The bare, naked, truth and facts about battery charging, split charging and battery monitoring

A 70 Amp split charge diode running at or near rated capacity wastes about 100 watts of precious power by heating itself up. The truth about split charge diodes.

A split charge diode cannot be used without a battery sensing alternator regulator. The charge voltage will be about 1 volt too low if you try. This will reduce the charge current to about 1/10th of what it was before the diode was added. The truth about split charge diodes.

A typical 1 in, 2 out split charge diode will present the engine battery with 0.5 volts more than the domestic battery for a high percentage of the charge cycle. This will either over charge the engine start battery or undercharge the domestic battery. The truth about split charge diodes.

Modern alternators already charge at 14.4 to 14.8 volts. Adding an external alternator controller that forces the alternator to charge at 14.4 to 14.8 volts will therefore achieve absolutely nothing. Alternator controllers.

People that have had problems with relay based split charge systems had those problems because they didn't know how to specify or calculate the correct size relay or cabling. In the same way, putting a 5 amp split charge diode with 5 amp cable onto a 70 amp alternator will end up in failure. The components must be specified and sized correctly for the intended purpose.

Amp hours counter do have their uses. However monitoring the state of charge of batteries is not one of them. For every customer who is happy with their performance as a battery state of charge meter there are probably 10 who know that they don't work for this purpose. I know this for a fact having worked as a technical support engineer for a manufacturer of amp hours counters. SmartGauge compared to amp hours counters.

A split charge diode only splits the charge from the alternator. If a wind turbine, or solar panel, or single output charger is added, yet another split charge system has to be added.

A SmartBank split charge controller uses under 4 Watts when in active split charge mode. A typical split charge diode uses about 100 Watts in the same circumstances.

A typical amp hours counter takes several hours to install. A normal SmartGauge installation takes around 15 minutes.

Installing a split charge diode involves cutting into the factory cables. This can (and actually has) invalidated warranties on vehicles and boats.

Despite an "urban folklore" regarding "14 Mersyside Regional NHS trust ambulances" the reality is that since 2002 several hundred ambulances in the UK alone have been called back into the service depots where the alternator controllers and split charge diodes were removed and replaced with stock alternator regulators and SmartBank split charge systems because the alternator controllers and split charge diodes were not ensuring reliable battery performance.

UV Modular, Wilker and MacNellie (all regular installers of the SmartBank split charge system) are the UK premier ambulance builders accounting for the lion's share of the UK ambulance market. None of them fit split charge diodes or alternator controllers any longer having moved over to relay based systems such as SmartBank. Further, when old ambulances are returned to the factory for updating, they remove any split charge diodes and alternator controllers as a matter of course. This doesn't sit well with the split charge diode suppliers.

Most modern vehicles simply will not allow an alternator controller to be fitted. If one is fitted it either throws up an error in the engine management system or, in the worst cases we have seen, forces the engine management system into "limp home" mode requiring a visit to the main dealer to have the entire engine management system reset (after removal of the alternator controller). This is fact, not fiction.


Page last updated 02/04/2008.
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