checking that a blocking diode still works

[saab96]

I have a Sure Power model 2703 blocking diode/battery isolator for an alternator of 70amps, negative ground, terminal connectors 1,1A, 2, 2A, 3. Does anyone know how I can check it still works? Alternatively, how do I check for sure that it isn't working!!

 

[VicS]

This is a 2 input (A1 and A2), 3 output (B1, B2 and B3) device ?

Using the diode test range on a digital multimeter, with all wiring disconnected from the device.


Test between input 1 and out put 1 then reverse the meter leads and check again . In one direction you should get no reading in the other a reading of about 700 which is the forward volts drop in mV

Now move on to test between input 1 and outputs 2 and then 3


Then go to input 2 and repeat all over

In each case you should see the same difference when you reverse the MM leads. No reading one way around the 700 mV reading the other.

It would be a good idea to check your MM instructions! .. they vary a bit


It might work using one of the Ohms ranges if you dont have a diode test range ... meters differ in this respect and as to which range(s) will work. The reading won't mean much but one way you should see infinite resistance but get some reading the other way

 

[saab96]

That should do it!

It sounds like you have done this yourself. Thanks

This is a 2 input (A1 and A2), 3 output (B1, B2 and B3) device ?

Using the diode test range on a digital multimeter, with all wiring disconnected from the device.


Test between input 1 and out put 1 then reverse the meter leads and check again . In one direction you should get no reading in the other a reading of about 700 which is the forward volts drop in mV

Now move on to test between input 1 and outputs 2 and then 3


Then go to input 2 and repeat all over

In each case you should see the same difference when you reverse the MM leads. No reading one way around the 700 mV reading the other.

It would be a good idea to check your MM instructions! .. they vary a bit


It might work using one of the Ohms ranges if you dont have a diode test range ... meters differ in this respect and as to which range(s) will work. The reading won't mean much but one way you should see infinite resistance but get some reading the other way

 

[William_H]

An alternative way is to use a voltmeter to check both battery voltages when the alternator is charging. A rise to about 13.5 volts at the battery terminals should indicate diodes are conducting. With engine stopped put a large load on the house batteries and observe the volt drop. Now observe the voltage of the engine start battery this should not drop with the large load on the house batteries. Next observe the voltage of the house battery (no load) when the engine is cranked over this should not drop with cranking.
That should prove that the diodes are OK for one set of diodes. I do not know why you would have 2 sets however they may simply be paralleled to increse current capbility.
In which case disconnect one input and the associated outputs. To check the remaining input diodes. Reconnect and disconnect the first set tested.
If your system has 3 batteries from 3 outputs then check voltage of all batteries under charge. Should be similar. Then check the isolation of each battery by checking its voltage when another is loaded.
OP may have doubts about battery charging becuase of the volt drop of silicon diodes. The diodes may be working as expected but the inherent volt drop is causing batteries to not be fully charged. The way to deal with this volt drop is to use battery sensing of hte alternator regulator or get a zero volt drop diode device or use a voltage sensing relay.
If the input voltage to the diodes from the alternator is something like 14v when on charge and the battery voltage when the batteries are thought to be charged is around 13.3v
then the volt drop of the didoe is causinmg a problem. If there is no voltage difference between input an output it is either a zero volt drop diode set or a bad didoe. If the voltage at the input is 14.7 or so and the output is 14v then it is using battery sensig as it should or the regulator has a higher voltage to compensate for diode drop.
good luck olewill
good luck olewill
good luck olewill