Date: Mon, 6 Aug 2007 06:43:02 -0400
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: T3 Westy's; batteries; how to have your cake and eat it
In-Reply-To: <e3e1d7f0708052009h31c697f9r80854761f7026abb@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
The sure power is just one brand, example of battery combiners. You're
right, the 12.8 volt cut off is too high to use the combination as an
additional source. There are other out there and most have lower cut offs
and some are adjustable. My last and present motor home, (National RV),
use a custom solution with there own control board. Cut in is about 13.2
volts, (ensures charging). But once connected, will not drop out until
11.8 volts. There is a battery boost switch, (momentary) on the dash. It
is occasionally used to get the generator started if the house batteries
are too low as it is wired to them.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Martin Jagersand
Sent: Sunday, August 05, 2007 11:10 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: T3 Westy's; batteries; how to have your cake and eat it
The sure power's are also voltage triggered relays, but specs say they
cut out at 12.8V. (www.*sure**power*.com), unless you manage to somehow
adjust the voltage breakpoint (this option was not mentioned on the web
site).
No load, full charge voltage of a 12V lead-acid is 12.6-12.7V. A
12.8Vcut-off
voltage means you won't effectively draw camping power from both
batteries.
ie two 70Ah batteries isolated with a surepower gives 70Ah for camping,
while
two isolated with an isolator with a relay with a 12V breakpoint gives
100+
Ah
Useful voltage breakpoints for two 12V deep cycle batteries in parallel
are probably in the range from 12 - 12.4V. With a 12V relay, one can raise
the cutoffpoint to 12.2 V by putting a shottky diode in forward series
with
the
sense wire; 12.4 V with two etc, but it is not so trivial to lower the
cutoffpoint
point witout access to the internal circutry, unless this has been
explictly
provided for in the design.
The "battery protector" I got will always charge both batteries in
parallel,
while the sure power will start the bulk charge of one first, then the
other.
The former is quicker if one has a powerful alternator, while
the latter is maybe a bit milder on the alternator. I've had old 65A
alternators cut out on the older vans due to overload. I don't
have any problem with my 120A alternator even with the 3 battery setup I
put in the '94 Westy.
At the $27 Canadian tire sale price I thought I got a good deal.
Hopefully quality is at least decent. CT puts their own labels on
a lot of OEM stuff. Some is good quality, some not. So far I have
had good luck with the electrical stuff. (e.g. most of their inverters
are actually relabeled Xantrex, a well known brand.)
Martin
On 8/5/07, Dennis Haynes <d23haynes57@hotmail.com> wrote:
>
> You went through a lot of trouble to basically do what a battery
combiner
> or smart relay such as the sure power 1315 does. The sure power uses a
> wide range so that after cut out at 12 volts, it will not cut back in
> until one of the banks gets up to 13 volts which would indicate a charge
> source is now there. This set up arks great even with a conventional
> strting battery combined with deep cycles.
>
> Dennis
>
--
Martin Jagersand
University of Alberta
http://www.cs.ualberta.ca/~jag/
