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Old 03-04-2015, 09:12 AM   #1
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Best Design for a Separate House & Starting Battery System?

Scalff77's recent video on the Surepower separator and his depiction of the manual override switch made me think of something that has bothered me since I started designing and half-way implementing my 12vdc house electrical system.

In Scalff77's manual override switch diagram he has the house battery negative post connected to the starting battery negative battery post.

But theoretically when designing and installing a house 12vdc system, the solar and the shore power charger and (if so equiped) a second engine alternator dedicated solely to the house system would not need to be connected to the van chassis/frame/body or to the starting battery whatsoever. All negatives can be run back to the house battery post. This is consistant with having a two alternator set up (I have burned up so many alternators that I don't want my starting alternator to burn up a diode when starting the vehicle trying to charge a depleted 250Ah house battery - our fuel pumps are electric).

Because of their outstanding quality I have installed (really only half-installed) a lot of Blue Sea boat components. From my reading about boats, nothing is grounded to the hull which is often fiberglass. (Viva correct me if I am wrong.) All negatives are run back to the negative battery post.

So, assuming that I am not using a Surepower or other separator and have completely separate house and starting battery/charging systems, should I:

1. Connect the house battery negative post to the starting battery negative post?

2. Or should I not connect the house and starting negative posts together?

3. Ground my house battery and my house 12v components to the chassis/frame/body?

4. Or run all my house battery 12v negatives back to the house battery?

5. Ground my house battery to the van chassis/frame/body?

6. Or not ground the house battery to the van chassis/frame/body?

7. Alot of these shunt type battery monitoring devices like Victron Energy's BMV600S are installed on the negative post on the battery. Are their readings messed up when the negative posts on the house and starting batteries are connected?

8. Is a PWM or MPPT solar charge controller confused when the positive lead is going to the house battery and the house battery is not connected to the starting battery, but the negative battery posts on the house batteries and the starting batteries are connected?

Do any of the above answers change if the 12vdc house battery system is grounded to or not grounded at all to the van's chassis/frame/body?

I guess in summary what is the best way to wire a completely separated house and starting battery system?

Thank you.
E350 (formerly aka "Learning slowly..." currently aka "Confusion abounds...")
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Old 03-04-2015, 01:30 PM   #2
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Re: Best Design for a Separate House & Starting Battery Syst

Quote:
Originally Posted by E350

So, assuming that I am not using a Surepower or other separator and have completely separate house and starting battery/charging systems, should I:

1. Connect the house battery negative post to the starting battery negative post?

2. Or should I not connect the house and starting negative posts together?

3. Ground my house battery and my house 12v components to the chassis/frame/body?

4. Or run all my house battery 12v negatives back to the house battery?

5. Ground my house battery to the van chassis/frame/body?

6. Or not ground the house battery to the van chassis/frame/body?

Alot of these shunt type battery monitoring devices like Victron Energy's BMV600S are installed on the negative post on the battery. Are their readings messed up when the negative posts on the house and starting batteries are connected?

Is a PWM or MPPT solar charge controller confused when the positive lead is going to the house battery and the house battery is not connected to the starting battery, but the negative battery posts on the house batteries and the starting batteries are connected?

Do any of the above answers change if the 12vdc house battery system is grounded to or not grounded at all to the van's chassis/frame/body?

I guess in summary what is the best way to wire a completely separated house and starting battery system?

Thank you.
E350 (formerly aka "Learning slowly..." currently aka "Confusion abounds...")
The short answer is 1-6 will all work fine.

Longer answers are:

1. On a schemtic, it may be shown this way but in reality they are both typically tied to the chassis somewhere......the chassis is a ground buss.....think of it as a giant fat wire.

2. See the answer to 1. above.

3. Sure, no problem, then both systems share a common ground (the chassis)

4. You will have to do this if you do not tie the house batteries to the chassis/body. If you ground the house -ve post to the chassis, you can either run individual negative conductors back to the house battery or just connect negatives to the chassis. Not grounding the battery -ve technically requires twice the wires compared to grounding it, manufacturers like to save pennies, so they use the chassis as a ground; this also makes for simpler wiring.

In designing audio stuff, this mix of grounds can create ground loops which make hum, but will probably not matter in your van....

