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ClassicCamper
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PostPosted: Sun Jul 05, 2020 7:58 pm    Post subject: Dual Battery Set-Up Reply with quote

I decided that I am going to hook-up a dual battery system on my 412 Wagon. Due to the fact that I am attempting to install air conditioning and I put heated seat pads under the upholstery.

Here's the plan:

1) Use two fog-light relays, one for the seats, the other for the A/C.

2) Apply switched power from the main battery to actuate both relays when the key is 'on'.

3) Run power to the relay (terminal 30) from the auxiliary battery which will run both the A/C and the seats.

4) Set-up the dual battery relay between the main and aux battery which will allow the aux battery to charge from the alternator AND will cut off the A/C & Seats if the aux battery gets too low. This way, if too much voltage is drained from the aux battery, I'll still have enough power in the main battery to start the car. This is pretty similar to how I have my Westy set-up.

I'll let you know how it works out in case anyone is interested in setting up a second battery for their gas heater, radio/amps etc. I'm pretty sure this will work quite well. Open to feedback/suggestions.
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Lars S
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PostPosted: Sun Jul 05, 2020 9:34 pm    Post subject: Re: Dual Battery Set-Up Reply with quote

Intresting!
Just curoius about the power balance...what is the power input for the AC and heater and what amps does your alternator have?


/Lars S
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raygreenwood
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PostPosted: Mon Jul 06, 2020 7:27 am    Post subject: Re: Dual Battery Set-Up Reply with quote

I know what Lars is asking.....and its an important consideration.

There have been a couple of really good, detailed threads....with wiring diagrams....about dual battery installation. I will see if I can,find them and link them in.

There are several main items to address with a dual battery install:

1. How much initial current/amps draw is allotted to each battery. I think that may be part of what Lars was asking. In other words......whats hooked directly to each battery all the time?

As it is now with everything connected to the one battery.....if you add up potential amps usage.....worst case.....without even having AC....much less a bitchen stereo and seat heaters.....the stock 55 amp alternator at its best.....is just barely enough.

Years ago....looking in on one of these threads....a handful of either bus or vanagon people ...stated the usual....."been running all of this _ _ _ _....on the stock alternator for years and never had an issue"......and then you start getting into where they live (weather), when and how they drive the vehicle, whether the vehicle has any issues, is injected or carbed etc, etc.

I can fully attest.....that if you take any long or even medium trips and treat the car like even a semi-modern car......the stock 55 amp alternator is perilously close to being short on amps.
Its very easy...living in Oklahoma, Texas, Georgia, Kansas.....and other places.....to find plenty of days and nights where the weather is just ahove freezing....its raining.....its night time and you are driving between 45 and 60 mph.

Under those conditions.....you can have all four headlights and markers on, dash defrost fan, wipers on full, gas furnace running and fuel injection/engine running. If you have a stereo.....that even draws 10-15 amps at peak......you will be at the amp limit and will notice that there will be rich running from systems like D and L jet from variable voltage/amperage, you can the headlights go from bright to dim as the blinkers click on and off when idling at a light.....and csn hear the rpm of the fuel pump for the heater go up and down when it should br steady......and certain fuses run warm. This is even without using an AC system....say for defrosting the dront windshield in the modern car manner or using seat heaters.

If you add it up.....under the listed maximum usage conditions.....unless every component and connection in the car is factory perfect pulling exact amperage......and you have bone stock headlights and radio......you are very close to the limit for the stock 55 amp alternator.

This level of usage is also why a lot of the late westfalia/camper bus guys had thr 70 amp alternator option.

So that is the first question. Should you stick with just the 55 amp stock alternator?

This also leads to the second question:

2. If you have the type of amp draw listed above....even before adding a stereo, better headlights....and maybe even seat warmers and runnong AC for defrosting....and you will or already do.......even if you split usage off of some components to seperate batteries.........you are really just playing the "shell game" with a limited resource (amperage).

