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Old 12-09-2013, 09:51 AM
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pluto (Hugh)
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Quick battery charging question

Hi all,
I already have a 20Ah battery and a 3A charger. I'm looking at getting a new 85Ah battery and I'm wondering if I can use my existing charger or if I need a new one?
I don't mind if it takes ~30 hours to charge but I don't want to damage the battery?

Cheers
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Old 12-09-2013, 12:15 PM
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rogerco (Roger)
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Yes you can, it will of cause take longer to charge. How well it looks after the battery depends on what sort of charger it is. With the increased investment in battery capacity (particularly if a deep cycle type) it might pay to buy an intelligent battery charger if all you have is a basic one.
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Old 12-09-2013, 12:34 PM
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pluto (Hugh)
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Thanks Roger, it is a good quality charger and it's kept my current battery healthy so it'll do. Cheers.
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Old 12-09-2013, 12:39 PM
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naskies (Dave)
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The conventional wisdom that I've been repeatedly told is to use a charger of around 10-30% the battery capacity to preserve battery life. For example, for an 85 Ah you'd want a charger between 8 and 25 A.

I don't know how true or not this is. Aside from low-charge states being bad for deep cycle batteries in general, I don't know if there's something particularly bad about charging slowly.

If you do get a new charger down the track, it might be handy to keep an eye out for one with "power supply mode" that provides a constant 13.8V.
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Old 12-09-2013, 03:06 PM
alpharipper (Andrew)
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You are correct with that statement on 8 to 25a but should look only toward the lower limits, eg 8 to 12 Amps. 85ah bat will take approx. 10.5 hrs to charge at 8 amps. I personally wouldn't charge that size battery of any make or composition higher than 8amps.

Be very careful with AGM (Glass Matt0 and GEL batteries. If you charge with conventional chargers at high amps you WILL destroy the battery. Gel batteries will harden gel around plates and destroy it. AGM have there own set of issues.

The end note is if you do have a smart charger you will be fine, it will take a few hour to charge but it will do it safely and effectively, if you don't have one, I would avoid charging the said batteries mentioned above. The other important note is the output voltage. Different types of batteries require different voltage. Some charge between 13.8v - 14.2 standard lead acid and some require 14.8v.

Hope this help in your decision.


Quote:
Originally Posted by naskies View Post
The conventional wisdom that I've been repeatedly told is to use a charger of around 10-30% the battery capacity to preserve battery life. For example, for an 85 Ah you'd want a charger between 8 and 25 A.

I don't know how true or not this is. Aside from low-charge states being bad for deep cycle batteries in general, I don't know if there's something particularly bad about charging slowly.

**Some deep cycles (remember you get LEAD acid, gel, AGM) require bigger hits to get them up to 90 of full voltage then the charge backs them down for lower amps for the last 10 or so percent.

If you do get a new charger down the track, it might be handy to keep an eye out for one with "power supply mode" that provides a constant 13.8V.
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Old 13-09-2013, 10:19 AM
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pluto (Hugh)
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Thanks Dave and Andrew.
I'm thinking of this one from Jaycar: http://www.jaycar.com.au/productView...SUBCATID=998#3
it can switch between 3, 6 and 10amp, would 10amp be ok or should I look around for an 8amp?

Cheers.
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Old 13-09-2013, 06:39 PM
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acropolite (Phil)
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Hugh, that charger would be a good choice, gel or AGM batteries don't like being bulk charged when flat, that charger accomodates that need by trickling when flat before switching to bulk charge, as well as tapering charge as the battery voltage rises.
As a rule of thumb most Gel/AGM batteries will take a charge of C/5 in other words your 85 AH battery should be Ok charged at roughly 15 amps or less.

Last edited by acropolite; 13-09-2013 at 07:34 PM.
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Old 14-09-2013, 03:03 PM
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Thanks Phil
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Old 19-09-2013, 08:21 PM
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hotspur (Chris)
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Good to see an interesting thread on this topic,we do not see enough of this type of subject.Time and time again I see people come unstuck in the field on their trips,due to rather cheap looking chargers and poor battery set ups etc.

Its wise to pay the dollars and get the good gear,to save headaches and money.I bought this 'Projecta' charger-it was $280 well worth every cent=has read out,so you can see wwhats going on.change battery type,and anmount of charge-from very small amount to larger.Yes small/mid size amounts are better.I guess the full 25 amps would be if you really need car battery topped up in hurry-never used that setting.

See image for unit I have,I just purchased a 300 w sine wave inverter-Projecta brand too-was $260-but again better than those dodgey $120 from cheap shops-only going to bring heartache to those that buy those items.

Just my 2 cents worth.
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Old 22-09-2013, 06:16 PM
raymo
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I thought that I would add something to this thread that goes against
all the perceived wisdom.I am in my mid 70's, and have had all kinds
of equipment over the last 50+ years. I am long retired, and on a pension, and consequently cannot indulge in $260 inverters, $250
chargers, and $150 batteries, so I make do with what I can afford.
My Corolla's battery was 5yrs old and would not hold it's charge
while I was away for 2 weeks, so I replaced it, and now use the old
one for my scope. It has now powered my HEQ5 PRO GOTO and the
primary and secondary mirror dew heaters for almost 2 yrs. I get two
full night sessions between charges with my $25 2.5amp charger,
and the mount warns me if the voltage drops too low.
I do have a 200w inverter that I bought locally for $59 so that I can
run my laptop as well; but then I only get one night session between charges. My point being that less financially well endowed people
can find a way to run their gear without spending a fortune.
I ran my classic orange tube Celestron C8 off of an inverter for over two yrs.
[I paid $29 for it on ebay; the inverter, not the C8].
Happy viewing
raymo

Last edited by raymo; 22-09-2013 at 06:28 PM. Reason: forgot to say something
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