Ok, Ian, I now know what you mean by a "combiner" Honestly I thought
that was a UK term for "Isolator pac" or of the sorts.
Ian Malcolm wrote:
Tim wrote:

Ian Malcolm wrote:


Tim, I think you have a small problem . . .

So you've got the Aux battery fed off the engine battery via a diode.

This means that any load on the Aux battery will drain *BOTH* batteries
as if the Aux is lower than the engine current flows through the diode.
*NOT* what you wanted.

If you want to make this work, you'd need to reverse your isolator diode
plate and take the alternator output direct to the Aux battery.



Ian, you are absolutely right, and actually thats what I did. I was
thinking one way and typing another.

And I AM glad you called that to my attention.

And actually, I'm going to revam it some more.

you said, something like : Why don't you use a combiner(Isolater)?"

Actually, I'm going to make my own. A commercially bought isolator
(combiner) is actually

a three(for the most common) post device, which has "Alternator output"
on usually the center post, and "Bat.1" on another, and "Bat 2" on the
third. And this contains a couple heavy diodes to allow the alt to
charge simoaniously both battery banks, yet, leave the bateries
independant of each other. And that's a good idea.

The problem I have with the commercially made products, is that if one
diode diode goes out. Then the whole combiner, as you say, is bad, that
is, unless you wish to press the diode pac out of the finned aluminum
heat sink, and dig through the epoxy, and finally figure out that
you're fairly well wasting your time trying to repair the unit (that
is, unless it's made to be repaired), only to have to go buy another
one.

I have found that it's much easier to have two seperate heat sinks and
configure them to do the same thing as the commercially sold unit.

Reasoning is, that unlike the mounted commercial unit, which you
usually end up having to mount in some hard to get to place (like on a
small power boat), you can take your seperate heat sinks and mount them
anywhere you wish..tuck them in convenient places.

Also, if and when one goes bad, then thats the only one you need to
replace.

besides, I have a bountiful supply of these, just sitting around in the
junk.. LOL!

Thanks for your Input, Ian, I will check out the various threads.

Tim

The three terminal diode devices are definately isolators, but I
wouldn't call that a combiner.

A combiner consists of a heavy duty relay or contactor suitable for
continuous operation that parallels the batteries only when the
alternator is charging the batteries.


Ok, Ian, I now know what you mean by a "combiner" Honestly I thought
that was a UK term for "Isolator pac" or of the sorts.

What you would call a "combiner" is what I call a continous parallel
solonoid.

Commercial products usually sense the alternator output voltage, but
many DIY ones either sense the alternator warning lamp (like mine does)
or run off an oil pressure switch possibly with a disabling relay from
the starter solenoid coil terminals to prevent them engaging while
cranking. The advantage is no diode drops so you dont need to modify
the alternator to boost the output voltage or fit an external battery
sensed regulator to get a full charge on both batteries. It operates
just like a manual battery switch except you never need to remember to
switch it.

http://www.tb-training.co.uk/MarineE09.html#Split%20Charge%20Relay

is worth a look.

If you are interested in fitting something like that, I can dig out
details of the single transistor circuit I used to buffer the signal
from the warning lamp. Its really simple, just a couple of resistors
and diodes (to protect against transients) and the transistor mounted on
a piece of tagstrip or you could just fit a higher wattage warning bulb
as suggested in the link.

Alternatively, since you are in the trade, why not get a caravan or
motor-home split charge relay and beef it up by using its output to
switch a heavy duty relay or contactor (my original plan before I came
accross the discussion on uk.rec.waterways and learned I could save
about £15 by building my own simple controller)


Next year the plan is to extend it with another relay so the fridge and
various chargers for handheld gadgets get switched on automatically
whenever the engine is running and switched off when we are on the hook
unless I override it. Hot bacon sandwiches in the morning and a cold
beer in the evening are glorious to have and both need the fridge to be
run whenever possible . . .

LOL, Yes, I could do that, and that type of system you are describing
works rather well. I have seen it ( or varients of) on commercial
applications. Yes, i could do that, and I am privy to the products, but
in my case, I really do believe that to be quite a bit of overkill for
my purposes. seeing I dont' run a refrigerator, nor a stove.

Hot bacon sandwiches in the morning and a cold
beer in the evening are glorious to have and both need the fridge to be
run whenever possible . . ."

Agreed!


Ian, seeing you are thinking in these lines, if you ever wanted to
increase the power options on your boat and can use your imagination
some.

You can run 12 AND 24 v systems directly off your single 12v alternator
with some not-so-difficult modifications. like, adding a typical Delco
10-SI rectifier, and a transformer (which I cant think of its
electrical values at the moment...but can find out!).

you can have 12v "run, and 24v "options" in one neat little package.

GM has used Delco 30SI units with this modification, in heavy truck and
off-road applications. It eliminates the series/parallel switchs,
relays, and a whole bunch of wires.(not to mention, headaches.)