Model Boat Mayhem - Forum

Please login or register.

Login with username, password and session length.
Pages: [1]   Go Down

Author Topic: 12v SLA 7.5amp Charging AM I DOING IT RIGHT ??  (Read 4269 times)

ivorthediver

  • Guest
12v SLA 7.5amp Charging AM I DOING IT RIGHT ??
« on: November 29, 2008, 08:39:13 PM »

Being new to marine modeling , I am concerned about correctly charging my battery used in the model and the TX.

I have a 7.5 SLA 12v battery in my model which I am charging the night before I go to the Clubs Lake on Sunday am.
my charger states that it is a dual charger [6v/12v] and says the following:-sec:6v/12v  500mA6va[max]
Is this the correct thing to do as when I have charged it overnight it reads 14v on my multimeter at 7am ? ?
I have been told that the 12v rating on a battery is its bottom rate and the amount above this is the "Charge"
taken up by the battery during charging ....is this correct?
In my TX which is a DX6i I use a set of four 2900mAh  rechargeable AA batteries which display a graphic charging rate and turn off when fully charged
So far I have had no problems .....but am I doing it correctly {:-{
Logged

Mankster

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 770
  • Wheelerdealer
  • Location: London, UK
    • RC Model Submarines
Re: 12v SLA 7.5amp Charging AM I DOING IT RIGHT ??
« Reply #1 on: November 29, 2008, 08:48:13 PM »

That voltage sounds about right for a fully charged battery. Once you put and sort of loat on it expect the voltage to drop to little over 12volts. And drop further when your down to 50 capacity or so.

OMK

  • Guest
Re: 12v SLA 7.5amp Charging AM I DOING IT RIGHT ??
« Reply #2 on: November 29, 2008, 09:27:32 PM »

"Is this the correct thing to do as when I have charged it overnight it reads 14v on my multimeter at 7am ? ?"

Ivor the  diver? Neat handle!
14v is about right. But it also depends on your definition of overnight charge. Bear in mind that any healthy SLA would also register the same 14v reading with only just a couple hours of charge. Now since your charger is pumping out 500mA, and as long as your overnight charge = at least 12 to 14hrs, then yep.... you're doing the correct thing.

Just out of interest....
How many hrs usage do you get from your DX6i with those 2.9A rechargables?
Logged

andygh

  • Guest
Re: 12v SLA 7.5amp Charging AM I DOING IT RIGHT ??
« Reply #3 on: November 30, 2008, 02:38:08 AM »

7.5ah at 500ma = 21 hours for full charge
Logged

OMK

  • Guest
Re: 12v SLA 7.5amp Charging AM I DOING IT RIGHT ??
« Reply #4 on: November 30, 2008, 02:57:02 AM »

I met a floozie once who could hold her charge for 22 hours.
Logged

tigertiger

  • Global Moderator
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 7,033
  • Location: Kunming, city of eternal springtime, SW China.
Re: 12v SLA 7.5amp Charging AM I DOING IT RIGHT ??
« Reply #5 on: November 30, 2008, 03:55:13 AM »

I was on a charge once and looking at 28 days.

But i got of with 7b days ROPs (Restriction of Privelages), Army days.
Logged
The only stupid question is the one I didn't ask

Martin [Admin]

  • Administrator
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 19,090
  • Location: Peterborough, UK
    • Model Boat Mayhem
Re: 12v SLA 7.5amp Charging AM I DOING IT RIGHT ??
« Reply #6 on: November 30, 2008, 07:43:37 AM »

Grooooan! Don't give up your day jobs!
Logged
"This is my firm opinion, but what do I know?!"    -   Mayhem FaceBook Group!

Shipmate60

  • Global Moderator
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,272
  • You bark - I will bite!!!
  • Location: Fareham
Re: 12v SLA 7.5amp Charging AM I DOING IT RIGHT ??
« Reply #7 on: November 30, 2008, 09:48:43 AM »

andygh
The figures you quote would give the charging time for a 12v 10 ah.

10ah x 1/2 ah (500mah) plus 1

These times are for charging a fully flat battery, after using the battery you dont know what charge is left in it.
If the battery is still reading 12 volts I charge mine for about 10 hrs (onernight) and mine have lasted well.

Bob
Logged
Officially a GOG.

wombat

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 642
  • The view from the shallow end of the gene pool
Re: 12v SLA 7.5amp Charging AM I DOING IT RIGHT ??
« Reply #8 on: November 30, 2008, 10:19:26 AM »

Being new to marine modeling , I am concerned about correctly charging my battery used in the model and the TX.

