Thread: DC-DC charger- which one?

Originally Posted by drivesafe

Remove the control off the alternator and the ECU ( BMS ) will have a hissy fit.

dont need to remove it, just make it do nothing, but make it think its doing what it wants.

bit hard for me to talk when i've not seen the system.

Originally Posted by Eevo

bit hard for me to talk when i've not seen the system.

never seems to stop you....

Originally Posted by incisor

never seems to stop you....

Originally Posted by Blknight.aus

Just one point.

Not all Dcdc chargers are constant current a fair number of them attempt to replicate the output of an alternator and aim for a fixed volt?ge. With a varying amps rate once they are able to achieve that voltage.


For the purpose of this discussion the discrepancy is almost moot but for the fact that they won't overcharge a battery for the same reason an alternator won't and if your trying to diagnose them and are tracing the amps flow they behave slightly differently

Proper multi-stage DC-DC converters charge at a constant current (bulk charge) until the drain from the subject battery drops to a certain level then they charge at a constant voltage (Absorb mode) for a fixed time, after which they drop to a lower constant voltage in float mode.
The constant current rating of the charger should be selected to match the maximum safe charging rate of the house battery, and the fixed voltage stages (absorb and float) are selected to suit the battery chemistry.
This charges the battery completely and safely. When charging from an alternator it is not possible to drop into float mode when the house battery is fully charged, so life of the house battery is reduced due to over charging. Similarly, the alternator has no way of knowing the safe maximum charge rate of the house battery so it can easily overcharge it in both modes.
That is why DC-DC chargers were invented........

When charging from an alternator it is not possible to drop into float mode when the house battery is fully charged, so life of the house battery is reduced due to over charging. Similarly, the alternator has no way of knowing the safe maximum charge rate of the house battery so it can easily overcharge it in both modes.
That is why DC-DC chargers were invented........

a reminder to all that may reply, that this discussion needs to remain "educational"

not "confrontational"

Originally Posted by incisor

a reminder to all that may reply, that this discussion needs to remain "educational"

not "confrontational"

factual and accurate too please

Originally Posted by Silenceisgolden

house battery,

whats the difference between a house battery and car battery?

Hi Silenceisgolden and sorry mate but that is straight out of the advertising B/S they use to try to convince people that an alternator can't charge batteries but these wonder devices can.

First and foremost, the charging algorithms of DC/DC devices are a copy of how battery chargers operate.

As such, battery chargers can be connected and charging batteries for many months at a time.

This is why they have a float mode. If you kept a constant voltage of 14.4v on a battery, after about 24 hours, you would start to DRY the battery out.

So to avoid DRYING OUT the battery, these devices MUST lower the voltage being applied to the battery.

If you apply a constant voltage of 14.7 or higher, you will end up cooking a battery. Again, to avoid cooking batteries, chargers do not stay at such high voltages for very long. ( time depends on the chargers make and model )

Now as DC/DC devices use the same style of electronics as battery chargers, its just simpler to use the same algorithms.

It is as simple as that.

As for alternators shortening the operating life spans of batteries, there is not only no evidence to back that advertising crap, but reality and 60 to 70 years of RV use clearly demonstrates the exact opposite is the case. Just more misleading advertising hype, used to try to convince people they need something that will achieve nothing over what an alternator can do.

Now some real facts. How many times have you heard of an alternator cooking batteries, can't happen, but you hear of plenty of cases where DC/DC devices have cooked batteries.

How many vehicle manufacturers advise not to have a fridge powered from any battery being charged from the vehicles alternator?

There are a number of brands of DC/DC devices that state exactly that. You must not power a fridge from any battery being charged by their DC/DC device, because the fridge cycling on and off can cause many DC/DC devices to overcharge the battery.

Then there is the problem of mixing battery types. Not recommended when using a DC/DC device.

Yet when using an alternator, not only can you have any number of mixed battery types but they will each be charged at the optimum charge rate for each battery, regardless of type or state of charge. Can't do that with a DC/DC device ( or battery charger ).

With all the wonder devices on the market today, alternators are still the ultimate and safest way to charge any type of lead acid battery.

I could go on but most of you will get the CORRECT picture.