Auto battery isolator question

[Keith]

I have set up an inverter for 120-volt use in a service van. I have
used a commercial (RV supply house) battery isolator to separate the
inverter's battery from the vehicle's battery. The problem comes from
the vehicle's alternator needing to see battery voltage to begin
charging - in other words the alternator is self initiating, and only
has a "status" out wire (for lack of a better term and the high
amperage terminal. Now, because the isolator, umm, isolates everything
from everything, the alternator won't charge unless I jump it to the
vehicle's battery. This means, however, the inverter also will draw
from the vehicle battery, which defeats the purpose of the second
battery and isolator. I know I can play with contactors etc, to connect
the charging system as needed, but any ideas on how to do it "right"
using solid state stuff? Have I got the wrong type of isolator?

Keith

 

[Dbowey]

Keith posted:
<< I have set up an inverter for 120-volt use in a service van. I have
used a commercial (RV supply house) battery isolator to separate the
inverter's battery from the vehicle's battery. The problem comes from
the vehicle's alternator needing to see battery voltage to begin
charging - in other words the alternator is self initiating, and only
has a "status" out wire (for lack of a better term and the high
amperage terminal. Now, because the isolator, umm, isolates everything
from everything, the alternator won't charge unless I jump it to the
vehicle's battery. This means, however, the inverter also will draw
from the vehicle battery, which defeats the purpose of the second
battery and isolator. I know I can play with contactors etc, to connect
the charging system as needed, but any ideas on how to do it "right"
using solid state stuff? Have I got the wrong type of isolator?
I believe your isolator may be mis-wired.

In my motorhome the isolator does not affect how the vehicle system operates:
The vehicle battery is always available to vehicle load and the alternator.
When the engine is not running, the isolator isolates the rear battery from the
vehicle battery. When the engine is running, it connects the rear battery in
parallel with the vehicle battery.

Don

 

[Rodney Kelp]

What about when your boondocking generator is running? Does it also charge
all the batteries?

I believe your isolator may be mis-wired.

In my motorhome the isolator does not affect how the vehicle system
operates:
The vehicle battery is always available to vehicle load and the
alternator.
When the engine is not running, the isolator isolates the rear battery
from the
vehicle battery. When the engine is running, it connects the rear battery
in
parallel with the vehicle battery.

Don

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[Bill Bowden]

Keith <keithrol@ixpres.com> wrote in message news:<40fc59f3_1@news.vic.com>...

I have set up an inverter for 120-volt use in a service van. I have
used a commercial (RV supply house) battery isolator to separate the
inverter's battery from the vehicle's battery. The problem comes from
the vehicle's alternator needing to see battery voltage to begin
charging - in other words the alternator is self initiating, and only
has a "status" out wire (for lack of a better term and the high
amperage terminal. Now, because the isolator, umm, isolates everything
from everything, the alternator won't charge unless I jump it to the
vehicle's battery. This means, however, the inverter also will draw
from the vehicle battery, which defeats the purpose of the second
battery and isolator. I know I can play with contactors etc, to connect
the charging system as needed, but any ideas on how to do it "right"
using solid state stuff? Have I got the wrong type of isolator?

Keith

You can make an isolator with single diode and just put
the diode is series with the spare battery. The only problem
is the diode will drop about 0.7 volts so the spare battery will
never fully charge. The regulator keeps the voltage of the main
battery around 14 volts, so the spare battery will limit to
around 13, but that may not be a problem. It should be fairly well
charged (maybe 75%) at 13 volts.

You need a high current diode rated at 25 amps or more. An
old diode out of an alternator should work. Connect the
cathode of the diode to the spare battery (+) terminal and
the anode to the (+) terminal of the main battery. Current
will only flow one way through the diode, so the only discharge
path will be through the inverter.

-Bill

 

[Bill Bowden]

Keith <keithrol@ixpres.com> wrote in message news:<40fc59f3_1@news.vic.com>...