I have a 7.5 SLA 12v battery in my model which I am charging the night before I go to the Clubs Lake on Sunday am.
my charger states that it is a dual charger [6v/12v] and says the following:-sec:6v/12v  500mA6va[max]
Is this the correct thing to do as when I have charged it overnight it reads 14v on my multimeter at 7am ? ?
I have been told that the 12v rating on a battery is its bottom rate and the amount above this is the "Charge"
taken up by the battery during charging ....is this correct?
In my TX which is a DX6i I use a set of four 2900mAh  rechargeable AA batteries which display a graphic charging rate and turn off when fully charged
So far I have had no problems .....but am I doing it correctly {:-{


14V is typical for a VRLA (aka SLA - though VRLA is the preferred term) as the terminal voltage off charge - typically it will relax back a bit (to maybe 13V) within an hour or so. Remember though that this is an off load voltage and the voltage output will be lower than that. 12V is the nominal battery output (in that typically the output is somewhere around 12V). The minimum output voltage is lower than that - you can typically run the things around the 10V mark if they are low.

At work we have batteries in a number of critical applications - we do not consider the battery to be critically low on charge until it hits  the 9V mark under load. However the level of discharge that you can tolerate depends on the load - you can discharge further on high loads than light one - if the rating of the battery is 7AH and you only draw 0.7A average under load, you can only safely discharge to 11V

The recommendations from Yuasa for discharge are:

Discharge less than 0.1C or intermittent discharge - Min cell voltage = 1.75V
Discharge less than 0.17C - Min cell voltage = 1.7V
Discharge less than 0.26C - Min cell voltage = 1.67V
Discharge greater than 3C - Min cell voltage = 1.3V

Note C is the 1 hour current rating for the battery - a 7AH batter has a C value of 7A (easy innit). For a 6V battery multiply the cell voltage by 3 to get the on load battery terminal voltage, for a 12V battery multiply by 6. For most applications this give the minimum on-load safe terminal voltage for a 12V battery of 10.5V. Any lower than that and you risk damage to the battery.

For charging, you are spot on with the charging current. 500mA is the charging current - the figure of 6VA refers to the nominal power consumption of the charger. It is the nominal Watt power draw of the units (though expressed in VA for reasons too complicated to go into here). The safe constant current charge level for a battery is nominally 0.1C - so your charger is good for batteries down to 5AH. For batteries below that the charge rate is a little high and you should be looking at a smart charger that switches over from constant current to constant voltage charging) to prevent overcharging (I suspect all but the very cheapest are). The charge time depends on the capacity of the battery and the level of discharge. If the battery on-load voltage is 11V you can assume 100% discharge - you will need the full charge time. If it 12.3V then you will need a third of that time. However with the charger you have there is no problem leaving the battery on charge for longer.

Hope that has made it as clear as mud

Wom

To trickle charge
Logged
The prat in the hat - www.floatingwombat.me.uk - Have look & say Hi

ivorthediver

  • Guest
Re: 12v SLA 7.5amp Charging AM I DOING IT RIGHT ??
« Reply #9 on: November 30, 2008, 02:08:09 PM »

WOW  {:-{
I think I should have stayed on at school another week or two!

Thank you fellow modelers for your replies and advice .....and for wombats thesis on the theory of relativity

I thought that my Dive Leader Exam was hard ...until now............No all kidding aside ......thank you very much I have a grasp of the theory and its practical applications now thanks to you lads....if I could only get to grips with not cooking switcher units in my model .......F.L.J..might forgive me..... there again may be not    :((
Logged

FullLeatherJacket

  • Guest
Re: 12v SLA 7.5amp Charging AM I DOING IT RIGHT ??
« Reply #10 on: November 30, 2008, 02:24:43 PM »

....if I could only get to grips with not cooking switcher units in my model .......FLJ might forgive me..... there again maybe not    :((

Dr Wombat has a theory about connecting wires........it's to do with their colour...........and it's very rude in its full version. I blushed....... :embarrassed:

I always  forgive people who a) grovel; b) throw money at me; and, best of all, c) Both. It's the Customs Officer in my dark soul, you know  8)

PMK is a very, very naughty boy who talks smut. I shall smack his legs when I see him  <*<

FLJ
Logged

andygh

  • Guest
Re: 12v SLA 7.5amp Charging AM I DOING IT RIGHT ??
« Reply #11 on: November 30, 2008, 02:28:40 PM »

Quote
andygh
The figures you quote would give the charging time for a 12v 10 ah.

Not on my charger Bob  :o

7.5/500 x 1.4 = 21
Logged

andygh

  • Guest
Re: 12v SLA 7.5amp Charging AM I DOING IT RIGHT ??
« Reply #12 on: November 30, 2008, 03:28:10 PM »

You've got me thinking now, I'll have to check it  :-X

OK this is what I have

Logged
Pages: [1]   Go Up