Installing a DC-DC Battery Charger

bernieproberts wrote:I have now swapped the AGM battery for an EFB battery. Thanks for pointing out the charging voltage required for the AGM battery. Taking the motorhome for a run with the old discharged battery the voltmeter reading across the battery read 13.8+ volts. I am happy now I know the Sargent system is working correctly.

It was interesting that no one reported that they had a DC-DC Battery Charger fitted to their Motorhome. I will look into the advantage of installing the Schaudt WA121525 but it looks a little tricky to install whereas the B2B is a straight Starter to Habitation battery connection.

Glad you have swapped it for an EFB battery, they are tolerant of low charging.

There is little that is easier to install than an Schaudt Intelligent Alternator booster. 

A B2B has twin chunky cables running from the Starter battery to the B2B. Then two cables go from the B2B to the habitation battery.
Depending on where the 'cable runs can go' and the distance between the Starter battery and the Habitation battery, that can be fraught.

Depending on the Motorhome Power Controller installed, the 'direct battery to battery' can bypass some functionality 

The Schaudt Intelligent Alternator Booster sits in the existing cable from the Starter battery to the Sargent ECxxx. All that is required is for the Starter battery feed into the Sargent to be cut and the Schaudt unit to be installed in the break in the cable. The 'Cut' end that comes from the Starter battery goes into the Schaudt 'input' and the Boosted Alternator output from the Schaudt connects to the other cut end that goes into the Sargent.

It is literally that simple, a quarter of the time to fit than a B2B. You can connect up temperature sensors and voltage sensors that make the unit even more efficient, if you wish.


The Schaudt Intelligent Alternator Booster takes whatever is being fed to it by the Alternator/Starter battery and turns it into the ideal charge voltage for the batteries, in most cases 14.4v.
As was noted above by the Wildax owner, he achieved 14.41v.  Your 13.8v is still only a slow 'trickle' charge voltage.





A B2B might appear to be 'working', just as 'Fat' cables on their own can, but that doesn't mean you are harvesting maximum power or getting the longest battery life.


Time and again we come across a CTEK 250 B2B installation, which only has a 20amp (peak output, 18amp continuous), so how can that charge multiple batteries at a decent rate?
Charging 3 X 110Ah will put a woeful 6 amps into each battery. 
 That clearly isn't even as good as fat cables and a Big 200amp Split charge relay which can deliver nearly 15 amps per battery.

One CTEK 250 install that was 'still slow to charge' came to us to check it had been installed correctly. The actual installation was done well, using 16mm cables.
We measured the charge which was less that 9amps into each of the two 100Ah batteries, the physical limit of the B2B.

We removed the CTEK which had become the 'limiting factor' and fitted an ordinary 200Amp Relay. The charge went up to just under 15amps per battery.
Like we said above the cables make the biggest contribution.


It is funny how people swear by the installation, yet when you ask what voltage it charges at and the current it puts into each battery, it sometimes goes strangely quiet.

Hi. We have a 2015 MB Burford that has a smart alternator that drops back to 12volts when the start battery reaches a charge of 80%. So the leisure batteries never got charged while driving. I had a Redarc  B2B 25amp charger fitted. This solves the charging issue. It takes the 12v from the alternator and boosts it to 14.6v to charge the leisure batteries. It also isolates the start battery to prevent over charging. It also has a MPPT solar controller.

It works very well and combined with my Votronic Battery Monitor I can see exactly what is happening to my batteries.

Cheers.

naki585 wrote:Hi. We have a 2015 MB Burford that has a smart alternator that drops back to 12volts when the start battery reaches a charge of 80%. So the leisure batteries never got charged while driving. I had a Redarc  B2B 25amp charger fitted. This solves the charging issue. It takes the 12v from the alternator and boosts it to 14.6v to charge the leisure batteries. It also isolates the start battery to prevent over charging. It also has a MPPT solar controller.

It works very well and combined with my Votronic Battery Monitor I can see exactly what is happening to my batteries.

Cheers.

You write -
" boosts it to 14.6v to charge the leisure batteries. It also isolates the start battery to prevent over charging".
That is an odd statement as the Redarcs 14.6v IS overcharging the batteries?   
Almost all wet battery manufacturers give a ideal charge voltage of 14.4v, so clearly 14.6v is going to shorten some Habitation area batteries life significantly.

The Redarc range are strange in having a charge rate that is too high for wet batteries but too low for AGM. If you select the "AGM 14.7v" rate they will be overcharged massively by 15.0v!!!!  
Which brings up another issue.
I think it was the BigRed Campervan website that posted info from Dometic that over 14.5v might be damaging to Dometic Compressor Fridge Electronics and they warned against the use of high voltage chargers, 15.0v is very high. 

The Redarc BCDC1225D is restricted to max 200Ah battery bank according to it's spec. which is low for a B2B, but it's big downside is the 100ma standby current draw. Fine if you use the vehicle every day but it will drop the Starter battery into the sulphation zone in quite a short time if the vehicle stands idle.

You can see how this all supports what we say above how adopting something not specifically designed for motorhomes can have subtle, but devastating, impact. 


You can also see how that just because someone has a B2B installed doesn't make it optimum or workable for everyone. 
When these Redarc units can cost £400, I for one would want the best.