Sooner or later.....there will be times under cold, wet weather and night time conditions......that both batteries will demand charge from the alternator at the same time.

Can your alternator do that? If not....what mechanism/method do you use to give prioroity to one battery or the other?

More thoughts and links later. Work time. Ray
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vwrenault
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PostPosted: Mon Jul 06, 2020 2:32 pm    Post subject: Re: Dual Battery Set-Up Reply with quote

Here's one I was going to use on my car
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ClassicCamper
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PostPosted: Mon Jul 06, 2020 8:12 pm    Post subject: Re: Dual Battery Set-Up Reply with quote

One item to note on this...the car originally came with air conditioning and still had the compressor on the engine when I picked up the car. Since then, I've rebuilt the under-dash evaporator with a newer, more efficient fan. Also, the old condenser that was attached to the car had two small fans attached to it.

Gilmore Enterprises made me an upgraded condenser that only requires one fan, so I tossed the old condenser.

So, the car at one time operated on one battery with an A/C system, so technically, the only thing I am adding are the seat warmers, which I would not have on in tandem with the A/C. As to the amperage of the alternator, I have no clue. I should have checked when I had the engine out.

Quote:
Can your alternator do that? If not....what mechanism/method do you use to give prioroity to one battery or the other?


The set-up I plan to have (just like my Westy) would have a relay that would isolate the two batteries if the aux battery gets too low. This would protect the driving battery should the A/C / Seats draw too much energy. Worst case scenario, the A/C or seats would simply stop operating and kill the aux battery, but I'd still be able to start the engine.

At least, that's the plan....
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PostPosted: Mon Jul 06, 2020 10:22 pm    Post subject: Re: Dual Battery Set-Up Reply with quote

ClassicCamper wrote:
One item to note on this...the car originally came with air conditioning and still had the compressor on the engine when I picked up the car. Since then, I've rebuilt the under-dash evaporator with a newer, more efficient fan. Also, the old condenser that was attached to the car had two small fans attached to it.

Gilmore Enterprises made me an upgraded condenser that only requires one fan, so I tossed the old condenser.

So, the car at one time operated on one battery with an A/C system, so technically, the only thing I am adding are the seat warmers, which I would not have on in tandem with the A/C. As to the amperage of the alternator, I have no clue. I should have checked when I had the engine out.

Quote:
Can your alternator do that? If not....what mechanism/method do you use to give prioroity to one battery or the other?


The set-up I plan to have (just like my Westy) would have a relay that would isolate the two batteries if the aux battery gets too low. This would protect the driving battery should the A/C / Seats draw too much energy. Worst case scenario, the A/C or seats would simply stop operating and kill the aux battery, but I'd still be able to start the engine.

At least, that's the plan....


Here is the deal. No VW 411 or 412 ever came with air conditioning.

They were dealer installed kits...and the only technical aspect ever put into these cars by the factory that "helped" with the dealer AC install...is the single run of the heavy gauge black and purple wire in the loom to actuate the compressor.

Having driven a 412 with AC...I can tell you that it BARELY has enough power to operate. It causes issues with headlights and with fuel pump, ignition and injection...anything that needs stable voltage. The largest alternator that came in a 411/412 is 55 amps.

You need to add up what could possibly be on at one time...and add about 9-10% for wire ,heat and connection resistance.

From my notes many years ago....Looking at the actual amp draws of everything in the car...actual amp draws....it equals out to about 33% of the fuse rating in each fuse box channel for simple filament items like bulbs etc......and about 50% of fuse rating for high draw items like headlights and heater.

Cut to the chase....everything in the car draws a combined real world 49 amps....at best. With the 10% overage...which is truly there....its right at 53.9 amps.

Of course...you think you will not have all of this on....but the gas furnace draws a ton...far more than it should. Keeping in mind when its running it has two fans plus the 5k rpm one in the dash if its raining and you need defrost. A fuel pump and glow plug and coil.

