Seeking Dual Car Battery Installation Advice

[W. Watson]

I'm about to configure my 97 Plymouth van so that it has two batteries. The
second battery will be kept in the rear of the van in a battery box with a
vent through the floor. I'm using a Mega-Tron RV-Marine Deep Cycle 12v
battery, which will provide power to a medical device at night. I bought a
Valmar (Model 31122) battery selector switch. The switch has four settings:
Off, 1, All and 2. I suspect that 1 means batter 1, and 2 battery 2.

I have a pretty fair idea how to install it ignition and ground wise. I know
the difference between +/-, for example. I'm going to need some wire to go
from the rear to front under the chassis. Does #10 seem right? I'll try to
keep it tight and away from the fuel tank. It seems best to put the switch
inside the engine compartment. I think I'll be able to drill a 1" or so hole
through the floor in the rear of the van. Maybe I'll call the Plymouth and
ask for advice on that. Any suggestions or comments on all this?

I plan to put a 30A fuse inline.

 

[Jumpster Jiver]

I'm about to configure my 97 Plymouth van so that it has two batteries. The
second battery will be kept in the rear of the van in a battery box with a
vent through the floor. I'm using a Mega-Tron RV-Marine Deep Cycle 12v
battery, which will provide power to a medical device at night. I bought a
Valmar (Model 31122) battery selector switch. The switch has four settings:
Off, 1, All and 2. I suspect that 1 means batter 1, and 2 battery 2.

I have a pretty fair idea how to install it ignition and ground wise. I
know
the difference between +/-, for example. I'm going to need some wire to go
from the rear to front under the chassis. Does #10 seem right? I'll try to
keep it tight and away from the fuel tank. It seems best to put the switch
inside the engine compartment. I think I'll be able to drill a 1" or so
hole
through the floor in the rear of the van. Maybe I'll call the Plymouth and
ask for advice on that. Any suggestions or comments on all this?

I plan to put a 30A fuse inline.

Your best source for wire, connectors, fuse holders, etc. would be to
maybe buy one of those amplifier installation kits.
Get the heaviest duty one you can get.

 

[Yukio YANO]

I'm about to configure my 97 Plymouth van so that it has two batteries. The
second battery will be kept in the rear of the van in a battery box with a
vent through the floor. I'm using a Mega-Tron RV-Marine Deep Cycle 12v
battery, which will provide power to a medical device at night. I bought a
Valmar (Model 31122) battery selector switch. The switch has four settings:
Off, 1, All and 2. I suspect that 1 means batter 1, and 2 battery 2.



I plan to put a 30A fuse inline.

a 30 Amp fuse seems to be a little on the small size as does the 10
gage wiring.

Check with a RV Shop on wiring size !!! or else use the same gage as the
battery cables already on the car.

the 30 Amp fuse might be suitable for your load but not for the charging
side of the circuit.

I am a little suspicious of a Dual Battery setup without Isolation Diodes.

Usually you would expect to be able to Start the engine using the
auxillary Battery in an emergency, hence the need for heavier cables
than 10 gage.

Yukio YANO

 

[Arfa Daily]

a 30 Amp fuse seems to be a little on the small size as does the 10 gage
wiring.

Check with a RV Shop on wiring size !!! or else use the same gage as the
battery cables already on the car.

the 30 Amp fuse might be suitable for your load but not for the charging
side of the circuit.

I am a little suspicious of a Dual Battery setup without Isolation Diodes.

Usually you would expect to be able to Start the engine using the
auxillary Battery in an emergency, hence the need for heavier cables than
10 gage.

Yukio YANO

I'm no expert on this, but I do know that it's not as simple as just having
two batteries that can be switched between each other. As Yukio says,
there's normally a dual charge control box, which does indeed contain at
least isolation diodes. My next door neighbour went through all this when he
converted a van to an RV for touring round Europe. I think it would be wise
to take professional advice from a reputable auto electrical shop on this
one, or at least post the question on one of the auto repair groups that
might have a genuine expert in this field.

