Power question

Submitted: Tuesday, Mar 11, 2008 at 11:01
ThreadID: 55424 Views:2023 Replies:6 FollowUps:11
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Hi All,
I have enough electrical knowledge to get myself into trouble so I thought I would check with the experts on this forum.

Does anyone have a circuit diagram on how to wire up house batteries to 3 charging sources:

i. vehicle alternator
ii. solar panels
iii. output from a battery charger

While the wiring up seems streight forward, is there any likelihood of damage to one charging device if another is feeding the batteries at the same time?

Do they need to be isolated from each other

E.G. if the alternator is running and feeding the batteries, could this damage the voltage regulator from the solar panels or the battery charger (and all the other combinations)

Rgds
Ian
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Reply By: Ray - Tuesday, Mar 11, 2008 at 14:51

Tuesday, Mar 11, 2008 at 14:51
I personally would not try it. I have three charging systems but each is isolated from the other.
AnswerID: 292098

Reply By: Member - Mike DID - Tuesday, Mar 11, 2008 at 15:45

Tuesday, Mar 11, 2008 at 15:45
All charging sources have to work when a voltage is apllied to their output i.e a battery.

The one exception would be a Shunt-type solar regulator - it will divert current into a load when the voltage gets too high.

You can leave the car connection on permanently.

You can leave the solar regulator connected permanently (provided its not the shunt type).

The Mains Charger I would only connect to the battery when plugged in to 240 volt. Some chargers could draw a small current from the battery if they are not connected to 240 volts.
AnswerID: 292102

Follow Up By: Member - Noldi (WA) - Tuesday, Mar 11, 2008 at 21:04

Tuesday, Mar 11, 2008 at 21:04
Hi Mike R

Thanks for that, my question sounds pretty stupid now that you mention it I put it down to old age

Rgds
Ian
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FollowupID: 557541

Follow Up By: Nomadic Navara - Thursday, Mar 27, 2008 at 11:08

Thursday, Mar 27, 2008 at 11:08
"The Mains Charger I would only connect to the battery when plugged in to 240 volt. Some chargers could draw a small current from the battery if they are not connected to 240 volts."

All caravan manufacturers install the battery chargers connected directly to the battery, not through an isolation switch. I am yet to here of anyone having problems with flat batteries due to any charger being left connected to the battery - be it a mains charger, 12V battery booster or solar regulator.

PeterD
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FollowupID: 560912

Reply By: Mike Harding - Tuesday, Mar 11, 2008 at 18:05

Tuesday, Mar 11, 2008 at 18:05
Why do you wish to connect your car (if that is the vehicle alternator you mean?) to batteries intended to supply a house?

Mike Harding
AnswerID: 292130

Follow Up By: Axel [ the real one ] - Tuesday, Mar 11, 2008 at 18:28

Tuesday, Mar 11, 2008 at 18:28
House batts as per : c/van- camper trailer perhaps ?? rather than bricks and mortar "house"........
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FollowupID: 557486

Follow Up By: Dunaruna - Tuesday, Mar 11, 2008 at 20:37

Tuesday, Mar 11, 2008 at 20:37
LOL! How do I insert a smiley face?
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FollowupID: 557522

Follow Up By: Mike Harding - Tuesday, Mar 11, 2008 at 20:56

Tuesday, Mar 11, 2008 at 20:56
>LOL! How do I insert a smiley face?

On this forum you cannot (and I'm happy with that) a traditional internet ASCII ":)" is the closest one can get.

Over the 34 years I have been involved in electronic engineering design one of the things I have learned is that one needs to be clear and specific when asking questions otherwise one tends to receive the wrong answers.

I long ago learned than prescience in engineering does not exist.

When things are not clearly stated... ask... do not guess.

Mike Harding
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FollowupID: 557535

Follow Up By: Member - Noldi (WA) - Tuesday, Mar 11, 2008 at 21:06

Tuesday, Mar 11, 2008 at 21:06
Sorry Mike,
I assumed (yes I know) that it was a common term

Rgds
Ian
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FollowupID: 557543

Follow Up By: Dunaruna - Tuesday, Mar 11, 2008 at 21:07

Tuesday, Mar 11, 2008 at 21:07
No argument there, Mike. I just gotta a mental picture of a caravan made of bricks - put a smile on my dial.
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FollowupID: 557544

Follow Up By: Mike Harding - Tuesday, Mar 11, 2008 at 21:19

Tuesday, Mar 11, 2008 at 21:19
Hi Ian

So we're talking batteries in a caravan being charged from the three sources you mentioned?