On a rainy, cold weather night drive.... you have all of that...plus rear window defrost, bright lights and dims, marker lights, wipers, dash lights...occasionally brake lights....heater...license plate lights....fuel pump...injection....coil/ignition.

Yes...you may not run AC for this drive....unless you plan to use it for windshield defrost like a modern car....bit even without AC....and with perfect wiring....you will be at bare minimum 45+ amps.

So its something to think about. Yes....the car will keep running...but as amperage draw gets higher and gets sparse....fuses get hot. Find out exactly how much amperage your fans and AC draw...but I can tell you AC was NOT planned for in these cars in the electrical load. The system is barely adequate.

I'm not saying you should not put in seat heaters or AC.

But.....a larger alternator is something even a 411/412 with no AC could use and is something I have been planning for years.

Ray
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Lars S
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PostPosted: Mon Jul 06, 2020 10:38 pm    Post subject: Re: Dual Battery Set-Up Reply with quote

OK, I thought you were adding an electric AC compressor (sorry my bad english reading).
I have had seat heaters on my own 412 back in the days and with some diciplin in using it it worked fine with just one battery so I think your setup - with some diciplin - have good chanses to work. However my heaters were perhaps not so powerful as yours may be.
About running the AC I have no experience but I would believe it tends to lower the idle at least.
By the way resistance in wiring, connections etc will LOWER the amps used....but on the other hand it may as an example increase the time you have to use the heated rear window as it lowers the power in it.

There were only two alternator sizes from factory 45 and 55 amps and the later one is far more common.


/Lars S
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PostPosted: Tue Jul 07, 2020 12:26 pm    Post subject: Re: Dual Battery Set-Up Reply with quote

Lars S wrote:
OK, I thought you were adding an electric AC compressor (sorry my bad english reading).
I have had seat heaters on my own 412 back in the days and with some diciplin in using it it worked fine with just one battery so I think your setup - with some diciplin - have good chanses to work. However my heaters were perhaps not so powerful as yours may be.
About running the AC I have no experience but I would believe it tends to lower the idle at least.
By the way resistance in wiring, connections etc will LOWER the amps used....but on the other hand it may as an example increase the time you have to use the heated rear window as it lowers the power in it.

There were only two alternator sizes from factory 45 and 55 amps and the later one is far more common.


/Lars S



Yes... i=V/r....yes....being inversely proportional....when you increase voltage, current/amps also increases.

And...if you increase resistance...current drops. The problem is that this is usage of supplied current or amps drops.

The problem is that poor connections.....also cause a drop in voltage....but the actual current demand does not increase from the component. A drop in voltage available increases supplied amperage. The component (especially motors)...run hot. As they heat up they demand more amperage. And...amperage is a finite supply.

But...the battery has a lot of amps available....so it pulls from the battery. What this causes is a lot of constant work from the alternator and lots of cycling from the regulator.

The type 4 regulator run almost red hot all the time from the demand. The biggest issue with running like this the regulators get inaccurate with age...and can start burning out.

The real issue all of this causes is spikes in voltage and current as the system kicks in and out of charge. Its not a frequent enough problem to cause fuel pump issues....but there is a momentary blip as the charging kicks in and out.

In the scheme of things a 1 second blip to the fuel pump voltage is not a huge issue. It become a noticeable issue the coil/ignition and injection feed....with D-jet.

Where all of this comes from...is it depends on how tight your D-jet tuning is. Back when I was driving my 412 60-70k miles a year....I went through a regulator about every 50-60k miles.

Shortly ...usually about 3-4k miles before it burned out....the combination of voltage variation at pump, ignition and injection caused lean spikes and idling issues.

All of that said.....the 45 amp units never made it here. Pretty much everything here was 55 amp.

And in general....I think he is going to be fine with the 55 amp unit. But I think its limiting because with either the AC or Gas heater running at night with light and with wipers....he is running at 80% all the time.

