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20th August 2018, 09:40 PM
#21
Patrol God
Originally Posted by
Clunk
Don't think the SBI12 would do the job, unless you disconnected the 2nd battery first
Easily a couple of days on the 35Ah battery... But to be honest I haven't actually seen how far it can go without being charged.
I feel a pack of winnie blues and some tests are needed
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Watch this space, as there maybe a comment added soon
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20th August 2018 09:40 PM
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21st August 2018, 10:28 AM
#22
So I did some more reading on this.
Ideally I'm wanting to be able to recover my battery from the load it supplied the night before, so I'd like to be able to recharge within 4-6 hours of driving the following day.
It seems the cpap machines use about 4 amps per hour, so during 8 hrs of use it would chew up 32 amps. Combine that with my fridge which at it's hardest uses 2 amps per hour, so over 8 hours it chews up 16 amps, I have a few lights but I'm not going to worry about them.
So I have 32 + 16 = 48 amps. If I can recharge at 10 amps per hour that will take me 4.8 hours to recharge which fits in my window. Is 10 amps per hour a realistic figure???
If I have a 100AH battery, that 48 amps will discharge my battery to almost the 50% level which is OK for AGMs, (but cutting it pretty fine) and not a problem for lithium.
Does that all sound correct or have I missed, overlooked or not known about something?
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21st August 2018, 10:38 AM
#23
50% depth of discharge is a heavy burden on any battery. Recharge of it will not be a problem until it reaches an internal resistance due to the constant flogging, and then becomes harder/takes longer to charge. This is my point from the first post. The alternator will easily recharge the battery in your time frame, but dragging it down so far will lessen its life, unless you go to a battery like the lithium perhaps, but I don't really know much about them to be honest regards DOD life span etc. I try to work on 15% DOD max for my set-up, and I get close to 10 yrs out of my deep cycles on that basis. It requires multiple batteries and extra weight, but financially I am in front. Food for thought.
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21st August 2018, 10:46 AM
#24
Expert
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21st August 2018, 10:50 AM
#25
Expert
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21st August 2018, 10:59 AM
#26
I am he, fear me
Originally Posted by
10G
snip...
So I have 32 + 16 = 48 amps. If I can recharge at 10 amps per hour that will take me 4.8 hours to recharge which fits in my window. Is 10 amps per hour a realistic figure???
If I have a 100AH battery, that 48 amps will discharge my battery to almost the 50% level which is OK for AGMs, (but cutting it pretty fine) and not a problem for lithium.
Does that all sound correct or have I missed, overlooked or not known about something?
Sort of... and depending on tech so below is kinda specific to AGM and constant voltage charger
AGM Batteries have what is called a 'charge acceptance rate' (CAR).
When using constant voltage charging (as opposed to constant current which is much more risky)...
The higher the state of charge (SOC) the less charging current a battery will allow.
This means a "10 amp" constant voltage charger won't deliver 10 AH from 50% to 100% and suddenly stop.
Sure it will punch in 10AH when the battery is down and up to about 85-90% but will start to taper off when the CAR drops below the 10AH available
Obviously this means you will need longer than 5ish hours to get back to full SOC.
This isn't a biggee really, it just means you will want a slightly larger capacity to ensure sufficient power.
You will still use the same power but from, say, 90 to 95% capacity as you most likely won't hit 95 to 100% SOC when out bush.
I would add about 15% to any calcs on battery capacities, charge rates etc sooo...
I would suggest 120 AH capacity and 6 hours charging @ 10 amps nominal or 100 AH and go for a higher rated charger.
Last edited by the evil twin; 21st August 2018 at 11:04 AM.
Dolphins are so smart that within a few weeks of captivity, they can train people to stand on the very edge of the pool and throw them fish.
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21st August 2018, 04:30 PM
#27
Thanks everyone for the help & advice.
Is it possible to charge a battery via a charger plugged into an inverter within the car?
My thinking is I have a 100AH aux battery and an inverter that runs off that. I could plug my charger into the inverter and charge my cpap battery as I drive.
I know that's a round about way of doing things, but I have 3 weekends before we go away so time is getting very tight to buy stuff and get it fitted in time.
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21st August 2018, 04:32 PM
#28
Expert
Yes I guess that would work also
I once tried to charge my battery using a battery charger and an inverter that was connected to that battery. It didn’t work lol
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21st August 2018, 04:42 PM
#29
Patrol God
Originally Posted by
Yeti's Beast
Yes I guess that would work also
I once tried to charge my battery using a battery charger and an inverter that was connected to that battery. It didn’t work lol
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21st August 2018, 04:45 PM
#30
Expert
Originally Posted by
Hodge
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I’m serious. Years ago camping on Fraser Island in summer with 4 young kids so hot as and raining.
My fridge battery went flat, the solar panels wouldn’t work so I grabbed my charger and inverter and tried to charge my flat battery
In my mind it was charging itself. Well it didn’t work. The charger wouldn’t switch on
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