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dobryan
Samba Member
Joined: March 24, 2006
Posts: 16505
Location: Brookeville, MD
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 Posted: Fri Nov 29, 2019 5:39 pm Post subject: Relay to combine starter and aux batteries only when running |
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Full disclosure: I did a search and think I have seen a similar topic but my search foo is weak today.
I have finally come to the realization that I do not want a combiner like a Yandina or other to link my house and staring battery whenever a charge source is present on either. I want my solar system and shore charger (Iota30) to only charge my house batteries, not the starting battery. The starting battery does not need to be in the system when those two devices are charging the house batteries. It is fine on its own. I DO want the alternator to be able to add charge to the house batteries when the engine is running.
Soooo... I know how to wire up a relay so that it kicks on when the bus is running. My question is basically two parts:
1) What is a properly rated relay to carry the charging load?
2) What size wire to run from the alternator to the relay to properly limit the charge current to a reasonable amount. I will have two 80Ah AGM house batteries and when deeply discharged they could draw a large current. I know the Yandina uses only a 10g wire to limit the charge current. Is this something I should emulate?
Paging crazyvwbusman and other electric gurus. 
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Dave O
'87 Westy w/ 2002 Subaru EJ25 and Peloquin TBD
"To travel hopefully is a better thing than to arrive." Robert Louis Stevenson
MD>Canada>AK>WA>OR>CA>AZ>UT>WY>SD
https://www.thesamba.com/vw/forum/viewtopic.php?t=620646
Building a bus for travel in Europe (euroBus)
https://www.thesamba.com/vw/forum/viewtopic.php?t=695371
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?Waldo?
Samba Member
Joined: February 22, 2006
Posts: 9752
Location: Where?
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| Posted: Fri Nov 29, 2019 5:48 pm Post subject: Re: Relay to combine starter and aux batteries only when running |
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It's a van, not a bus. There is no user named 'crazyvwbusman'.  |
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beach_creature
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Joined: April 11, 2014
Posts: 532
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| Posted: Fri Nov 29, 2019 5:50 pm Post subject: Re: Relay to combine starter and aux batteries only when running |
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Do you have a set up currently that you are wanting to change? Or is this something that you will be building?
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84 Westy
1.9TD AAZ
5spd manual with Locking Peloquin TBD |
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crazyvwvanman
Samba Member
Joined: January 28, 2008
Posts: 9937
Location: Orbiting San Diego
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| Posted: Fri Nov 29, 2019 6:01 pm Post subject: Re: Relay to combine starter and aux batteries only when running |
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The suitable relay size and wiring size depend on the rest of the configuration.
How big is the battery, where is the battery, what connection point is to be used to get alternator power while the engine is running.
There are 2 simple ways to control the relay.
1. use the blue wire circuit like vw does, assuming a Bosch alternator
2. use the "X" circuit to control the relay
Both of these will disconnect the aux battery from the starting battery when the key is off and during starting.
I would most times use a standard 4 pin 70 amp relay, and the rest of the time use a heavier 100 amp relay. For blue wire relay control the 70 amp is probably better assuming the load capacity is suitable.
Maybe more later if I find some time.
Mark |
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dobryan
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Joined: March 24, 2006
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Location: Brookeville, MD
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fxr
Samba Member
Joined: December 07, 2014
Posts: 2325
Location: Bay area CA
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| Posted: Fri Nov 29, 2019 7:19 pm Post subject: Re: Relay to combine starter and aux batteries only when running |
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I have a similar set-up to what you want. I use a GoWesty relay (just because I had it already) controlled by the Westy fridge relay. This in turn is now controlled by the 'X' circuit, as I have a Subie conversion, and the blue wire doesn't cut it.
You could use any generic 70A (or higher rated) relay controlled directly by the 'X' circuit - and 10 gauge wire will be quite adequate.
My solar (and shore power if ever I use it) only charges my house batteries.
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Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300 |
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MarkWard
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Joined: February 09, 2005
Posts: 17155
Location: Retired South Florida
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| Posted: Sat Nov 30, 2019 5:22 am Post subject: Re: Relay to combine starter and aux batteries only when running |
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I am using a manual A B battery switch from the marine industry. The switch can isolate the batteries when stopped. I can also disconnect both batteries for my built in charger that can charge independently 3 batteries. I used heavy cable between the switch and the starter solenoid so I can start and run the engine off of either battery or combined. This setup works fine and saved our butts when we had to evacuate and the starting battery happened to have failed. Takes a few brain cells to remember to operate it.