Well... I don't really agree with MikeR on this occasion - what he states will be technically correct in some (many?) circumstances but I think it's leaving too much to chance. As Sir Humphrey said "I foresee all kinds of unforeseeable problems!" :)

I would, ideally, use a 2 pole, 3 way switch to do what you suggest (there is probably an expensive electronic solution but the switch will work OK - and be $X00.00 cheaper). If you cannot readily find such a switch (and outside the tech area it may be a problem) you could use three separate 2 pole switches and _ENSURE_ you _NEVER_ close two of them at the same time, which is not a hard thing to do :)

Mike Harding
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FollowupID: 557552

Follow Up By: Member - Mike DID - Tuesday, Mar 11, 2008 at 22:44

Tuesday, Mar 11, 2008 at 22:44
. . . and that's the great thing about this Forum.

You get to hear many different views on a topic.
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FollowupID: 557579

Follow Up By: Nomadic Navara - Thursday, Mar 27, 2008 at 11:34

Thursday, Mar 27, 2008 at 11:34
Regarding FollowUp 6 - All modern battery chargers (quality ones) are constructed so that there is no significant back drain from the battery when they are switched off. This means that you can have any number of them connected to your battery (except if you have one of the old style shunt solar regulators - if you can still find one.)

All chargers connected to a battery will have slightly different charging voltages. When one exceeds the operating voltage of another, the one with the lower voltage one will simply cease supplying current to the battery - its regulator will simply cut its output back to the point where nothing flows through it.

I have a Durst battery charger and a Morningstar ProStar controller both permanently connected to my van battery. On the previous van I had a Twin Charger and a mains battery charger connected to my battery. There has been no problem with battery discharge by the chargers on either van.

PeterD
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FollowupID: 560915

Reply By: Member - Noldi (WA) - Wednesday, Mar 12, 2008 at 08:24

Wednesday, Mar 12, 2008 at 08:24
Thanks all you have given me food for thought, I think a little more investigation is called for

Rgds
Ian
AnswerID: 292255

Reply By: Nomadic Navara - Thursday, Mar 27, 2008 at 12:00

Thursday, Mar 27, 2008 at 12:00
Ian

If your solar charging is effective I would suggest you do not attempt to connect your vehicle alternator to your house battery.

With your vehicle and house systems interconnected, the vehicles alternator will be the system voltage controller. With your motor at working temperature, the alternator output will be less than 14V. However, without the systems interconnected the solar regulator will charge your battery with a voltage in excess of 14V. The higher the voltage across your battery, the higher the battery charging current will be.

The reason for reduced charging with the systems interconnected. - The electrical load on the vehicle system will be greater than the solar system can supply. When the voltage of the solar system is potentially higher than the vehicle (ie will be higher if the two systems are separated) - current will flow towards the vehicle's electrical system. This current flow to the vehicle's system will attempt to raise the system voltage of the whole system - the result of this is the alternator regulator will cut back the the alternator's output to compensate and bring the voltage back to its designed voltage. Thus the solar panel will be contributing to the current requirements of your vehicle.

There is no sense in using your solar system to supplement the vehicles alternator.

PeterD
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AnswerID: 294984

Follow Up By: oldtrack123 - Thursday, Mar 27, 2008 at 23:43

Thursday, Mar 27, 2008 at 23:43
Hi
The key point is IF YOUR SOLAR POWER IS SUFFICIENT to run your fridg[especialy 3way 12v] etc & fullly charge aux bats[especially if low ]while driving ,if it not then the problem of feeding engine elects will not or rarely occur, & you may need the alternator to supplement solar.
You need to look at this carefully to decide which is best for you.
You could fit a votmeter & a paralelling relay with switch in coil circuit to manually switch of relay when you see voltmeter drop back or stay around 13.8 v
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FollowupID: 561107

Reply By: Member - Noldi (WA) - Friday, Mar 28, 2008 at 17:33

Friday, Mar 28, 2008 at 17:33
Thanks everyone, just goes to show how complicated these simple solutions can be.

I have no idea if this simplified pic will work but have decided to try this. I know there is a chance of forgetting to switch on and off but everything is a compramise when you have a budget

Image Could Not Be Found
AnswerID: 295271

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