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sidrgurney 
Member - Posts: 4
Member spacespace
Joined: November 12, 2010
Location: Florida, United States
Posted: November 14, 2010 at 5:18 AM / IP Logged  
Greetings! 
PROJECT: Install a wiring system to periodically connect a secondary marine deep-cycle battery & power inverter at rear of vehicle strictly when parked for tailgating & camping needs.
CAR: factory stock 2010 Honda Odyssey EX-L.
POWER INVERTER: PowerToGo PPI 2000 Watts Continuous / 4500 Watts High Surge DC to AC Inverter.
LOAD:  Coffee maker, small microwave, minimal lighting, small TV - DVD player, not all at same time.
DETAILS: I'm thinking the 1st part of wiring system will begin at the car battery's positive terminal, immediately connect to a fuse, then a battery isolator and then run appx. 10 - 12 feet beneath and to the rear of the car to an Anderson SB connector.  The 2nd part will be continue from the SB connector to the marine deep-cycle battery and on to the inverter.  Hardwire connection between deep-cycle battery & inverter is appx. 3 feet. 
QUESTIONS: What gauge wire, size of fuse, battery isolator and SB connector should be used?  Since I have 2 batteries, do I need more that one fuse and if so, where?  Should I run the negative wire from the car-side SB connector back to the car battery or ground to the metal frame or both?  Do you have any other recommendations?  Thanks very much!      
You just don't know what Indy means ....
howie ll 
Pot Metal - Posts: 16,466
Pot Metal spacespace
Joined: January 09, 2007
Location: United Kingdom
Posted: November 14, 2010 at 7:56 AM / IP Logged  
PM Oldspark with this, he's the guru on this topic.
sidrgurney 
Member - Posts: 4
Member spacespace
Joined: November 12, 2010
Location: Florida, United States
Posted: November 14, 2010 at 12:14 PM / IP Logged  
OK, Thanks! 
You just don't know what Indy means ....
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: November 14, 2010 at 8:07 PM / IP Logged  
Dang! I sent a LONG PM before reading this.
But I gotta go for now...
But now I'm back, so to augment my PM:
2,000 Watts is about 200A.
The 2nd battery will take probably 2A minimum when fully charged (float current).
How much it takes depends on how discharged it is, its type, size, & charging voltage. As per my PM, my 38AH AGM initially takes 40-50A after cranking. This reduces to under 10A withing 60 seconds.
Sizing depends on your max load demand plus your average battery demand plus a bit extra.
You may not have to size for your peak battery current as fuses & breakers have a reaction time - ie, they may tolerate 110% rated load for 15 minutes, 50% overload for a few minutes.
Hence I might chose 150A cabling etc with my 38AH AGM if the inverter uses 120A or less (ie, ~1200W output). This means 120A plus say 60A peak battery (total 180A) dropping to under (say) 140A in under 1 minute.
You need to decide your maximum load for cable etc sizing, but then add your average or peak battery recharge current.
The total figure (if too high) can be moderated by the real average consumption - eg, coffee maker 1,000W = 100A but only for 30 minutes every few hours. (Not that you might use the coffee maker whilst mobile, but you may have the engine running for battery charging.)
Or maybe decide to run such high loads opff the 2nd battery only. Hence when charging, you recharge the battery only - not the extra 100A for the coffee maker.
Fuse-wise, you need a fuse at each end near the battery.
You may prefer self resetting circuit breakers if peak current is likely to blow fuses and you do not have any fuse alarms.
The ground should be via chassis - unless it's a trailer etc else semi-detached (maybe a ute tray etc).
My PM mentioned my usual charge-lamp recommendation rather than the inferior or more expensive "smart isolators" that use voltage sensing. (As well as "priority charging" rubbish!)
I also provided sample calculations for inter-battery voltage drops though I did not mention that protection and connectors contribute to the total resistance (except for zero-resistance circuit breakers).
sidrgurney 
Member - Posts: 4
Member spacespace
Joined: November 12, 2010
Location: Florida, United States
Posted: November 15, 2010 at 9:18 AM / IP Logged  
Thanks very much, Oldspark!  I appreciate your advice!  You gave me several things to think about to do this right.  THX! 
You just don't know what Indy means ....
sidrgurney 
Member - Posts: 4
Member spacespace
Joined: November 12, 2010
Location: Florida, United States
Posted: November 16, 2010 at 7:35 PM / IP Logged  
I found this edition of Honda's Odyssey has a factory-stock alternator rated at 130 Amps.
