Thread: Do I need a BCDC charger?

Hmmm, couple of interesting snippets in that - I will not comment however, Drivesafe has summed it up well.

Hi Neil, and sorry mate, I was going to leave commenting on your post, but others will be reading your post and may think this is the best setup.

Originally Posted by Nmritchie

i have heeded the recommendations of people like Colyn Rivers in that DC DC chargers do optimise the charging of each battery.

First off, not a good choice for sourcing advice.

Originally Posted by Nmritchie

I have solar panels on both camper trailer and car and needed MPPT solar controllers for both the camper and car auxiliary batteries, so it was a straightforward choice to put combined DCDC/MPPT units on both.

Because your alternator can charge your batteries quicker than any DC/DC device, you would have saved a lot of money and been able to fit separate MPPT solar regulators to both panel setups.


By having separate solar regs, if your solar panels are setup to be able to charge while you are driving, you could then be recharging your batteries from two sources while driving, meaning much faster recharging, in a shorter drive time.


With your setup, you can only get power from one or the other source, and your charging current is very limited, meaning you have to drive a lot longer to recharge your batteries.

Originally Posted by Nmritchie

I am very happy with the setup, and confident that my crank battery is never being discharged to feed the other batteries, particularly when the engine is not running. If the DC DC charger is sized correctly, it will usually deliver plenty of charge and will never exceed the recommended charging rate. The limit on charge rate is about the only operational criticism leveled at DC DC UNITS.

This limit is a lot worse than you think and depending on how much battery capacity you need to replace while driving, could actually be a big deficits to your batteries.


As for your “cranking battery never being discharged to feed the other batteries, particularly when the engine is not running” This type of operation, which is how my isolators work, allowing the cranking battery to be used to help supply accessories power while the motor if off, has a huge number of benefits over the limited operation of your DC/DC devices.


The major benefits of sharing the load is that none of the batteries would be discharged as low as you have to discharge your batteries in your setup for the same amount of power used, the load is spread over more batteries, so will mean the load is gentler on each battery than what it is in your setup.


Because the batteries are not discharged as low as yours need to be, the recharge time is much shorter than your DC/DC devices can do it in, again, this is a big benefit to battery longevity.


And there is a lot more, but this should help others to decide which is the best/optimum setup.

This is an interesting read from Century Batteries

https://www.centurybatteries.com.au/...y-charging.pdf

Especially this : "Deep Cycle AGM:- AGM batteries should be charged using a charger with a mode switch for AGM type batteries. It is recommended to use a charger, current limited to 20% or 0.2C of the batteries capacity at a charging voltage of between 14.6 – 14.8V following deep cycle use, or 13.6V – 13.8V for standby use. Charging should be paused if the battery or ambient temperature exceeds 50°C."

An alternator of course does not have an AGM setting nor is its current limited to 20% of the battery's capacity (if we assume that the AGM is say 130 amps - big battery for a d2 rear cargo area) that means the charger should not exceed 26 amps. The D2 alt of course has 140amps (from memory) in output capacity at revs. I haven't looked for a while but I cannot recall seeing my alternator output sitting at 14.8v or close to it.

Likewise an alternator cannot shut off/pause charging if the temp of the battery/ambient gets too hot to be desirable for battery longevity. A good DC to DC charger monitors temp and scales back charging and finally pauses it completely if temp is too high...

Likewise I have read many articles where for good long term (we are talking 10 years) AGM life is conferred by slow charging (and of course not running too low). Many examples on the web, but just a quick google shows this Page not found - Know Your Parts

"You can use your regular battery charger on AGM or gel cell batteries.
False. These batteries like to be charged slow and low. Many AGM/gel cell battery chargers have microprocessors that collect information from the battery and adjust the current and voltage accordingly. Some have different settings for charging flooded, gel and AGM batteries. Overcharging can kill these batteries. Also, alternators are not chargers. Don’t rely on an alternator to do the work of a *charger. If a battery is discharged to the point that it cannot start the vehicle, use a charger as soon as *possible to make sure the battery gets fully charged."

An alternator cannot be described as low and slow if the AGM is run down (but still in the safe zone).

Absorbent Glass Mat (AGM) Battery Information - Battery University :

"As with all gelled and sealed units, AGM batteries are sensitive to overcharging. A charge to 2.40V/cell (and higher) is fine; however, the float charge should be reduced to between 2.25 and 2.30V/cell (summer temperatures may require lower voltages). Automotive charging systems for flooded lead acid often have a fixed float voltage setting of 14.40V (2.40V/cell); a direct replacement with a sealed unit could overcharge the battery on a long drive"

Cheers

Sounds to me like every vehicle in the world with AGM batteries is destroying said batteries unless they have a DC DC charger! Sounds like a good basis for a class action against battery makers for not including warnings about connecting their batteries to car electric systems.!
Items seem to be not fit for purpose!

The above comment was made slightly tongue-in-cheek and should be read as such

Originally Posted by Vern

How much Voltage i think you mean!

Yes, voltage.

An AGM is fit for purpose Don. But you research them an buy them and either comply with the charging requirements or dont...your coin. None can just assume that because a vehicle will charge and maintain to a large extent a stock flooded lead acid battery that it follows that the vehicle will charge and maintain other types of lead based batteries.

I think it's also a question of battery life versus battery life...i am happy to pay for a separate charging system in the vehicle if it provides significantly longer battert life and better capacity during that time.

Cheers

Hi Scott, that info is either very old, or Century must be still making old type AGM batteries.

With the exception of AGMs like Optima, most new standard type AGMs will take charge currents of 35% of the Ah and can be charged with voltages up to 14.7-8v.

But this does not ulcer the fact that if an AGM has a limited charging current, then it is not suitable for under bonnet use, because these same AGMs will not tolerate the heat of an engine bay.

So you need to use the correct battery in the first place and in doing so, again, a DC/DC device will simply choke the battery’s charging capability.

Originally Posted by trout1105

Not bluetooth,they just plug into any cigarrette lighter outlet.

Mine came from Jaycar. I forget the price, but it was cheap.