No Diode Voltage Drop Effect!
The Hellroaring battery isolator / combiners BIC-75150A and
BIC-75300A do not drop significant voltage like a typical
diode isolator does.
Instead, they act more like just a few feet of large gauge
wire when it is switched ON!
When full charge is approached, a diode isolator still
drops from 0.55 to 0.7 Volts. This voltage drop reduces the voltage
available to the battery which inhibits full and complete charging within typical
Now the Good News!
When using the Hellroaring BIC-75150A or BIC-75300A, the
voltage drop is expected to be less than 0.005V at full charge (Our test vehicle measured
about 0.001 Volt across a BIC-75150A. ) This difference is
insignificant to the battery charge! To put this in perspective, there
will usually be more voltage drop in the wires to and from the battery!
Typical Diode Isolator
When you install a second or more batteries either in your vehicle or
towed vehicle, you need a way to prevent discharge of one battery circuit as a result of a
load on the other. For RV trailers, as an example, it is most desired to
prevent a load in the trailer (such as lights, appliances, etc...) from draining your
vehicle starting battery. The least expensive method is simply to disconnect your
trailer plug every time you turn OFF your engine. The drawbacks to this
technique are as follows:
You must remember to disconnect! It doesn't work if you don't
Some connections are frustratingly difficult to remove.
You must remember to reconnect when on your way again!
If the spare battery is in your vehicle, the choice of disconnecting
and reconnecting is even less desirable. To make the isolation more automatic, some
people will place a diode in series with the alternator and main battery. The
drawback of this technique is:
A voltage drop, inherent in the diodes, reduces the charge voltage
to the battery causing the charge current to be significantly reduced. As a
result full charge will not be achieved unless you operate the vehicle for very long
periods. Often, the vehicle is not operated long enough and then, the battery
sits for a while with less than full charge. This condition causes the battery
plates to sulfate, which will gradually degrade its performance and lead to early
To overcome this problem, a second diode is placed in series with the
auxiliary battery and the alternator output is modified to output a higher voltage.
The drawbacks to this technique are:
to Diode Isolator
output must be modified in some way. The particular way is unique to your model
(external sense, tweak regulator voltage, etc...)
||By combining the
batteries during charge, alternator voltage modification is NOT necessary!
||Many alternators can
not output the higher voltage with remote sensing.
||Works great with
internal sense alternators!
||All other conditions
being equal, the higher voltage output in the alternator will cause more heat buildup
resulting in a shorter life and probably less output current capability.
modifications mean normal output and normal life expectancy.
||The total alternator
output current must go through one of the diodes. This requires a large
heatsink to dissipate the heat and a rating for the total alternator output.
||By combining the
auxiliary battery during charge, only the current required for the auxiliary circuit
passes through the isolator. This fact, plus the use of more efficient electronic
devices, results in less heat buildup and a smaller physical size can be used.
limits appropriate mounting spaces.
||Smaller size enables
||Should you desire to
supply current from both batteries at once, you must add other high current switching
to manually switch both batteries to share the current to the main circuit loads.
This can include starting current or winching current.