But I recognize the "improvement" pattern Wink Laughing ...he is just like me.

What discerning type 4 owner wouldn't want AC if it came with it....and who wouldn't ant the gas heater with all the bell and whistles....and if seat heater kits had been available back in teh day....I would have had them too! Laughing

But...on that same pattern.....I was running 55/65 H-4's with 100 watt HB-2 high beams. No way with all of my night driving I'm not installing better headlight...right?
And I have always had a killer, fine sounding stereo with right at 70 watts nominal/100 watts per channel. Thats another 17 amps.

Back in the day....I had maybe 50 watt channel ...about 8 amps peak...but the headlights were hard on it.

You should see what I have purchased in the past year for the stereo in my 412.....it will sound so fine Very Happy

Also.....all of this brings on the good conversation to have.


The stock alternator can work all of this just fine....depending on what you have isolated to each battery.

For example. Lets say you keep battery #1 running all of the lights, engine, fuel....all the normal stiff....EXCEPT say the high beams and the gas heater. The brights and heater run off of battery #2.

So while driving at night and using the gas heater...you are pulling intermittent use of brights and heater from #2c and .the #2 battery only charges when needed. This does not affect running or low beam lights except for an occasional blip as the charging kicks in. All is good.

When stopped and not running....no high beam usage...you can run the gas heater...from my real world experience.....for about 3 hours...before the voltage drops enough to affect the blower and therefore fuel pump and ignition speed. So you start and run for 10-15 minutes to charge battery #2 and all is good.

I found this out back in 1999...when I got stranded in a long traffic knot on a highway in a freak snowstorm that dumped 10" of snow. Sat there for almost 12 hours.....running the gas heater and then fast idling for 20 minutes every 3 hours. Worked like a champ. I only had the one battery though.

On a related thought....voltage wise. Our ignition and especially fuel injection and heater output ...are all voltage sensitive. As voltage drops....fuel mixture richens up with D-jet. I always though it would be SMART....to have a voltage stabilizer/rectifier for the fuel injection and fuel pump circuit ....like many of the industrial machine I come in contact with.

But....they were very expensive...and big....20 years ago. I have recently found a good company that makes very small..solid state DC voltage stabilizers for 12 volt with a wide range of amperage rates.

These are in the $50-60 range. I ill post those links in this thread. Ray
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PostPosted: Tue Jul 07, 2020 7:29 pm    Post subject: Re: Dual Battery Set-Up Reply with quote

Quote:
So while driving at night and using the gas heater...you are pulling intermittent use of brights and heater from #2c and .the #2 battery only charges when needed. This does not affect running or low beam lights except for an occasional blip as the charging kicks in. All is good.


Brilliant idea, Ray. I think this is what I'm going to do. I'll add the brights to the battery number two and see how this works.

This is a great thread, with really good input. I'm going to report back and let you know how it works.
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PostPosted: Wed Jul 08, 2020 1:01 am    Post subject: Re: Dual Battery Set-Up Reply with quote

raygreenwood wrote:


Yes... i=V/r....yes....being inversely proportional....when you increase voltage, current/amps also increases.

And...if you increase resistance...current drops. The problem is that this is usage of supplied current or amps drops.

The problem is that poor connections.....also cause a drop in voltage....but the actual current demand does not increase from the component. A drop in voltage available increases supplied amperage. The component (especially motors)...run hot. As they heat up they demand more amperage. And...amperage is a finite supply. ....
....Ray


Ray, I agree to most of what you write in your last post but not to the quoted part above.

