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Dual battery installation using 70A battery relay 77 camper
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larrydeville
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PostPosted: Wed Jun 05, 2013 9:11 pm    Post subject: Dual battery installation using 70A battery relay 77 camper Reply with quote

I have read that the solid state battery isolators have a bit of voltage drop. I go way back in the sierras and fear a dead battery so Im setting up a second battery for water pump,interior lights and stereo. The second battery is going to be isolated with a 70A ignition key on switched relay to protect the engine battery from accidental discharge. My question is....if I have run the aux battery down...when I turn the key to on/start position Im in effect jumping the main battery with a dead battery. I could put a switch in series with the ign on pwr to keep the relay off during start if the aux battery is dead but then is there any danger of frying my regulator when I turn the aux bat relay on? Im worried about dumping a big load all at once on the alternator might not be good for it. Thx...Larry
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SGKent Premium Member
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PostPosted: Wed Jun 05, 2013 9:14 pm    Post subject: Reply with quote

buy a good battery isolator that is designed to do the thinking for you.
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poptop tom
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PostPosted: Thu Jun 06, 2013 4:49 am    Post subject: Reply with quote

This is what I used between my batteries for isolation.

http://www.westmarine.com/webapp/wcs/stores/servle...sNum=50547
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Vince Waldon
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PostPosted: Thu Jun 06, 2013 8:42 am    Post subject: Reply with quote

You're not wrong... there is a bit of a voltage drop when you use a battery isolator... and it's to both batteries unfortunately... but in the overall scheme of things the alternator is still able to provide more than enough voltage to charge the batteries properly.

And... the one time you or someone else forgets to defeat your 70A charge relay as you start your bus hundreds of amps from your second battery will flow thru the relay on their way to the starter and the magic smoke may be released. Smile

Battery isolator = proven and fool-proof way to accomplish what you're after.
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aeromech
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PostPosted: Thu Jun 06, 2013 9:41 am    Post subject: Reply with quote

What Poptop Tom said

I've installed several Blue Sea "add a battery" kits into VW buses with good results. The way it works is so simple. Turn the battery switch ON and leave it there. With the engine not running the batteries are separated. Run all of your accessories off the AUX battery for camping. The START battery is isolated with no loads. When you start the engine the starter cranks from the START battery. Once the ACR (automatic charging relay) senses 14 volts from the alternator about 5 seconds later it closes and connects both batteries to the alternator for charging. If you ever have an issue with a low or dead start battery you can move the switch to COMBINE and use both batteries to start the engine.

Image may have been reduced in size. Click image to view fullscreen.


One last comment: I found that the ACR has a constant small drain of a few milliamps. If the bus is left for several days without charging this can cause a low battery condition. Because of that I now wire in a cheap relay that removes the ground from the ACR when the key is off. That solved that issue.
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larrydeville
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PostPosted: Thu Jun 06, 2013 10:23 pm    Post subject: Dual battery installation using 70A battery relay 77 camper Reply with quote

Thank you for the help.....the photo of the engine compartment is very nice.....Larry.
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a-marshal
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PostPosted: Fri Jun 07, 2013 5:18 am    Post subject: Reply with quote

aeromech wrote:
I've installed several Blue Sea "add a battery" kits into VW buses with good results. ...snip ... I found that the ACR has a constant small drain of a few milliamps. If the bus is left for several days without charging this can cause a low battery condition. Because of that I now wire in a cheap relay that removes the ground from the ACR when the key is off. That solved that issue.


I've had they same issue with my BlueSea though it only comes up during winter storage. The relay is a nice solution, what was/ is the type and rating of the relay (I assume normally open) and which wire do you tap to power it?
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aeromech
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PostPosted: Fri Jun 07, 2013 7:52 am    Post subject: Reply with quote

a-marshal wrote:
aeromech wrote:
I've installed several Blue Sea "add a battery" kits into VW buses with good results. ...snip ... I found that the ACR has a constant small drain of a few milliamps. If the bus is left for several days without charging this can cause a low battery condition. Because of that I now wire in a cheap relay that removes the ground from the ACR when the key is off. That solved that issue.


I've had they same issue with my BlueSea though it only comes up during winter storage. The relay is a nice solution, what was/ is the type and rating of the relay (I assume normally open) and which wire do you tap to power it?


I take a very common relay that's available at all FLAPS and costs about $5. The ACR needs to be grounded to work so I just use the relay as a switch for this ground. The relay is powered from the + side of the coil so when you turn the key on the relay closes and now the ACR is grounded. The rating of the relay is 30 amp I think but anything will work.

Image may have been reduced in size. Click image to view fullscreen.

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luapekralc
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PostPosted: Mon Apr 27, 2015 3:00 pm    Post subject: Bus won't turn off with Aux Battery connected Reply with quote

Hi,

I've installed a second battery (wiring was already there). The circuit looks exactly like this diagramme: http://tinyurl.com/lf3xqb2

So the relay (I've tried three different ones with the same result) is connected to the Blue Regulator feed so that it is energized only when the engine is running pin85 to regulator, pin86 to ground). This connects the positive side of the main battery (pin87) to the auxilliary battery on pin 30/51.

Testing shows that when the ignition is OFF, there is power only on pin 30 because it is connected to the Aux Battery. With the ignition key ON there is power now on pin 87 and pin 30, but they are not connected because there is no power on pin 85. With the ignition Running there is power on Pin 85, 87, 30 and pin 87 and 30 are connected.

Here's the problem, when I turn the ignition OFF the engine continues to run, there is power to all three powered pins. The engine shuts off as expected only if I pull either the Regulator feed (Pin 86) or the main power feed (pin 87).

Additional info, at this point there is nothing connected to the Aux Battery, just the relay and the ground. Wanted to get it charging before linking in accessories.

Would appreciate any suggestions.
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telford dorr
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PostPosted: Tue Apr 28, 2015 9:10 am    Post subject: Reply with quote

Any chance you could post a link to a bigger version of the schematic? The one already posted is too small to see (even when zoomed in on...)

Looks like, because of the way you wired it, once the relay pulls in, it connects the aux battery to the downstream side of the ignition switch, powering it continually. Thus, you can't turn it off. To fix, move the #87 wire to the upstream side of the ignition switch, or better yet, to the '+' terminal on the main battery.

This change will also take the aux battery charging load off of the ignition switch, which could otherwise easily overload it.
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Bleyseng
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PostPosted: Tue Apr 28, 2015 11:28 am    Post subject: Re: Bus won't turn off with Aux Battery connected Reply with quote

luapekralc wrote:
Hi,

I've installed a second battery (wiring was already there). The circuit looks exactly like this diagramme: http://tinyurl.com/lf3xqb2

So the relay (I've tried three different ones with the same result) is connected to the Blue Regulator feed so that it is energized only when the engine is running pin85 to regulator, pin86 to ground). This connects the positive side of the main battery (pin87) to the auxilliary battery on pin 30/51.

Testing shows that when the ignition is OFF, there is power only on pin 30 because it is connected to the Aux Battery. With the ignition key ON there is power now on pin 87 and pin 30, but they are not connected because there is no power on pin 85. With the ignition Running there is power on Pin 85, 87, 30 and pin 87 and 30 are connected.

Here's the problem, when I turn the ignition OFF the engine continues to run, there is power to all three powered pins. The engine shuts off as expected only if I pull either the Regulator feed (Pin 86) or the main power feed (pin 87).

Additional info, at this point there is nothing connected to the Aux Battery, just the relay and the ground. Wanted to get it charging before linking in accessories.

Would appreciate any suggestions.


Could you make that diagram smaller........
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