At 07:38 PM 7/1/2009, Eric Thompson wrote:
Ben Okopnik wrote
<snip>
However, since that long-wire resistor would now be
in series with the "second" battery
<snip>
I guess you forgot about the charge/use switch?
The long wire is only in series when charging. When the switch is in the
'use' position there is no difference between the wiring of the first and
second batteries.
Eric Thompson
Yes, it seems this discussion grew into somewhat of a monster.
To reiterate, Phillip has a Pur 35 watermaker with a 24V motor. This
unit draws 2.25 to 2.5 AMPS at 24V. He wrote the watermaker is about
15 ft. from his house bank. A 30 foot run (15 there and 15 back)
calls for a recommended wire size of #18. At that current draw, a
small utility batter, also available in a deep cycle for small
trolling motors, will run the watermaker for about 10 hrs. More than
enough since they're usually run 4 or 5 hours a day. A group 24
battery would run it for about 40 hours. It doesn't matter when in
series that the AMP Hour rating is lower than the house bank - the
extra battery will just discharge more than the house bank..
My suggestion was to use a DPDT 30 to 50 AMP switch to select series
or parallel for charging, or a DPDT relay, available for up to 600
AMPS, but EXPEN$IVE. A #10 wire with the short run needed, I figured
on 8 ft, 4 there and 4 back, is rated for 60 AMPS. Now there's really
not going to be any more current than that for charging, mainly
because of the internal resistance of the smaller battery. I don't
see Phillip running the "extra" battery dead. I use either a group 24
or deep cycle utility battery for the trolling motor on my dinghy. I
usually charge them by paralleling with the house bank with a
"cigarette lighter" plug with about 4 ft of #14 wire. There's a 10
AMP fuse in the plug and it's never blown. Checking with an ammeter,
it usually shows 5 to 7 AMPS, 8 AMPS max. Oh yes, the wire has never
felt warm, much less hot.
Remember guys and gals, KISS!!!
Here's something I wrote to the list back in 2001. I was reminded of
it with all the wire/charging discussion:
================================================================================
We want to design and build a boat hook. First step is to define the beast.
We need to reach a piling or something, so it's an extension of our arm. A
few measurements show it needs to be about 8-ft long. We're going to pick up
lines, pull the boat in and push it out. So we need something on the end to
hook or grab and something we can place against a surface and push.
I'm going to skip the part about all the beam calculations and moment arms
and stuff and just say we arrive at the way most boat hooks are made. A
pretty simple real world device.
Now comes the quagmire. We know it will take a certain amount of effort to
hold the thing out while reaching. If we could lighten it, even by a small
amount, that effort would be reduced. Instead of 1" tubing, we can go to
1/4" tubing to reduce weight. This is fine for pulling, but will not hold up
to the average human force for pushing. We need 3 cables and spreaders.
1/16" Stainless cable is too heavy, so we're going to use 1/64" carbon fiber
cables and spreaders.
Of course we now have a storage problem so we have to figure a mechanism to
allow the spreaders to fold down and some way to shorten the overall length.
More work and we come up with light titanium hinges and tiny teflon pulleys
at the end of the spreaders.
Eight months and $3,800 later, we have a high tech boat hook that mostly
works. We've been able to cut down operator effort by a whopping 2.24123%!!
A plus is the thing is 3.3265% lighter, so we can carry another tablespoon
of fresh water aboard without adding to our displacement!
Or we could just grab an old U-bolt out of the junkbox and lash it to the
end of a 2 X 2. Definitely ugly, very likely embarrassing to use in front of
others, but in the real world pretty doggone close to as good as a standard,
off the shelf boat hook.
This does bring up a question. How much would boat hooks have to cost for
you to use this junkbox special? $100? $500? $1,000? Personally I'd grumble,
but go for $100. Any more and I'd have a couple 2 X 2's lashed to the
lifelines!
Another question. Is the added efficiency of the "high tech" boat hook worth
the extra cost?
================================================================================
Rick Morel
S/V Valkyrie
lying Slidell, LA
Rick 'n' Cathy
S/V Valkyrie
http://www.morelr.com/valkyrie
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