Looking for a 12 v dc "PowerPack" battery that produces A/C

[W. eWatson]

On 2/23/2012 10:17 PM, Winston wrote:

W. eWatson wrote:

(...)

I looked at the specs on the cpap. 5 amps!

That may include the humidifier.
When you get home, you can measure with an ammeter and be sure.

Found isolator at a local automotive store, 70A. $42.00. How does this
device
stop short of leaving enough power to start a car?

IMHO, it doesn't. From the little I've read, the 'isolators' are
just two heavy duty diodes mounted on a heat sink. Current from
your alternator connects to the anodes and the cathodes connect
to each of your batteries respectively, preventing one battery
from discharging the other. It's simple and clever:

Diode 1
.---->|------------.
.--o |
| | Diode 2 o
| ---->|-----. ( Auto
.---|--. | ) Fuse
| o | | o
| | | |
| | | |
| | Car | | CPAP
'------' Batt--- --- Batt
Alternator - -
| | |
=== | |
GND === ===
GND GND

(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de


Batteries Plus,a chain, has some batteries I think will help. The have
a store about 40 miles from me. I think I'll
finsh on this topic when I get back home in about 3 weeks.

Cool!

We pay more for ampere hours when they
are packaged in small (SLA) quantities as compared
to large (deep cycle battery) quantities....

Best of luck.


--Winston
I think my Fluke meter measures amps. I don't have a humidifier. My one

at home experience with the Xantrex and the cpap suggested pretty
convicingly that 5 hours was about the limit.

 

[Winston]

W. eWatson wrote:

(...)

I had a suspicion that a second battery might be used. Probably I would want the smallest battery I can find that would
provide several good kicks.

That is a good - sized battery.
Your standard 100 AH trolling battery would be good for only
about two day's sleep at 5 A drain.

'Course, if you can manage to recharge it daily, Bob's your uncle.

I think you require a less-hungry CPAP, practically no matter
what you do next.

--Winston

 

[Winston]

W. eWatson wrote:

(...)

I think my Fluke meter measures amps. I don't have a humidifier. My one at home experience with the Xantrex and the cpap
suggested pretty convicingly that 5 hours was about the limit.

Practically speaking, that is probably close enough,
considering the negative effects of complete discharge.

As you mentioned, discharging the battery 70% in 5 hours
leads one to believe that we are looking at 14% discharge
per hour, or a total run time of about 7.1 hours before
the battery is totally flat.

(70% discharge / 5 hours = 14% hourly discharge rate)
and 1 / 14% = 7.14 hours total run time)

Your CPAP unit appears to be drawing about 3.36 A because:
24 AH / 7.14 hours = 3.36 A or about 41 W

Looked at another way, 3.36 A * 7.14 H = 24 AH

That is not *quite* as high as 5 A.

--Winston

 

[W. eWatson]

On 2/24/2012 2:48 PM, Winston wrote:

W. eWatson wrote:

(...)

I think my Fluke meter measures amps. I don't have a humidifier. My
one at home experience with the Xantrex and the cpap
suggested pretty convicingly that 5 hours was about the limit.

Practically speaking, that is probably close enough,
considering the negative effects of complete discharge.

As you mentioned, discharging the battery 70% in 5 hours
leads one to believe that we are looking at 14% discharge
per hour, or a total run time of about 7.1 hours before
the battery is totally flat.

(70% discharge / 5 hours = 14% hourly discharge rate)
and 1 / 14% = 7.14 hours total run time)

Your CPAP unit appears to be drawing about 3.36 A because:
24 AH / 7.14 hours = 3.36 A or about 41 W

Looked at another way, 3.36 A * 7.14 H = 24 AH

That is not *quite* as high as 5 A.

--Winston
Be aware that my memory may not be accurate on that matter. I did the

experiment about 6 weeks ago.

 

[Winston]

W. eWatson wrote:

On 2/24/2012 2:48 PM, Winston wrote:

(...)

That is not *quite* as high as 5 A.

--Winston
Be aware that my memory may not be accurate on that matter. I did the experiment about 6 weeks ago.

Your ammeter measurement will show the real info.

If your battery is new, it could be more than 24 AH.
And if it has some hours on it, it could be less than
24 AH of capacity. This would affect my guess pessimistically/
optimistically, respectively.

--Winston