Phil,
High amp solenoid relays were not that reliable for many years unless they
were very expensive. I would have to think that reliability and cost are
probably among the major reasons that these battery combiners have not been
more popular in the RV industry. A diode isolator has no mechanical parts
and should last forever if operated below its rated capabilities. A
battery combiner (of the relay type at least) has mechanical parts which
are probably more likely to fail. They are also often rated for lower
currents than the isolators. We have a high amp alternator which can put
out more amps than the continuous rating of the battery combiner mentioned
here. A cheap isolator, on the other hand, is rated for the high amps and
has worked for several years with no problems.
Another thought is the idea of 12V batteries in parallel. That seems to be
basically what the battery combiner does. It is only when a charge is
being applied, but if one battery dies suddenly, the other would probably
be affected as well. The isolator seems to keep the two banks more
separated, so maybe it would not be such a problem. Anyone have any
thoughts on this?
Current draw might be another consideration. If solenoid relays are used,
there would be some current draw. The very small (30-40 amp rated though)
automotive type relays we have used draw at least 1 mA. Assuming that a
solenoid like the one used in the GMC battery booster switch is used in
these battery combiners, I would think that the current draw would be quite
a bit higher (.1 A or so). The stats listed below indicate a current draw
of only .1 mA though. Do they use something other than a solenoid relay to
connect the batteries, or should it have been .1 A. Even .1 A would be
better than the voltage drop the isolator causes though, so this idea is
probably not very valid.
Overall, IMO cost is probably the biggest factor. Looking at all the high
dollar stuff in the West Marine catalog and stores, I think that average
boaters might spend even more on their boats than average RVers spend on
their RVs (yes even GMCers
. This may help explain the difference in
popularity of the more expensive battery combiner when RVers and boaters
are compared. For an example, just take a look at which catalog has the
$400 Statpower converter/charger. West Marine carries it, and ,IIRC, even
has a version with their name on it. I assume that they have carried this
type of converter/charger for many years, while the RV industry seems to be
switching over only recently. Most of the RV catalogs still only offer old
style convertors or possibly cheap new style ones. I don't expect a
"Camping World" version of any $400 convertor/chargers any time soon
.
Each market carries what they think they can sell. This is why we have to
look around at many different stores/markets if we want to find the best
products for our GMCs. We always look through all our racing, industrial
supply, marine, RV, etc catalogs when we are looking for upgrade parts for
our GMC so that we know all the options available.
Zak
>Eugene,
>
>I often wondered why the RV industry never embraced the battery
>combiners over the diode isolators because as you point out there appear
>to be several factors in their favor:
>> The features are:
>>
>> 1 No one half volt drop in the charging voltages-- allows full
>> charge.
>> 2 Automatically senses the charger, shore power or alternator
>>
>> 3 Disconnects when the chargers stop
>> 4 Only draws .1 ma when the chargers are in operation
>> 5 Maintains both batteries charge.
>
>The marine industry uses the combiners I believe because major suppliers
>like West Marine sell several models and extoll their virtues. So,
>can anyone share what the disadvantages of combiners are when compared
>to the stock diode isolators we have in our GMCs?
>
>Phil Stewart
>'76 Transmode, TN
>