I have set up an inverter for 120-volt use in a service van. I have
used a commercial (RV supply house) battery isolator to separate the
inverter's battery from the vehicle's battery. The problem comes from
the vehicle's alternator needing to see battery voltage to begin
charging - in other words the alternator is self initiating, and only
has a "status" out wire (for lack of a better term and the high
amperage terminal. Now, because the isolator, umm, isolates everything
from everything, the alternator won't charge unless I jump it to the
vehicle's battery. This means, however, the inverter also will draw
from the vehicle battery, which defeats the purpose of the second
battery and isolator. I know I can play with contactors etc, to connect
the charging system as needed, but any ideas on how to do it "right"
using solid state stuff? Have I got the wrong type of isolator?

Keith

You can make an isolator with single diode and just put
the diode is series with the spare battery. The only problem
is the diode will drop about 0.7 volts so the spare battery will
never fully charge. The regulator keeps the voltage of the main
battery around 14 volts, so the spare battery will limit to
around 13, but that may not be a problem. It should be fairly well
charged (maybe 75%) at 13 volts.

You need a high current diode rated at 25 amps or more. An
old diode out of an alternator should work. Connect the
cathode of the diode to the spare battery (+) terminal and
the anode to the (+) terminal of the main battery. Current
will only flow one way through the diode, so the only discharge
path will be through the inverter.

-Bill

 

[Keith]

Bill Bowden wrote:

Keith <keithrol@ixpres.com> wrote
I have set up an inverter for 120-volt use in a service van. I have
used a commercial (RV supply house) battery isolator to separate the
inverter's battery from the vehicle's battery. The problem comes from
[...]

only flow one way through the diode, so the only discharge
path will be through the inverter.

Therein lies the rub. I do not want the vehicle battery to feed the
inverter at all. I do want the vehicle charging system to charge the
inverter's separate battery. With a diode, or the isolator (which is I
suspect just 2 90-amp rated diodes in a heatsink case) using just 1 of
it's diodes, the inverter will pull current from the vehicle's battery
through the diode, yes?

I realise I should have described the isolator in my post. It is just a
simple 3-terminal metal encased unit. Alternator output goes to the
center termainl, and each battery positive goes to one the other
terminals. It's rated at 90 amps continuous.

Keith

 

[Rich Grise]

Keith wrote:

Bill Bowden wrote:

Keith <keithrol@ixpres.com> wrote
I have set up an inverter for 120-volt use in a service van. I have
used a commercial (RV supply house) battery isolator to separate the
inverter's battery from the vehicle's battery. The problem comes from
[...]

only flow one way through the diode, so the only discharge
path will be through the inverter.

Therein lies the rub. I do not want the vehicle battery to feed the
inverter at all. I do want the vehicle charging system to charge the
inverter's separate battery. With a diode, or the isolator (which is I
suspect just 2 90-amp rated diodes in a heatsink case) using just 1 of
it's diodes, the inverter will pull current from the vehicle's battery
through the diode, yes?

I realise I should have described the isolator in my post. It is just a
simple 3-terminal metal encased unit. Alternator output goes to the
center termainl, and each battery positive goes to one the other
terminals. It's rated at 90 amps continuous.

Find an RV show. A guy I used to know years ago sold battery isolators
specifically designed for RVs. They have all kinds of stuff that will
do exactly what you need, probably better than what you (or most of
us, for that matter) could come up with. There's some really cool stuff
at these shows - but it's a niche market, so you don't hear much about
it. Stuff like satellite antenna aimers - a motorized swivel mount with
elevation, to get satellite tv in your RV. I think they even have them
that will track the satellite while you're in motion. A fun place to
visit anyway - same class of people as hamfests and computer flea
markets and stuff. (or the county fair! )
--
Cheers!
Rich

 

[Jamie]

Diode?


