Battery Charge Time.
Submitted: Wednesday, Feb 16, 2005 at 18:23
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Member - Jeff M (WA)
Ok here's questions for the Battery Gooroos.
I've got a 17 plate 770CCA starter and an 80amp/hr Wet Cell Deep Cycle.
Normally I only stay overnight and then move on giving my batteries good charges throughout a trip.
I am however going away this long weekend and will be camped up for a couple of days and my Modified Waeco Thermo Cooler is going to kill my DSB within the first day or so.
How long do I need to run the car for (70amp alternator, say no other accessories are running with a high idle) in order to recover the 17 plate starter from the start itself and then charge my DSB back up to a reasonable level?
I'm using an Arrid Smart Relay hooked up with 4G cable to the starter battery.
Another Question, once the batteries try to equalise (bout 1min after start when the relay kicks in) will that give the deep cycle a quick boost from the starter bat, if I keep doing this will it eventually flatten the starter by equilising the flat DSB all the time?
We will be doing some 4wding and exploring throughout the day say we will be getting some charge time, just wondering how much is enough....
Reply By: drivesafe - Wednesday, Feb 16, 2005 at 19:23
Wednesday, Feb 16, 2005 at 19:23
Hi Jeff M, first off if you can connect the fridge to your main battery overnight on the first night, you WILL NOT take the main battery down below a safe starting level. Next morning simply swap the fridge back to the DC and you have given yourself an extended operating time before you need to charge up.
There is two reasons for doing this, the first is the extended operating time, the second reason is that as you are going to be running the vehicle to charge the DC battery, now you will be charging the main battery as
well for no additional cost or time. It’s just as easy to charge two batteries as it is to charge one.
Even if you flatten the DC both batteries independently decide how much charge current they will individually take. The higher the charge voltage, the higher the current intake of each battery.
At very worst, the two batteries will take a maximum of 50 amps ( 25 each ) for a very short time, only a few minutes and after this they will progressively drop back to around 10 to 15 amps each.
The longer you charge them, the lower the current draw is as the batteries charge voltage rises.
As to how long you have to charge them is up to how much charge you want in them. They will receive the bulk of there charge in about 1 to 2 hours but even this will also depend on how low the batteries are when you start charging them. It the old story, how long is a piece of string.
As for the batteries equalising, while your vehicle is running, the voltage level of the alternator is going to be at least a volt higher than either battery so the only voltage flowing into both batteries will be from the alternator.
You will need to have the engine revs at about 1500 rpm.
All up it would be better to just go for a drive.
Cheers
AnswerID:
98717
Follow Up By: Member - Jeff M (WA) - Wednesday, Feb 16, 2005 at 19:35
Wednesday, Feb 16, 2005 at 19:35
Cheers drivesafe, it's a good idea about running off the starter, however I feel that it would not have enough charge left. My cooler is a very thirsty evil beast. It draws about 6-7 amps for 40 minutes an hour and I fear that if I left it running off my start battery it very
well would kill it overnight. Not to mention the logistics as everything in my car is wired up to the DSB through an aux fuse box meaning there is no connections that I could draw of the starter with. I could always take one of my battery clip to ciggy lighter adaptors and hook it up that way though I spose, but I still reckon it'd munt it.
But a couple of hours is not so bad. I reckon we'd have to do a couple of hours a day anyway so it might be ok. WORST case I can always run the car with the idle up on for a while.
Thanks!
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Follow Up By: drivesafe - Wednesday, Feb 16, 2005 at 20:17
Wednesday, Feb 16, 2005 at 20:17
Hi again Jeff M, before you go away, try hooking your fridge to your main battery and just keep an eye on the voltage.
Let the fridge run until the battery is down to 12 volts.
First off, this is the lowest you can go but still have heaps to be able to start your vehicle.
Second, running your fridge off the main battery like this, I would be surprised if you couldn’t get at least 12 hours out of you main battery and still have heaps to start the vehicle.
Just a suggestion, cheers
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Follow Up By: Member - Jeff M (WA) - Wednesday, Feb 16, 2005 at 20:23
Wednesday, Feb 16, 2005 at 20:23
You reckon I could draw 6-7 amps from my starter for 12 hours and still have heaps to start a turbo diesel? That doesn't seem to add up... But I might experiment and see how long I can get, maybe a few hours... The surf seems to be a thristy starter, it used to run both batteries for starting and didn't appreciate getting dropped back to one. That's why I bought the 770CCa unit.
I've quite happily started 4.2TD patrols off my battery using truck jumper leads and they seem to "sound happier" starting than the surf does... Perhaps my starter is getting tired...
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Follow Up By: drivesafe - Wednesday, Feb 16, 2005 at 20:48
Wednesday, Feb 16, 2005 at 20:48
You can easily start any vehicle off a battery with only 12 volts and being as your battery is a decent size, yes I’m sure you will get at least 12 hours out of it, BUT I suggested you do this before you go away just in case it does flatten the battery, and you can recharge it without being stuck in the middle of nowhere.
I’ve been supplying dual battery charge controllers for over 15 years and many of my customers tell me they get up to an additional 24 hours out of the batteries by doing it this way.
And as you are going to experiment, don’t forget to let us all know your results.
Cheers
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