Multiple Battery Banks - One Controller

[VM Systems]

I have seen lots of posts where people are asking about multiple controllers charging one bank, but we are looking at a different option.

One controller but 2 banks.  I have seen a few isolators that are usually used for automotive applications but will work for us.  We have 24V systems and would like a single classic to charge both a "high priority" bank and a "low priority bank".

Samlax makes one that we are looking at to attempt this.

Is anyone doing this?  Feel free to call me crazy

Arthur

[boB]

Hi Arthur...   I have seen this before.  Usually the us an isolator diode but sometimes use a switch to choose the bank.
These aren't all that common but I think RVs and marine are the typical applications.

I've seen an off grid house using two 12V banks but had a controller and PV array for both banks.  If the PV array
is large enough for both banks, then one could just parallel the banks and use one or more controllers to keep it
charged.  Then there are RVs where the starter is on one of the batteries and they don't want to wear down
that battery but might want to run the radio or some other accessories on that battery.

There are evidently AC input battery chargers that will charger 2 or 3 batteries.  I think that Magnum Energy
has or had a 2 or 3 battery charger as well as an active battery bank isolator that takes care of 2 banks
with one charger.  Don't know if those are still being manufactured.

What's your situation ?

boB

[RossW]

Usually the us an isolator diode but sometimes use a switch to choose the bank.
These aren't all that common but I think RVs and marine are the typical applications.

boB

I believe diodes are becoming far less common. That half-a-volt or so drop (even with schottky diodes) represents quite a lot of power to dissipate, and as you'd know, half a volt (or worse) drop will likely stop the secondary battery getting a good charge.

Many seem to be using FETs now. They're quite cheap, and with R(ds) in the milliohms to tens-of-milliohms range, power dissipation is hardly worth mentioning, and voltage drop is getting close to negligible.

[Nomad1]

I'm using this to charge second bank:
http://www.xantrex.com/power-products/power-accessories/auxiliary-battery-charger.aspx

It starts charging when main battery voltage is above 26V and keeps my aux batteries healthy. However, I don't think it could be used for any kind of heavy load since it have max 15A current. Also the device lacks any customization options - there is no way to set min/max voltage, there is no bulk/absorb/float charging modes, etc.

[boB]

Usually the us an isolator diode but sometimes use a switch to choose the bank.
These aren't all that common but I think RVs and marine are the typical applications.

boB

I believe diodes are becoming far less common. That half-a-volt or so drop (even with schottky diodes) represents quite a lot of power to dissipate, and as you'd know, half a volt (or worse) drop will likely stop the secondary battery getting a good charge.

Many seem to be using FETs now. They're quite cheap, and with R(ds) in the milliohms to tens-of-milliohms range, power dissipation is hardly worth mentioning, and voltage drop is getting close to negligible.

Yes, we had a FET diode 20 years ago at Trace Engineering.  I didn't want to confuse the issue.

If he can get one of these, then that's a better way to go.  Just costs more.

boB