Arfa

Arfa

 

[Meat Plow]

I'm no expert on this, but I do know that it's not as simple as just having
two batteries that can be switched between each other. As Yukio says,
there's normally a dual charge control box, which does indeed contain at
least isolation diodes. My next door neighbour went through all this when he
converted a van to an RV for touring round Europe. I think it would be wise
to take professional advice from a reputable auto electrical shop on this
one, or at least post the question on one of the auto repair groups that
might have a genuine expert in this field.

The batteries also have a different charge rate.
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[PeterD]

I'm about to configure my 97 Plymouth van so that it has two batteries. The
second battery will be kept in the rear of the van in a battery box with a
vent through the floor. I'm using a Mega-Tron RV-Marine Deep Cycle 12v
battery, which will provide power to a medical device at night. I bought a
Valmar (Model 31122) battery selector switch. The switch has four settings:
Off, 1, All and 2. I suspect that 1 means batter 1, and 2 battery 2.

I have a pretty fair idea how to install it ignition and ground wise. I know
the difference between +/-, for example.

Good idea? Humm...

I'm going to need some wire to go
from the rear to front under the chassis. Does #10 seem right?

For what? Charging? Probalby not large enough. I'd suggest 4 AWG (both
positive and negative, don't use the chassies for ground).

I'll try to
keep it tight and away from the fuel tank.

Define 'tight'...

It seems best to put the switch
inside the engine compartment.

If you are not going to use the switch, why bother installing it? You
going to open the hood each time you use the battery? I doubt it. Also
I suspect the switch, and your understanding of how it works, and what
it does, is flawed. You should have a battery management system, not a
simple switch.

BTW, Valmar's web site is dead so I can't look anything up there.

I think I'll be able to drill a 1" or so hole
through the floor in the rear of the van.

OK, but use proper installation practices in running the cables.

Maybe I'll call the Plymouth and
ask for advice on that.

Bwah-ha-ha-ha... They won't know, or care. Don't waste your time.

Any suggestions or comments on all this?

Yes, you are going about it without considering everything. BTW, if
this 'medical' equipment is life support/life critical, I'd recommend
you get professional help.

I plan to put a 30A fuse inline.

For what? That dinky 10 AWG wire? It will blow the first time the
battery needs a complete charge (and the 10 AWG wire would also fail).

 

[neon]

i think i allready told you what to do. one battery for extra equipment tie the anode of a diode 30amp or more to car battery put a switch in series to disconnect car battery from secondary battery close it when driving to charge the secondary battery the battery if totaly discarged can charge at a big rate so the wires must be 12 gauge or less.

 

[Jim Yanik]

I'm no expert on this, but I do know that it's not as simple as just
having two batteries that can be switched between each other. As Yukio
says, there's normally a dual charge control box, which does indeed
contain at least isolation diodes. My next door neighbour went through
all this when he converted a van to an RV for touring round Europe. I
think it would be wise to take professional advice from a reputable
auto electrical shop on this one, or at least post the question on one
of the auto repair groups that might have a genuine expert in this
field.

Arfa

Or check with an RV group.

 

[James Sweet]

I'm no expert on this, but I do know that it's not as simple as just
having two batteries that can be switched between each other. As Yukio
says, there's normally a dual charge control box, which does indeed
contain at least isolation diodes. My next door neighbour went through all
this when he converted a van to an RV for touring round Europe. I think it
would be wise to take professional advice from a reputable auto electrical
shop on this one, or at least post the question on one of the auto repair
groups that might have a genuine expert in this field.

Years ago my family had a sailboat with dual batteries and my grandparents
had an RV with a similar setup. In the boat, there was a switch which was
wired to each battery with very heavy cables, it could select 1, 2, or both
in parallel. Only the selected battery would be charged or drawn from. The
RV had a similar switch, but charging was accomplished through an isolator
which was nothing but a couple diodes potted with a large heatsink. Both
were charged simultaneously but the switch selected which one loads draw
from.

