's just about choosing the right kind for the job.

 

The batteries are crap. They were mishandled, used only to half capacity and then recharged, and were last replaced when I was a toddler. We are in dire need of replacements. So we are about to buy a whole new batch.

 

Which is better to use in an environment of non-technical people? a 9v battery (that probably lasts for less but is discharged more and therefore lives longer..) or a pack of 7-AAs, lasting longer but will probably need a routine discharge/charge in scheduled amount of time...

 

Thanks for your replies,

 

Good to be back (and hope school will allow me to post here again more regularly!)

 

Oh.. and expect more questions about faulty equipment rigs soon

~moo

[mooeypoo]

Oh, sorry, another thing -- if I do end up buying packs of 7 AA batteries (which also cost more.. and apparantly that's an issue ) is there a limit to the amperage? basically as far as I know the circuitboard itself draws energy, so I THINK (not sure?) that the higher the capacity, the longer they take to discharge and therefore give out more output. But.. maybe I'm wrong.. I don't want to fry the circuitboard, or even the cute little fuse on it.

 

(I had to add 'cute' something... girlish touch).

 

thanks in advance,

 

~moo

[Rocket Man]

the fuse isn't a problem unless you mess up the voltages and feed it substantially more than 120% it's rating. which is hard to do with only 7 cells

a 9V is a set of six cells in a convineint case. you pay for fiddly manufacturing. each cell is 1.5V, that goes for most commercial batteries (except nicad rechargables which are 1.2v each).

 

pros and cons of each are in terms of life, cycle length, cost.

a 9V will have a REALLY short cycle length. some stage crews put a new 9v in a radio mic every performance, and they cost way too much up front.

a AA is a reasonably cheap type of battery, but they do run down quite quickly.

rechargables are different. if you buy a nice, modern set you'll probably have a longer cycle length than the life of the AAs. if you keep away from the NiCads and a few others, you should be safe from the "memory effect" which ruins a good set of rechargables.

[mooeypoo]

One of the biggest worries I have is the "memory effect" because the people that work with me just hook up the devices to the chargers without checking, and they're in general a bunch of spoon-fed bastards when it comes to equipment. That's why I thought about the AAs, actually, so that maybe i can replace them individually...

 

But... long term operation also is an issue, if we have double (and sometimes triple) shifts.

 

My boss was also thinking about putting chargers at some of the posts, so that changes the picture slightly too. If we charge a lot, maybe it's better 9V, but wherever we don't charge, the AAs are probably better...

 

Let me try another question, maybe that will tip the balance:

 

I am planning a routine weekly maintenance for the magnetometers and batteries in general. I thought about fully charging them at least once a week (I am almost sure they're not fully charged between shifts). If I am going to do that, and perhaps add a few 'routine' maintenance actions to the batteries (open to suggestions..), I assume that we can use AAs and extend their operation time for a few weeks.

 

Sadly, there's the issue of cost-effectiveness. That's why I'm trying to figure it out.

 

We're thnking of buying about 6 9v initially to test them out.

 

 

AAAAND Another question:

I only find 9v batteries with 200mAh. That's tiny. The only 1000mAh 9v I found are sold 2 for $15 which is expensive. Anyone knows of a place to get bulk ones?

 

Thanks!!!

 

~moo

[Rocket Man]

iirc, the rechargable alkilines don't have the memory effect

other than that, if you completely flatten the batteries before you charge them they last longer. i can imagine most devices have quite a high "dead" voltage so if you eventually go rechargable AA size, try to be creative about the use of the remaining power. if you're feeling generous, you could donate the dregs to the hamster that powers the forum, he deserves a break.

 

i think 9v size is going to be a huge waste of money even if you manage to buy in bulk.

800mA/hr ought to last a week depending on how energy intensive these things are. buy a pack of standard AAs to get cycle length, rechargables should last a little longer

[Cap'n Refsmmat]

I believe only Ni-Cad rechargables get the "memory effect"

[mooeypoo]

800mA/hr ought to last a week depending on how energy intensive these things are. buy a pack of standard AAs to get cycle length, rechargables should last a little longer

 

 

Yeah it's a magnetometer, it's using a fair amount of power for creating an electromagnetic field around the coil. Do you have any idea how I can check the output of the charge so I can plan what kind of batteries I need?

 

It seems, so far, that the AAs will be a bit better both powerwise and cost-effective wise..

 

I believe only Ni-Cad rechargables get the "memory effect"

 

And yeah.. I know I should avoid these at all costs...

 

Thanks!

 

~moo

[insane_alien]

i'd say go with what they were using already just make sure the batteries are in better condition.

 

good to see you back mooey

[mooeypoo]

Sounds like a plan.

 

Thanks!!

 

Good to BE back! I missed this place!

 

btw.. I was so pwned in a professional E.E forum, geesh.. I asked a similar questions and within less than an hour someone basically told me to go study, if I am not sure which option has more energy.

 

Agh. Professionals can be so condescending!

 

~moo

[insane_alien]

the one with the most energy will generally be the one with the most mA·h in it.

 

add them up and divide by the cost. which ever has the higher number go for it cause it will give the most energy for the money.

[Rocket Man]

they're in series so the mA/hrs don't add for the AA size

check how long the standard AA lasts as an indicator for that size.

then divide the cost per mA/hr by the number of effective cycles (i'd say a fifth of the advertised cycles considering your description of the users)

cost / (cycles * cycle power)

[mooeypoo]

WOW.. a fifth would mean us replacing it quite often.

 

This will be ideal, but I will have to see. I'm not the one deciding on the budget ... :\ but for now, we decided to buy about 50 AA rechargeable batteries to test out.

 

Also, we've split the electrical sockets to try and put about 8 2-way radios per socket (it used to be about 30 !!! and they were surprised it took forever to charge... ) and about 10 magnetometers per socket (would PREFER a lot less, but for now there's no other option, out of the limitations of the room and the number of sockets).

 

I hope that would at least increase the lifespan of the batteries and it would probably make the batteries operate for longer.

 

Thanks for all your help guys

 

~moo