Date:         Sat, 3 Nov 2007 15:39:36 -0400
Reply-To:     Poppie Jagersand <poppie.jagersand@YAHOO.CA>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Poppie Jagersand <poppie.jagersand@YAHOO.CA>
Subject:      Re: Charging deep cycle batteries with the alternator
In-Reply-To:  <4725FC6A.1010903@gmail.com>
Content-Type: text/plain; charset=iso-8859-1

A cheaper but much clumsier approach to charge a deep cycle battery to 100% while driving or idling: Most of us probably already own a regular 120V battery charger, and many already have an inverter.

To charge first separate starting and deep cycle battery (see posts on battery isolator and battery protector for how to do this. If you are using a diode based battery isolator, you are automatically fine as current won't flow backwards. If a relay type you have to either do it manually (mina has a switch for this), or add an extra relay)

Then plug 120V charger into inverter and charger to deep cycle battery.

The crafty person can likely do a fully automatic setup so batteries are automatically charged correctly regardless of if power is from alternator or shore. I was thinking of mounting my charger permanently in the '82 Westy, but didn't get around to it yet. The '94 Westy (and ironically many of the older bay window westies) already has a charger built in to charge the camping batteries. With the '94 annoyingly only the camping batteries get charged from shore power, but not the starting battery. Not an issue for someone who uses it as a daily driver. But I don;t drive anywhere on a daily basis, so I need to charge the starting battery separately a few times a year.

Note 1: If your battery charger is not one of the automatic new types, it may not have the right charge stages and voltages for a deep cycle. I bought a Canadian tire 12/8/2A automatic switching type charger. (Lists for CAD49 this week). It seems to do a good job of keeping my optima battery happy. (I feel I have more capacity in it after charning with this charger than after just charging it with the alternator, but haven't done any scientific tests.

Note 2: Trying this with weak inverters it may not work. With my 1000W Xantrex it works fine. With a 150W "cupholder" inverter I tried a similar trick (actually charging the battery in a UPS unit), and the inverter broke the second time.
The cupholder unit had some kind of overcurrent protection in it, but it was apparently not foolproof.

Note 3: When buying chargers, the new entirely electronic ones with switched power supplies are the most desirable. If a unit has a 10+A capacity and still is lightweight it's probably the real thing. Anything that is heavy is likely old style chargers with a big copper core transformer inside.

Cheers,
Martin

Michael Elliott <camping.elliott@GMAIL.COM> wrote: We have a largish Trojan 130 amp-hour auxiliary battery under the bench
seat in our Westy, Mellow Yellow, and use solar power when camping to keep
it charged up (see
http://camping.elliott.googlepages.com/aboutoursolarpowerrig for details
if curious).

Our solar charge controller is designed to charge deep cycle batteries to
full capacity, but the engine alternator is not. Starting batteries have
thin lead plates so they can deliver a lot of current quickly, and in
routine usage they don't get very deeply discharged. The alternator is
designed to provide a constant voltage (usually around 13.8V or so) and a
lot of current in order to quickly recharge the starting battery. It's an
effective match.

But the alternator isn't very good for recharging deep cycle batteries
with their thick plates. They are best charged by multistage charges which
take the battery through several steps of voltage and current in order to
wring the best performance and operating life, and they like to be taken
to more than 14 volts to completely remove sulfite deposits from the
plates. The best an alternator can do it take the deep cycle to around 85%
to 90% of full charge.

In Mellow Yellow we would routinely arrive in camp with the battery still
16Ah low (as indicated on the Xantrex Battery Monitor -- that's 12% low
for a 130Ah battery), whereas the solar charge controller, a three-stage
design, takes the battery to 100%, if given enough sunlight and time.

I'd prefer to arrive in camp with a topped-off battery: having an extra
16Ah gives a little extra freedom in not having to deploy the solar panels
so soon, it might allow an extra day of camping in overcast conditions,
and that missing 12% matters more if we're trying to avoid discharging the
battery below, say, 50% to help prolong its life.

So I've been looking for a way to properly charge the deep cycle battery
from the alternator while driving and I think I've found a good solution:
a four-stage DC input charger which operates off the alternator. It's made
-- or distributed -- by Powerstream and the model I'm trying is their
PST-BC1212-15 (http://www.powerstream.com/DC-input-chargers.htm).

It operates at input voltages ranging from 10 to 15VDC, and provides up to
15A peak charging current (switchable to 7.5A) and trimpot adjustable for
custom values (the online specs don't mention 15A peak current option, but
it's there), with trickle, bulk, fill, and float charge functions. It also
has low input voltage protection, high input voltage protection, over
temperature protection, output short circuit protection, and battery
polarity protection. It does everything except get you elected Queen of
the May!

In a brief test with an idling engine (13.7 volts from the alternator) the
charger took the 10% discharged deep-cycle up to 100% in about an hour. It
started by putting in more than 16A @ 14.4 volts, then pulled back the
current as the battery reached full charge and went into float mode. Seems
to work just peachy.

With just the alternator I wouldn't normally bother to try to charge the
battery from the idling engine but with this gadget it's good to know that
I can fully recharge our deep cycle when away from 120VAC, parked in camp
on a rainy day.

I've mounted the charger in the secret space forward of the potable water
tank (the compartment behind the AC outlet and circuit breaker) and will
see how it performs over the course of the next few trips.

--
Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
KG6RCR



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