Keith wrote:

I have set up an inverter for 120-volt use in a service van. I have
used a commercial (RV supply house) battery isolator to separate the
inverter's battery from the vehicle's battery. The problem comes from
the vehicle's alternator needing to see battery voltage to begin
charging - in other words the alternator is self initiating, and only
has a "status" out wire (for lack of a better term and the high
amperage terminal. Now, because the isolator, umm, isolates everything
from everything, the alternator won't charge unless I jump it to the
vehicle's battery. This means, however, the inverter also will draw
from the vehicle battery, which defeats the purpose of the second
battery and isolator. I know I can play with contactors etc, to connect
the charging system as needed, but any ideas on how to do it "right"
using solid state stuff? Have I got the wrong type of isolator?

Keith

 

[Bill Bowden]

Keith <keithrol@ixpres.com> wrote in message news:<40fcf2bf_1@news.vic.com>...

Bill Bowden wrote:

Keith <keithrol@ixpres.com> wrote
I have set up an inverter for 120-volt use in a service van. I have
used a commercial (RV supply house) battery isolator to separate the
inverter's battery from the vehicle's battery. The problem comes from
[...]

only flow one way through the diode, so the only discharge
path will be through the inverter.

Therein lies the rub. I do not want the vehicle battery to feed the
inverter at all.

Yes, that's right, the inverter would pull current from the
main battery as soon as the spare battery voltage dropped.
I think your isolator with 2 diodes should prevent that.
It should be working correctly now since the inverter cannot
pull current from the main battery.

Why do you think it's not working?

-Bill

 

[Keith]

I have set up an inverter for 120-volt use in a service van. I have
used a commercial (RV supply house) battery isolator to separate the
inverter's battery from the vehicle's battery. The problem comes from
[...]
only flow one way through the diode, so the only discharge
path will be through the inverter.

Therein lies the rub. I do not want the vehicle battery to feed the
inverter at all.

Yes, that's right, the inverter would pull current from the
main battery as soon as the spare battery voltage dropped.
I think your isolator with 2 diodes should prevent that.

It will. But...

It should be working correctly now since the inverter cannot
pull current from the main battery.

It also prevents the main battery to flow to the alternator to enable it
to start charging. The alternator is self-exciting, and needs to see
battery voltage at it's output terminal to start charging. Older
alternators used a separate field wire, made live when the key is on.
On this Dodge Sprinter Van, AKA Mercedes Benz, the alternator has no
explicit input to supply initial current, as far as I can tell. As zoon
az zhes aspinnin, zhes a chargin.

Why do you think it's not working?

*Sound of claxon in background* "Warning! Battery is not being charged
by alternator!"

And by voltmeter check of charging current.

Thanks!

KR

 

[Don Kelly]

"Keith" <keithrol@ixpres.com> wrote in message
news:40fcf2bf_1@news.vic.com...

Bill Bowden wrote:

Keith <keithrol@ixpres.com> wrote
I have set up an inverter for 120-volt use in a service van. I have
used a commercial (RV supply house) battery isolator to separate the
inverter's battery from the vehicle's battery. The problem comes from
[...]

only flow one way through the diode, so the only discharge
path will be through the inverter.

Therein lies the rub. I do not want the vehicle battery to feed the
inverter at all. I do want the vehicle charging system to charge the
inverter's separate battery. With a diode, or the isolator (which is I
suspect just 2 90-amp rated diodes in a heatsink case) using just 1 of
it's diodes, the inverter will pull current from the vehicle's battery
through the diode, yes?

I realise I should have described the isolator in my post. It is just a
simple 3-terminal metal encased unit. Alternator output goes to the
center termainl, and each battery positive goes to one the other
terminals. It's rated at 90 amps continuous.

The isolator should keep the batteries independent. It is designed to do so.
The isolator will have 2 diodes feeding the two batteries from the common
alternator terminal. Where is the "status??" wire normally connected? Is it
normally connected to the hot of the alternator (or, with no isolator- to
the same place- the battery terminal? You should have no problem with this.

