Hi amts, and you are correct in that DC/DC devices charge at a lower current than an alternator can, but they also charge at a MUCH lower voltage than an alternator can.
Because of all the glossy but deliberately misleading advertising surrounding DC/DC devices, most people think because the adverts say a DC/DC device charges at a higher voltage, that this is the case for the whole charge cycle.
The reality is that this misunderstanding could not be further from the facts.
DC/DC devices ( and battery chargers ) are only able to charge a given battery at their highest voltage level when the battery is near fully charged, say from around 80% SoC or higher. And this depends on the size of the battery and the current rating of the charging device.
When charging a low battery, for the major part of the charge cycle, both DC/DC devices and battery chargers ( solar regulators ), charge at a much lower voltage than what the average LOW VOLTAGE operating alternator will charge at.
This is something that is very simple to demonstrate, even if you do not have a DC/DC device.
DC/DC devices are just battery chargers with an inverting input stage, but otherwise their output acts similar to that of a battery charger.
To this end, if you have a battery charger, next time you have a battery in a low state of charge and you are going to use the charger to charge it, first measure the voltage at the battery’s terminals before you connect the charger.
Then with the charger connected and turned on, measure the voltage at the battery’s terminals when the charger indicates it is in the BULK mode.
You need to make sure the charger is in BULK mode because some battery chargers analyse the battery’s SoC before they actually state charging the battery.
While a charger is analysing the battery, the terminal voltage will most likely be no higher than your first voltage measurement.
Once the battery charger is in BULK mode you can see voltages as little as half a volt higher than the battery’s original low voltage level.
As the battery charges, the terminal voltage will rise and eventually, the terminal voltage will reach the battery charger’s selected maximum charging voltage. This will only occur in the final stage of the charge cycle.
NOTE, this is a total contradiction of what most people think happens and what the DC/DC device sellers don’t want you to know.
It just does not look so good for their products when you know exactly how they REALLY work.
Because of all the glossy but deliberately misleading advertising surrounding DC/DC devices, most people think because the adverts say a DC/DC device charges at a higher voltage, that this is the case for the whole charge cycle.
The reality is that this misunderstanding could not be further from the facts.
DC/DC devices ( and battery chargers ) are only able to charge a given battery at their highest voltage level when the battery is near fully charged, say from around 80% SoC or higher. And this depends on the size of the battery and the current rating of the charging device.
When charging a low battery, for the major part of the charge cycle, both DC/DC devices and battery chargers ( solar regulators ), charge at a much lower voltage than what the average LOW VOLTAGE operating alternator will charge at.
This is something that is very simple to demonstrate, even if you do not have a DC/DC device.
DC/DC devices are just battery chargers with an inverting input stage, but otherwise their output acts similar to that of a battery charger.
To this end, if you have a battery charger, next time you have a battery in a low state of charge and you are going to use the charger to charge it, first measure the voltage at the battery’s terminals before you connect the charger.
Then with the charger connected and turned on, measure the voltage at the battery’s terminals when the charger indicates it is in the BULK mode.
You need to make sure the charger is in BULK mode because some battery chargers analyse the battery’s SoC before they actually state charging the battery.
While a charger is analysing the battery, the terminal voltage will most likely be no higher than your first voltage measurement.
Once the battery charger is in BULK mode you can see voltages as little as half a volt higher than the battery’s original low voltage level.
As the battery charges, the terminal voltage will rise and eventually, the terminal voltage will reach the battery charger’s selected maximum charging voltage. This will only occur in the final stage of the charge cycle.
NOTE, this is a total contradiction of what most people think happens and what the DC/DC device sellers don’t want you to know.
It just does not look so good for their products when you know exactly how they REALLY work.
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