You just don't know what Indy means ....
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: November 16, 2010 at 10:41 PM / IP Logged  
Good info. That's a reasonable size...
Keep in mind that its 130A is probably at a highish RPM - ie, not at idle to 3,000 RPM.
130A @ 13.8V implies ~1800W (or ~1870 at 14.4V) as a maximum load without discharging the battery.   
It would probably handle a 1000W continuous load assuming normal driving (not too much stop-start at idle).
But that includes engine and lights and stereo & & & ....
Yet again the best "monitor" is a voltmeter across the battery for SOC (State Of Charge) of the battery.
But remember that SOC is an OPEN circuit measurement (no load; no charging) with surface charge removed. (Eg ~11.4V is probably 100% discharged (and damaged!); ~12.7V is fully charged; and anything up up to ~13.7V with surface charge.)
And even if fully discharged, an alternator will usually bring the voltage up to normal (somewhere between 13.8 & 14.4V).
And of course there are 2 batteries (ie, 2 voltmeters, or a battery selector switch?).
If you mentioned the alternator rating to help size the interconnect - it doesn't.
It is (1) the equipment load (meaning accessories, attachments etc) PLUS (2) the battery recharging load that determines that.
If that figure gets too high (for economical or reasonable design), then an average figure could be used rounded up to the next relay/fuse size.
EG - if coffee maker is max load and is 1,000W, and battery might take 70A if reasonable discharged...
1000W/13.8V = 72A + 70A battery = 142A = (say) 150A relay/isolator/fuse/cable. Maybe 200A isolator; 300A cable and 150A fuse in practice.
But if its 1000W @ 12V (not charging; and the coffee maker is a constant power load), then 1000W/12V = 83A compared to its 72A @ 13.8V.
But the battery won't be charging, hence 83A total, not (72A+70A) nor (83A+70A). Cool!
Let's say a 150A relay etc is too expensive.
Or we realise that is overkill. IE - coffee whilst stationary (not charging, hence 80-90A) and the biggest "in motion" load is DVD/TV at say 200W - ie about 20A.
Hence we decide a 100A relay/isolator is adequate.
100A handles the 1000W "constant power" coffee maker. (1000W/100A = 10V; ie, handles the 100A that the 1000W coffee maker takes if it was getting 10V (maybe due to a 1V drop between it and the front 11.0V battery).
100A also handles the 20A DVD/TV and the 70A "maximum" rear battery recharge current (if using whilst charging).
If the 100A is exceeded, then the interconnect fuses will blow - maybe never for 110A, maybe after 15 minutes for 120A, and maybe after 60 seconds at 150A etc.
That's annoying if it's a temporary problem. (EG - excessively discharge battery is taking 120A, or we started the engine whilst running the coffee maker (142A etc).)
That's when either a fuse-blown alarm is handy, else self-resetting circuit breakers. (I use the latter. Assuming the load is reasonably less than the circuit breaker rating, in practice the battery will usually charge more than discharge, hence battery recharge current decreases each time the breakers reconnect. Just make sure breakers fail properly rather than melt or explode!)
But that'll do for now. The above gives some considerations or situations - though in some cases no rear battery (to contribute power) is considered.
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: November 18, 2010 at 2:34 AM / IP Logged  
And now - with thanks to wizMaster izu - a new version of the infamous Ultimate Intelligence Battery Isolator (For Those That Have a Charge Light) diagram....
power inverter -- posted image.
Yes - it's the same old drawing, but with the Aux Battery and Isolator moved to the LHS.
For those that are still confused and think it is still too complex, try the circuit below instead.
power inverter -- posted image.
FYI sidrgurney - I'm not having a go at you... Rather I am reflecting those that think the upper fig is too complex yet are happy with the lower fig, or alternative products that show similar detail.
In fact - come to think of it - I don't think I'm reflecting anyone on the12volt!    
Most here might realise that the lower is the simple marketing version for the simply-doers, whilst the upper is for the wanna-understanders.
The top fig is a functional diagram that shows how it works with "normal" car wiring.
A voltage sensing battery isolator would be the same layout but with the relay (#86) controlled by an internal voltage switch that gets its voltage from the relay's heavy input #30 (as opposed to #86 simply using the alternator's D+ or L chargeLamp signal).

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