--
Don Kelly
dhky@peeshaw.ca
remove the urine to answer

Keith

 

[Keith]

Don Kelly wrote:

The isolator should keep the batteries independent. It is designed to do so.
The isolator will have 2 diodes feeding the two batteries from the common
alternator terminal. Where is the "status??" wire normally connected? Is it
normally connected to the hot of the alternator (or, with no isolator- to
the same place- the battery terminal?

The status wire is connected to a separate terminal on the alternator.

Yes, the isolator will keep the 2 batteries separate. It also prevents
current flow back into the alternator from either battery. This would
normally be a desirable thing, but this alternator needs to see battery
voltage at it's output terminal before it will charge.

Hmmm... I'm wondering if it needs to see full voltage. Maybe I could
use a small resistor to provide a little current to get it charging. I
mean like really small, in the order of 1K ohms. Then if it would start
charging, the power dissapated by the charging current through the
resistor would be very small.

More expirimenting is called for this weekend!

Keith

 

[Watson A.Name \"Watt Sun]

Bill Bowden wrote:

Keith <keithrol@ixpres.com> wrote in message news:<40fc59f3_1@news.vic.com>...

I have set up an inverter for 120-volt use in a service van. I have
used a commercial (RV supply house) battery isolator to separate the
inverter's battery from the vehicle's battery. The problem comes from
the vehicle's alternator needing to see battery voltage to begin
charging - in other words the alternator is self initiating, and only
has a "status" out wire (for lack of a better term and the high
amperage terminal. Now, because the isolator, umm, isolates everything
from everything, the alternator won't charge unless I jump it to the
vehicle's battery. This means, however, the inverter also will draw
from the vehicle battery, which defeats the purpose of the second
battery and isolator. I know I can play with contactors etc, to connect
the charging system as needed, but any ideas on how to do it "right"
using solid state stuff? Have I got the wrong type of isolator?

Keith

You can make an isolator with single diode and just put
the diode is series with the spare battery. The only problem
is the diode will drop about 0.7 volts so the spare battery will
never fully charge. The regulator keeps the voltage of the main
battery around 14 volts, so the spare battery will limit to
around 13, but that may not be a problem. It should be fairly well
charged (maybe 75%) at 13 volts.

You need a high current diode rated at 25 amps or more. An
old diode out of an alternator should work. Connect the
cathode of the diode to the spare battery (+) terminal and
the anode to the (+) terminal of the main battery. Current
will only flow one way through the diode, so the only discharge
path will be through the inverter.

-Bill

From my understanding, the high current diodes used in isolators are
schottky, so the voltage drop is not very much, maybe only a half volt
or less depending on the current.

 

[Don Kelly]

"Keith" <keithrol@ixpres.com> wrote in message
news:40fe421f$1_2@news.vic.com...

Don Kelly wrote:

The isolator should keep the batteries independent. It is designed to do
so.
The isolator will have 2 diodes feeding the two batteries from the
common
alternator terminal. Where is the "status??" wire normally connected?
Is it
normally connected to the hot of the alternator (or, with no isolator-
to
the same place- the battery terminal?

The status wire is connected to a separate terminal on the alternator.

Yes, the isolator will keep the 2 batteries separate. It also prevents
current flow back into the alternator from either battery. This would
normally be a desirable thing, but this alternator needs to see battery
voltage at it's output terminal before it will charge.

Hmmm... I'm wondering if it needs to see full voltage. Maybe I could
use a small resistor to provide a little current to get it charging. I
mean like really small, in the order of 1K ohms. Then if it would start
charging, the power dissapated by the charging current through the
resistor would be very small.

More expirimenting is called for this weekend!

Keith

Have you tried connecting the "status" wire to the alternator terminal. I
would suspect that it is a field wire and the voltage/current controller is
built into the alternator.
Otherwise your resistor idea might work- If the status wire is not connected
to the main alternator output in any way then a resistor should not be
needed. Automotive wiring is a mystifying thing- often with little logic
except- "Oh gee, if I make this shortcut, we can save a penny per vehicle"
I lost two alternators in a '75 VW van due to such a shortcut.
--
Don Kelly
dhky@peeshaw.ca
remove the urine to answer