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Butcher
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Joined: December 05, 2015
Posts: 1285
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| Posted: Sat Nov 30, 2019 6:42 am Post subject: Re: Relay to combine starter and aux batteries only when running |
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| If the batteries are only going to be charged from the alternator, I do not see a need to have a 70A relay. Would it hurt? No, but it's certainly more than that circuit would ever use. |
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Gnarlodious 
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Joined: September 28, 2013
Posts: 2323
Location: Adobe Jungle USA
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| Posted: Sat Nov 30, 2019 8:37 am Post subject: Re: Relay to combine starter and aux batteries only when running |
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You might want to read my solution to combine two different kinds of batteries using a programmable voltage switch:
https://www.thesamba.com/vw/forum/viewtopic.php?t=650913 (sorry my video is no longer online)
The system is completely automated and has run without trouble for years. The controller is this device:
https://www.ebay.com/itm/171518613069
It means you can use a generic relay and have complete control over all variables.
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fxr
Samba Member
Joined: December 07, 2014
Posts: 2325
Location: Bay area CA
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| Posted: Sat Nov 30, 2019 9:08 am Post subject: Re: Relay to combine starter and aux batteries only when running |
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| Butcher wrote: |
| If the batteries are only going to be charged from the alternator, I do not see a need to have a 70A relay. Would it hurt? No, but it's certainly more than that circuit would ever use. |
Very true - but 30A continuous for a while is quite probable with a severely discharged high capacity battery. I always choose components that can handle at least double their expected 'stress', whether that be temperature, voltage or current.
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Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300 |
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dobryan
Samba Member
Joined: March 24, 2006
Posts: 16505
Location: Brookeville, MD
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| Posted: Sat Nov 30, 2019 9:20 am Post subject: Re: Relay to combine starter and aux batteries only when running |
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Just to clarify:
I intend to have an AGM starting battery and AGM house batteries.
I have solar to charge the house batteries while camping with no shore power (no 110V outlet nearby). I do not want to also charge the starting battery then.
I have an Iota30 for charging the house batteries and as a power supply when there is shore power available (110V outlet nearby). I do not want to also charge the starting battery then.
While the engine is running I want to charge the starting battery and house batteries from the alternator. This is the only time I want this to occur. This needs to occur without my intervention, I have CRS.
So it looks like a 10gauge wire (fused both ends) directly from the alternator to a relay triggered by the X circuit is all I need to do.
Looking at this relay.
https://www.amazon.com/Ehdis-Truck-Normally-Socket...amp;sr=8-3
Anyone have anything they see I am doing wrong?
Thanks!
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Dave O
'87 Westy w/ 2002 Subaru EJ25 and Peloquin TBD
"To travel hopefully is a better thing than to arrive." Robert Louis Stevenson
MD>Canada>AK>WA>OR>CA>AZ>UT>WY>SD
https://www.thesamba.com/vw/forum/viewtopic.php?t=620646
Building a bus for travel in Europe (euroBus)
https://www.thesamba.com/vw/forum/viewtopic.php?t=695371
The Western Syncro build
https://www.thesamba.com/vw/forum/viewtopic.php?t=746794 |
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crazyvwvanman
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Joined: January 28, 2008
Posts: 9937
Location: Orbiting San Diego
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| Posted: Sat Nov 30, 2019 9:30 am Post subject: Re: Relay to combine starter and aux batteries only when running |
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Along with battery size it depends on the alternator voltage set point along the gauge and length of the wiring.
My ammeter reading indicated 60+ amps many times with my 125ah deep cycle.
It would be that high for a minute or two after the engine was running and taper down pretty quickly to under 30a.
Alternator was set for 14.5v, wiring was short marine #6. I later changed the wiring to smaller and longer to lower the peak amps some.
Charge control was through an industry standard 100a relay.
Long life silver plated contacts, 400a inrush, get the real thing not a lookalike knockoff.
https://www.mouser.com/ProductDetail/802-120-902
https://www.mouser.com/datasheet/2/459/R-4002web-335055.pdf
Mark |
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dobryan
Samba Member
Joined: March 24, 2006
Posts: 16505
Location: Brookeville, MD
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| Posted: Sat Nov 30, 2019 9:39 am Post subject: Re: Relay to combine starter and aux batteries only when running |
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| crazyvwvanman wrote: |
Along with battery size it depends on the alternator voltage set point along the gauge and length of the wiring.
My ammeter reading indicated 60+ amps many times with my 125ah deep cycle.
It would be that high for a minute or two after the engine was running and taper down pretty quickly to under 30a.
Alternator was set for 14.5v, wiring was short marine #6. I later changed the wiring to smaller and longer to lower the peak amps some.
Charge control was through an industry standard 100a relay.