I argue that DC motors (with brush) as in our 411/412s will REDUCE the amps if voltage is reduced. To prove my statement I made at practical test at my bench today, I ran a 411 heater fan (the fan in the engine compartment) at different voltages, here are the results:
12,5V 7,6 Amps
10,3V 6.4 Amps
8,5V 5,7 Amps
5,1V 3,3 Amps
As you see the current (Amps) is almost propotional to the voltage, I would say this is valid for all electrical components in a 411/412 (light bulbs, heated window, electrical motors).
For AC induction (asynchronus) motors (normal industrial AC motors) your statement is correct Ray, they tend to increase their current draw (and heats up) when voltage is reduced (within limits).

I also made a list of the normal current draw at 12 - 13V for most of the electrical components in a 411/412. It can be good to know where all the current goes Smile
Figures are approximate and comes from my own tests and some from litterature.
-Fuel pump 1,9 Amps
-Ignition 1,5 Amps
-High beams 9 Amps (total of both lamps)
-Low beams 6 Amps (total of both lamps)
-Tail, licence, side markers, parking lights etc 5 Amps (total of all lamps)
-Heater fan 7,6 Amps
-Eberspächer fan 6,5 Amps (fan only)
-Rear window 6,5 Amps
-Windshield vipers 4/6 Amps (half /full speed, current fluctuating with wiper arm moement)
-Fresh air fan 2,2/3,3 Amps (half /full speed)

/Lars S
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VW411 2-d -70, White, sold Sad
VW412 4-d, -73, Gold Metallic, daily driver
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Suzuki K50, -77, Black, daily driver
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PostPosted: Wed Jul 08, 2020 11:43 am    Post subject: Re: Dual Battery Set-Up Reply with quote

Lars S wrote:
raygreenwood wrote:


Yes... i=V/r....yes....being inversely proportional....when you increase voltage, current/amps also increases.

And...if you increase resistance...current drops. The problem is that this is usage of supplied current or amps drops.

The problem is that poor connections.....also cause a drop in voltage....but the actual current demand does not increase from the component. A drop in voltage available increases supplied amperage. The component (especially motors)...run hot. As they heat up they demand more amperage. And...amperage is a finite supply. ....
....Ray


Ray, I agree to most of what you write in your last post but not to the quoted part above.

I argue that DC motors (with brush) as in our 411/412s will REDUCE the amps if voltage is reduced. To prove my statement I made at practical test at my bench today, I ran a 411 heater fan (the fan in the engine compartment) at different voltages, here are the results:
12,5V 7,6 Amps
10,3V 6.4 Amps
8,5V 5,7 Amps
5,1V 3,3 Amps
As you see the current (Amps) is almost propotional to the voltage, I would say this is valid for all electrical components in a 411/412 (light bulbs, heated window, electrical motors).
For AC induction (asynchronus) motors (normal industrial AC motors) your statement is correct Ray, they tend to increase their current draw (and heats up) when voltage is reduced (within limits).

I also made a list of the normal current draw at 12 - 13V for most of the electrical components in a 411/412. It can be good to know where all the current goes Smile
Figures are approximate and comes from my own tests and some from litterature.
-Fuel pump 1,9 Amps
-Ignition 1,5 Amps
-High beams 9 Amps (total of both lamps)
-Low beams 6 Amps (total of both lamps)
-Tail, licence, side markers, parking lights etc 5 Amps (total of all lamps)
-Heater fan 7,6 Amps
-Eberspächer fan 6,5 Amps (fan only)
-Rear window 6,5 Amps

/Lars S



You overall amp draw list is pretty close to mine. It about 80% of availability.

For your heater fan test....yes....true....but you are reducing supplied voltage from the source....with a DC motor that is designed for variable load and voltage.

DC motors like fuel pumps are designed for constant speed and torque at a specific current and amp rate. The load they are carrying...fuel pressure for instance...does not instantly reduce as voltage and current becomes variable.

They are constantly trying to supply constant design rate at load....and draw more current to do so.

Also the problem I was getting at...is that really poor connections become a "resistive" load. They drop voltage and have some amperage load. Bluntly...they "masquerade" as an inline component.

