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No Diode Voltage Drop Effect!


The Hellroaring battery isolator / combiners BIC-95150B and BIC-95300B 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 operating times.   

Now the Good News!

When using the Hellroaring BIC-95150B or BIC-95300B, the voltage drop is expected to be less than 0.005V at full charge (Our test vehicle measured about 0.001 Volt across a an original 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! This drop is even less with the BIC-95xxxB models because their ON resistance is less than half of the original model.


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:

  1. You must remember to disconnect!  It doesn't work if you don't disconnect.

  2. Some connections are frustratingly difficult to remove.

  3. 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 failure. 

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:

Drawbacks to Diode Isolator

Hellroaring's BIC Solution

1 The alternator 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!
2 Many alternators can not output the higher voltage with remote sensing. Works great with internal sense alternators!
3 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. No alternator modifications mean normal output and normal life expectancy.
4 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.
5 Large heatsink limits appropriate mounting spaces. Smaller size enables more choices!
6 Should you desire to supply current from both batteries at once, you must add other high current switching devices. Built-in capability to manually switch both batteries to share the current to the main circuit loads.    This can include starting current or winching current.


Contact Information

For General Information, Sales, Technical or Customer Support:

Telephone: 406-883-3801
Postal address: P.O. Box 1521, Polson, MT 59860
Electronic mail: sales23@hellroaring.com
Sales/Pricing info: Sales page

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Last modified: 10-31-2023