GBM wrote:
"Jeff" wrote in

I have read that the current to the
starting battery should be limited by the wire gauge used.

Dangerous thinking there - small wires limit current with a voltage
drop. The reduced voltage may prevent the battery from overcharging
but the wires will be heating up! Also, it means that what the
regulator thinks is a trickle charge will be no charge at all at the
end of the voltage drop.


I think I read that oversizing the connections can cause problems such

as too high a

current flow through the combiner. In the case of the Echo-Charge, how

does

it "control" the current flow? Is it just a resistor?

Perhaps someone with a deeper understanding of electronics will
correct me, but I've never heard that "oversized" wires cause a
problem by passing too much current. On the contrary, the voltage
drop can really mess up any attempt to regulate the charge voltage.


Jeff - I read about this in this link:
http://www.yandina.com/acrobats/C150Data.pdf
that was posted here by Andina Marie Foster. This is what is says:

3. Connect one high current terminal to the positive terminal of each
battery bank.
Secure the ring terminals tightly under the flat washer and lock washer
supplied on each Combiner 150 power terminal. A 7/16" socket wrench will be
required to access these connections in the insulated cavities. No other
cables should be on these terminals at the combiner end.
IMPORTANT:- Use only 6 gauge cable. Use a minimum of 6 feet of wire total
between the positive battery terminals to connect the combiner.
DO NOT use a heavier gauge (lower gauge #) wire. Do not coil excess wire
which can confine heating or
create magnetic fields and upset your compass. The insignificant resistance
in these leads will result in no voltage
loss at end of charge but it is enough to protect the Combiner 150 from
excessive currents which can flow when
the batteries are first connected in parallel.


OK. But what's really going on here is that the normal high current
path is from the alternator (or large charger) directly to the large
house bank. It would be foolish to use 6 gauge for this because when
passing 100 Amps the Voltage drop could be 10% (check out the chart in
the West Catalog). This can have a HUGE affect on the charging if
14.4 Volts is dropped to 13! (People don't always consider that if
the alternator is 12 feet from the battery, the run is 24 feet, and
even 1 gauge will have 3% drop, or 0.4 Volts, enough to greatly affect
performance.)

The wire they are talking about is tapping off that to feed the
combiner which feeds the starting battery. For the primary purpose of
keeping that battery charged, the current flow is probably under 15
Amps so there is no issue at all with Voltage drops. In the rare case
where the charging current is high enough to cause a drop, the
situation would resolve itself fairly quickly. Thus, they can use
smaller relays with the reduced current.

However, if you want to use the house bank for starting the engine (by
forcing the combiner) then you're getting back into a high current
range where the will be a drop, something you might not want in this
situation! Consider that your house bank could be down to 12 Volts,
then you find your starting battery is dead. Forcing the combiner
seems like the right thing, but the starter load (plus the load of the
dead battery) means that the current in the 6 gauge forces a 10%
voltage drop, and now you trying to start the engine with under 11
Volts! This is why I have shutoff switches on each battery and can
quickly rewire any battery to either starter.



And also from Yandina site:

Q Is the 6 gauge wire recommended for the 150 amp combiner heavy enough?
A Yes, in fact this is a MAXIMUM size, using a heavier gauge can damage
the combiner. Increasing the length above the minimum recommended can
actually prolong the contact life with virtually no reduction in charging
efficiency. See the following question for more information.

Q I installed a 50 amp combiner on my boat which has a 90 amp alternator.
Last year the contacts welded shut so I replaced it but now it has happened
again. Should I have used a 150 amp combiner?
A No, the 50 amp combiner is probably adequate. Typically only a portion
of the current flows through the combiner because the charging source is
connected directly to one of the banks. Your problem is most likely that the
installer did too good a job and did not follow the installation
instructions. The intuition that bigger is better applies to most
installations, however it can kill a combiner. The instructions for the 150
amp combiner recommend a minimum wire run from the battery of 3 feet to each
combiner terminal and recommend a wire size no heavier than 6 gauge. The
leads come already attached with the 50 and 100 amp combiner which must not
be shortened. This wire has a negligible resistance to the normal charging
current and has zero voltage drop as the batteries reach full charge but it
does have enough resistance and inductance to prevent the contacts welding
when the batteries being combined are at different voltages and one battery
is supplying high power to the other for a few seconds.

This doesn't make me happy. Or perhaps I should say I feel justified
in switching to the EchoCharge. It also might explain why I've seen
a few combiners fail when the relay are "certified for millions of
cycles"!



This kind of thing makes me wonder if I am adding yet another item that
might give me trouble!

GBM