30A should be adequate for charging the battery, but it has to be heavy
enough to handle both the charge current and the load current. Either way
talk to RV or boat guys for solid advice on this one, it's a very common
arrangement.

 

[GregS]

I'm about to configure my 97 Plymouth van so that it has two batteries. The
second battery will be kept in the rear of the van in a battery box with a
vent through the floor. I'm using a Mega-Tron RV-Marine Deep Cycle 12v
battery, which will provide power to a medical device at night. I bought a
Valmar (Model 31122) battery selector switch. The switch has four settings:
Off, 1, All and 2. I suspect that 1 means batter 1, and 2 battery 2.

I have a pretty fair idea how to install it ignition and ground wise. I know
the difference between +/-, for example. I'm going to need some wire to go
from the rear to front under the chassis. Does #10 seem right? I'll try to
keep it tight and away from the fuel tank. It seems best to put the switch
inside the engine compartment. I think I'll be able to drill a 1" or so hole
through the floor in the rear of the van. Maybe I'll call the Plymouth and
ask for advice on that. Any suggestions or comments on all this?

I plan to put a 30A fuse inline.

Separating the batteries poses problems. If the battery is cranking the the starter,
you really can't use a fuse. Thats the way its been done for a long time.
Ordinarily I recommed using batteries in parallel. Draining down a battery
reduces life, and with two batteries, there is less sag, improving overall
performance. With the widely separated batteries, using a diode steering
unit is going to be mandatory. In any case, install a battery close fuse, unless it
cranking the starter, and that lead should be as short as possible. There are
race cars and other vehicles using a long starting lead, but its
not common.

greg

 

[mike]

I'm about to configure my 97 Plymouth van so that it has two batteries. The
second battery will be kept in the rear of the van in a battery box with a
vent through the floor. I'm using a Mega-Tron RV-Marine Deep Cycle 12v
battery, which will provide power to a medical device at night. I bought a
Valmar (Model 31122) battery selector switch. The switch has four settings:
Off, 1, All and 2. I suspect that 1 means batter 1, and 2 battery 2.

I have a pretty fair idea how to install it ignition and ground wise. I
know
the difference between +/-, for example. I'm going to need some wire to go
from the rear to front under the chassis. Does #10 seem right? I'll try to
keep it tight and away from the fuel tank. It seems best to put the switch
inside the engine compartment. I think I'll be able to drill a 1" or so
hole
through the floor in the rear of the van. Maybe I'll call the Plymouth and
ask for advice on that. Any suggestions or comments on all this?

I plan to put a 30A fuse inline.

Use a diode isolator. Avaialable at any rv store or auto parts store or
target or wal-mart or K-mart or most any place else.
Switches are a bad idea 'cause eventually, you'll forget and the car
won't start. You also don't want to switch a dead battery across a
charged one. Wears the swtich out big-time...or blows fuses.
Depending on how fast you want to charge the battery, #10 may limit the
current below what you want. Do the math on wire resistance.
Don't forget that sharp metal cuts insulation. Grommet the holes.

Be aware that the hydrogen released during overcharge won't go out the
floor vent. It'll accumulate in the top of the box. Rethink your vent
scheme.

Are we having fun yet?
mike

 

[[email protected]]

Stuff on adding a second battery, snipped.

With respect to you, your life and all the other answers here, keep a
couple of things in mind:

Lead-Acid storage batteries contain HUGE amounts of energy, surrounded
by nasty acid and generating explosive gases. Do not trust half-assed
solutions or take half-assed advice (including mine) without several
pounds of finely ground salt.

Then: Do the set-up right. Use a purpose-built automatic isolation
system. This is one:

http://www.dxengineering.com/Parts.asp?ID=207&PLID=143&SecID=65&DeptID=25&PartNo=DXE-40102

Another:

http://arb.com.au/arb-dual-battery-systems.php

There are more than a few others.

Presumably, these systems are designed to do exactly what you want the
way you want it. And, presumably they will not melt down you or the
battery.