Long life silver plated contacts, 400a inrush, get the real thing not a lookalike knockoff.
https://www.mouser.com/ProductDetail/802-120-902
https://www.mouser.com/datasheet/2/459/R-4002web-335055.pdf
Mark |
Thank you!
What wire size/length do you recommend? I am not interested in taxing the alternator so lowering the peak amps would be the goal. I do have an adjustable regulator so I can turn up the voltage if I decide it is warranted.
I will have two 80ah AGM batteries as the house battery bank.
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Dave O
'87 Westy w/ 2002 Subaru EJ25 and Peloquin TBD
"To travel hopefully is a better thing than to arrive." Robert Louis Stevenson
MD>Canada>AK>WA>OR>CA>AZ>UT>WY>SD
https://www.thesamba.com/vw/forum/viewtopic.php?t=620646
Building a bus for travel in Europe (euroBus)
https://www.thesamba.com/vw/forum/viewtopic.php?t=695371
The Western Syncro build
https://www.thesamba.com/vw/forum/viewtopic.php?t=746794 |
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crazyvwvanman
Samba Member
Joined: January 28, 2008
Posts: 9937
Location: Orbiting San Diego
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| Posted: Sat Nov 30, 2019 9:50 am Post subject: Re: Relay to combine starter and aux batteries only when running |
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I hate to be too specific since people take pieces out of context and apply them inappropriately. I would test the peak amp draw with your specific batteries, drained down by 30% first, and connected to the actual alternator setup that will be in use. I generally like marine grade #8 to the aux since it can briefly carry the full alternator output with a stock alternator. Since you plan to connect at the starter keep in mind that the wire from the alternator to the starter is also a factor in determining the peak current. Resist making that section of wire too large of a gauge, marine #6 max for me.
My comments above are meant to apply only to use of a properly controlled aux battery relay since other connection methods such as switches or ACR may result in the aux battery supplying higher current during starting than the mentioned wiring should be subjected to.
Mark
Last edited by crazyvwvanman on Sat Nov 30, 2019 9:55 am; edited 1 time in total |
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dobryan
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Joined: March 24, 2006
Posts: 16505
Location: Brookeville, MD
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| Posted: Sat Nov 30, 2019 9:54 am Post subject: Re: Relay to combine starter and aux batteries only when running |
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| crazyvwvanman wrote: |
I would test the peak amp draw with your specific batteries, drained down by 30% first, and connected to the actual alternator setup that will be in use. I generally like marine grade #8 to the aux since it can briefly carry the full alternator output with a stock alternator. Since you plan to connect at the starter keep in mind that the wire from the alternator to the starter is also a factor in determining the peak current. Resist making that section of wire too large of a gauge, marine #6 max for me.
Mark |
I've decided to go directly from the alternator so as not to tax the alt to starter wiring.
Looks like marine grade 8 gauge at about 6 feet would be the result. Sound correct?
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Dave O
'87 Westy w/ 2002 Subaru EJ25 and Peloquin TBD
"To travel hopefully is a better thing than to arrive." Robert Louis Stevenson
MD>Canada>AK>WA>OR>CA>AZ>UT>WY>SD
https://www.thesamba.com/vw/forum/viewtopic.php?t=620646
Building a bus for travel in Europe (euroBus)
https://www.thesamba.com/vw/forum/viewtopic.php?t=695371
The Western Syncro build
https://www.thesamba.com/vw/forum/viewtopic.php?t=746794 |
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Gnarlodious
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Joined: September 28, 2013
Posts: 2323
Location: Adobe Jungle USA
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| Posted: Sat Nov 30, 2019 9:28 pm Post subject: Re: Relay to combine starter and aux batteries only when running |
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I would caution against using an IOTA charger on AGM batteries. I used one for several years and had a chronically undercharged battery (Odyssey) with reduced capacity and disappointing battery life (talking about a $250 battery every 3 years). After much arguing with IOTA technicians I sent it in and they sent it back saying it was working as designed. However it still could not hit the 14.8 volts recommended to fully charge the Odyssey.
I finally dumped the IOTA and got a ProMariner Prosport, which manages AGM just fine. Have not had a battery problem since.
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dobryan
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dobryan
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dobryan
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shagginwagon83
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| Posted: Sun Dec 01, 2019 8:20 am Post subject: Re: Relay to combine starter and aux batteries only when running |
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I'm leaning towards the IOTA also now.
For what its worth, I'm using a relay to control the ground of my 'SI_ACR' relay. Kinda defeats the whole purpose of an automatic relay - so I'd recommend like a 70amp relay mentioned above.
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Brandon
"Jo Ann" - '83.5 Westfalia EJ22e w/Peloquin
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