5. See the answer to 4. above.

6. Same as 5 above.
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Old 03-04-2015, 01:46 PM   #3
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Re: Best Design for a Separate House & Starting Battery Syst

boywonder: Thanks! I added numbers to the following items in my previous post:

7. Alot of these shunt type battery monitoring devices like Victron Energy's BMV600S are installed on the negative post on the battery. Are their readings messed up when the negative posts on the house and starting batteries are connected?

8. Is a PWM or MPPT solar charge controller confused when the positive lead is going to the house battery and the house battery is not connected to the starting battery, but the negative battery posts on the house batteries and the starting batteries are connected?

If I ground to the chassis/frame/body or even connect the negative battery posts on the house and and starting batteries together. How is it that these monitoring devices which are attached to the ground in items numbers 7 and 8 aren't confused when there are multiple charging/discharging sources?

I was recently reminded of a statement made to be by an examiner during an exam where he told me in front of the other examinees: "Remember Tim, there are no stupid questions, only stupid people asking questions..."
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Old 03-04-2015, 01:47 PM   #4
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Re: Best Design for a Separate House & Starting Battery Syst

...let's talk about grounds and voltage potential........

Conceptually, if I ground the -ve lead of my 12v battery to ground and put a voltmeter between the +ve and -ve terminals, I get 12v. This is also 12v with respect to ground.

Then for giggles lets wire two 12v batteries in series (-ve terminal of battery A to ground and +ve terminal of battery A to -ve terminal of battery B).

If I now measure the voltage potential from battery A's + terminal to ground I get 12V. So battery A's +ve terminal is 12v with respect to ground.

If I measure the voltage from battery B's +ve terminal to ground I get 24V (since they are "stacked" ie series wired).....So battery B's positive terminal is 24V with respect to ground.

If I measure the voltage from battery A's +'ve terminal (or battery B's -ve terminal; they are connected together) to battery B's +ve terminal, I get 12V.....So battery B's +ve terminal is 24V with respect to ground, and 12V with respect to battery A's positive terminal.

So connecting all of your grounds together creates a "common ground", which is a ground reference for all of the voltages in the van, which is 12V.

Leaving the house battery ground "floating" ie not connected to the starting battery's ground just means that your house stuff ground is not related to the van's ground.

If you are expecting the second alternator to charge the house batts you will probably discover that the -ve side of the house battery will be common grounded with the van battery.

I'm puzzled why you wouldn't want to use a battery separator?....
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Old 03-04-2015, 01:51 PM   #5
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Re: Best Design for a Separate House & Starting Battery Syst

Quote:
Originally Posted by E350

8. Is a PWM or MPPT solar charge controller confused when the positive lead is going to the house battery and the house battery is not connected to the starting battery, but the negative battery posts on the house batteries and the starting batteries are connected?
No, it's not confused. If the +ve terminals of the batteries are not connected together, then the solar is charging only the house battery. If the +ve terminals are connected (like with a separator or just wired together) then the solar (or alternator or shore charger or whatever) will be charging both van and house batteries.
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Old 03-04-2015, 01:56 PM   #6
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Re: Best Design for a Separate House & Starting Battery Syst

My van has gone through at least three alternators that I can remember.

One memorable occasion was having my alternator die while driving at night on a mountain road in a snow storm after jump starting someone else's vehicle in the ski area parking lot.

Sportsmobile installed a separator when I had them put the roof on. When that alternator died I asked Lehr Auto Electric (been around since 1945 and do the electrical systems on ambulance and police vehicles) what the heck was going wrong and they pointed to that separator and told me that I have a starting alternator which is best paired with a quick charging starting battery and that it was working too hard to charge the slow charging deep cycle 250Ah house battery.

I don't know if what they said was true or not. I have not researched alternators. It would not surprise me though that Ford would not overbuild the alternator which need only recharge a starting battery such that it could routinely recharge a depleted 250Ah or greater deep cycle house battery. That would seem to violate some economic aspect of engineering design... But that's just a WAG on my part.

I am curious if anyone else has experienced premature alternator failure after it has been repurposed to additionally recharge a large deep cycle house battery?

(I think I threw that separator away some time ago otherwise if I find it I will offer it free for postage.)
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