As to venting: Obtain one of the newer batteries with a collective
vent to a hose that you may direct as you wish. My Volvo has the
battery under the floor in the rear, my '87 VW camper has it under the
right front seat, the other '99 VW camper has its second battery
underneath the rear floor (right under the head of the bed). All of
them are connected to such a venting system.

By the way, the battery cables on the Volvo and both VWs are massive,
I would guess the metric equivalent of #4 stranded, at least as thick
as my index finger. The second battery on the '99 camper is a marine-
type and only to run the housekeeping systems while the engine is off.
It charges off the engine as well as a built-in inverter if there is
line-power available. Even though it does not serve as a back-up
starting battery, the cables to it are massive as described.

Peter Wieck
Wyncote, PA

 

[jakdedert]

With respect to you, your life and all the other answers here, keep a
couple of things in mind:

Lead-Acid storage batteries contain HUGE amounts of energy, surrounded
by nasty acid and generating explosive gases. Do not trust half-assed
solutions or take half-assed advice (including mine) without several
pounds of finely ground salt.

Then: Do the set-up right. Use a purpose-built automatic isolation
system. This is one:

http://www.dxengineering.com/Parts.asp?ID=207&PLID=143&SecID=65&DeptID=25&PartNo=DXE-40102

Another:

http://arb.com.au/arb-dual-battery-systems.php

There are more than a few others.

Presumably, these systems are designed to do exactly what you want the
way you want it. And, presumably they will not melt down you or the
battery.

As to venting: Obtain one of the newer batteries with a collective
vent to a hose that you may direct as you wish. My Volvo has the
battery under the floor in the rear, my '87 VW camper has it under the
right front seat, the other '99 VW camper has its second battery
underneath the rear floor (right under the head of the bed). All of
them are connected to such a venting system.

By the way, the battery cables on the Volvo and both VWs are massive,
I would guess the metric equivalent of #4 stranded, at least as thick
as my index finger. The second battery on the '99 camper is a marine-
type and only to run the housekeeping systems while the engine is off.
It charges off the engine as well as a built-in inverter if there is
line-power available. Even though it does not serve as a back-up
starting battery, the cables to it are massive as described.

Peter Wieck
Wyncote, PA

And the venerable MGB has a pair of 6v batteries (in series) under the
back package shelf...properly vented.

I think it's useful to go back to the OP which states that the second
battery in his application is NEVER to be used for starting the vehicle.
That's all well and good, but several posters apparently missed it.

Consequently, a '0' or '00' cable in his case is probably overkill. The
cable would be sized based on the output capacity of the charging
system on his vehicle vs. the expected voltage drop in the length of the
conductor to the second battery. A look under the hood of most vehicles
confirms that that the wire run from the alternator to the battery is
rarely sized above 12ga or so.

That's not to say that a complete rethink of the OP's original setup is
not in order. IMO, either of the above setups would be far superior to
what he originally had in mind. OTOH, a properly engineered system
could be designed to do exactly what he envisioned: provide a clean,
capacious source of 12 volts DC to run *outboard* equipment...said
source to be replenished by the vehicle charging system.

The OP apparently does not have the requisite knowledge or capability to
design such a system, however. Unless that expertise can be purchased
locally, I'd suggest he go with something like the above. What he wants
is theoretically possible, but too difficult to design safely from a
distance.

jak

 

[[email protected]]

Consequently, a '0' or '00' cable in his case is probably overkill. The
cable would be sized based on the output capacity of the charging
system on his vehicle vs. the expected voltage drop in the length of the
conductor to the second battery. A look under the hood of most vehicles
confirms that that the wire run from the alternator to the battery is
rarely sized above 12ga or so.

When I read "medical equipment", the term "overkill" leaps immediately
to mind. Followed by "reliablity" and "caution".

Peter Wieck
Wyncote, PA

 

[jakdedert]

When I read "medical equipment", the term "overkill" leaps immediately
to mind. Followed by "reliablity" and "caution".

Peter Wieck
Wyncote, PA

Granted, thus my recommendation for local examination of the situation
and competent local help. This is not a case where a good determination
can be made remotely.

jak