While they may reduce voltage to items like the heater fan...slowing them down and reducing current draw at an inverse proportion....the poor connections have their own current draw....so the benefit of reduced voltage will be a "wash" or worse.

I found that for example....just cleaning up the wiper system by hanging to a smoother, lower viscosity grease and reducing the load by polishing the shafts....and cleaning up grounds and connectors under the dash....cleaning and perfectly connecting ground braids....properly grounding and cleaning relay contacts.....can cut amperage draw by about 3-5 amps. Ray
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PostPosted: Thu Jul 09, 2020 12:29 am    Post subject: Re: Dual Battery Set-Up Reply with quote

raygreenwood wrote:



You overall amp draw list is pretty close to mine. It about 80% of availability.

Ray

Yes, I have now also added windshield wipers and fresh air to the list above.
The alternator gives it max output from approx 2700 engine rpm but at 1000 engine rpm the output is only something like 35Amps (for a fully fresh alternator/regulator).



raygreenwood wrote:

For your heater fan test....yes....true....but you are reducing supplied voltage from the source....with a DC motor that is designed for variable load and voltage.

DC motors like fuel pumps are designed for constant speed and torque at a specific current and amp rate. The load they are carrying...fuel pressure for instance...does not instantly reduce as voltage and current becomes variable.

They are constantly trying to supply constant design rate at load....and draw more current to do so.
Ray

Do not agree here, the DC motors do not draw more current to try to supply their design rate if voltage drops (example due to bad connections) - they reduce their speed, amps and power.
The fuel pump is no different, at full voltage 13,5Volts my pump draws 2,65 Amp, when I reduce the voltage to 11,5 volts the curent falls to 2,31 Amp and one can hear that the pump rpm is lower.

However if you put more load on the motor (running the wipers on a dry windshield) with no change in voltage, the Amps will go up...but thats a different story.




raygreenwood wrote:

Also the problem I was getting at...is that really poor connections become a "resistive" load. They drop voltage and have some amperage load. Bluntly...they "masquerade" as an inline component.

While they may reduce voltage to items like the heater fan...slowing them down and reducing current draw at an inverse proportion....the poor connections have their own current draw....so the benefit of reduced voltage will be a "wash" or worse.

Ray

Ray, I dont se how bad connections can have "their own current draw", everything is connected in serial in a "closed circuit", (from the battery + through the fuse and the switch/relay and connectors etc through the motor windings and back through earth to the battery minus)....the same Amp must flow in the whole circuit....or?





raygreenwood wrote:


I found that for example....just cleaning up the wiper system by hanging to a smoother, lower viscosity grease and reducing the load by polishing the shafts....and cleaning up grounds and connectors under the dash....cleaning and perfectly connecting ground braids....properly grounding and cleaning relay contacts.....can cut amperage draw by about 3-5 amps. Ray

I think what happened here is that you reduced the load for the wiper motor by greasing the mechanical side of it - then the Amps where reduced.
When I tested to run the wipers on full speed on a dry windshield i drew about 6Amps and when I flip the wiper arms up in the air the currend fell to 3,5 Amps.
Your cleaning of the connectors and ground points in fact made the Amps go up since the wiper motor runs on a higher voltage but the reduction from the mechanical greasing was much bigger.

In fact VW used "intentional voltage drop" Smile to make the fresh air fan run at a lower speed, the 2 Ohm, resistor mounted at the back of the fan brings the voltage over the motor down to about 8,5Volts reducing the amps from 3.3 (full speed) to 2.2 (low speed).


/Lars S



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Porsche 914 -72, Bahia Red daily driver Smile
VW411 2-d -70, White, sold Sad
VW412 4-d, -73, Gold Metallic, daily driver
Suzuki T500, -69, Candy Gold, sold Sad
Suzuki K50, -77, Black, daily driver
BMW R69S -69, White, sold Sad
Husqvarna 118cc, -47, Black, Sold Sad
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