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Old 12-28-2010, 04:34 PM   #1 (permalink)
Meathead
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Bed-Mounted Inverter and Aux. Battery

I'm planning to mount a power inverter in the bed of my truck, and am interested in advice from the resident auxiliary electric/electronic gurus about how to go about doing so - specifically, how to wire what to where, etc.

I've imagined an auxiliary battery, also mounted in the bed, wired to charge off the alternator just as the two OEM batteries do, but isolated so as to only provide power to the inverter. I'm curious, though, how to go about acheiving the charge from the alternator - what gauge wires, etc. Also, I've seen battery isolators for just such applications, but would appreciate any advice anyone may have (particularly from personal experience) with any particular model/brand of isolator, and exactly how to wire it so the inverter will draw from it, but not be permitted to draw down the OEM batteries.

If it's required info, the inverter to be installed is a Tripp-Lite Model PV1250FC.

Thank you in advance...
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Old 12-28-2010, 04:52 PM   #2 (permalink)
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I have the exact same inverter on my fifth wheel. It's good but I've had issues getting the full rated surge watts out of it to start some challenging loads like my air compressor.

Anyhow, it draws about 125 amps when it's running flat out. You will need a good bank of batteries (at least 2 deep cycles) to sustain it running under heavy load for any period of time without the engine running.

You will also need a heavy duty battery isolator to avoid the inverter drawing down your starting batteries when it's running without the truck running.

As for the gauge of wiring from the alternator to the battery bank? BIG. If you want the alternator to be able to effectively charge the bank when it's been drawn deeply down you want as much amperage as possible to reach the bank..and given the distance from the battery bank in your bed to the alternator I'd be reluctant to go much below 2 gauge myself...others may recommend 0 gauge.

Yeah, you can go with a lower gauge cable to save money but if you're only getting 5 or 10 amps to the back instead of everything your alternator can push you're going to find that secondary bank of batteries is dead most of the time...or they will take hours and hours to charge.
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Old 12-28-2010, 07:55 PM   #3 (permalink)
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I'd use 2/0 cable given the distance you'll be running to get from under the hood to the bed. Run a positive and negative, don't rely on the frame to handle the ground for that much current. I use a battery separator made by Blue Sea. It's been under the hood working great for over 7 years now. It has an in and out terminal, connect the in to the existing batter/alternator and connect the out to the second battery. When you start the truck and the voltage reaches the set point (adjustable) of around 13.2 volts it will connect the two together. When you turn off the engine, the voltage drops below that point and it will disconnect the batteries.
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Old 12-28-2010, 09:59 PM   #4 (permalink)
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We're already running inverters and this guy has the GM 3rd battery mount.

http://www.dieselplace.com/forum/sho....php?p=3474902

Here's what I'm running on most of them
power inverter

best power inverter for the $


And if you really wanna do some perusing, do an advanced search using "heymccall" as a username, and "inverter" as the search word.



Wagan slimline 1500 behind the seat


B-pillar outlets (I couldn't find black ones at the time)
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Old 12-29-2010, 08:32 AM   #5 (permalink)
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Quote:
Originally Posted by heymccall View Post
Here's what I'm running on most of them
power inverter
Hmmm...sooo, please excuse my electrical ignorance, but, is this "true sine" something I should be worried about?

This inverter will primarily be powering a laptop and an electric blanket for my dog, but may occasionally also power an cordless tool battery charger or other miscellaneous gadget. I don't anticipate ever running any power tools or anything that'd generate a large load.


Thanks to all three of you for your help.
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'07 CCSB LBZ Silverado Classic, 352,000 miles and counting - Nicktane - Kennedy Twin Lift Pumps & pickup - PPE Ported Fuel Rail Fitting - PPE Xcellerator Standard on 2 - ISSPRO EV2 boost, EGT, and fuel rail pressure on A-pillar; fuel pressure and (future) house battery voltage in Trippin' mount - Rotella T Syn. now on 45k OCI's w/ beautiful OA reports - Fumoto valve - BD manifold - MBRP dp, 4", muff, no cat - SPi PCV re-route (modified to actually work) - TransGo Jr, Transynd, deep Alli pan, deep filter, filter loc - Mag-Hytec diff cover, Mobil1 75w90 - Cognito UCA leveling, pitman and idler braces, sway bar end links, Rare Parts tie rods, Bilstein 5100's...and keys, 1" blocks, Firestone Ride-Rite air bags - Toyo OC ATs in 285/75-17-E on black H2s - Tekonsha P3 - Optima Red Tops - AMP steps - Recon smoked LED cab markers & mini tailgate bar - 5% tint everywhere - Leer cap, the "Williebago" - full LED interior...in red - Viper 5901 - RAM mount w/ iPad2 - Garmin Streetpilot 7200 - Garmin GPSmap 478
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Old 12-29-2010, 08:37 AM   #6 (permalink)
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Meathead,

You have some great info going so far, let me see if I can add a little.

1. There are two types of battery isolators. The old fashion isolation diodes and the new charge relays. You absolutely do not want an isolation diode. They will not work well with our alternators and create a voltage drop over the diode. Thus your auxiliary batteries will never charge.

What you want is a charge relay. There are a couple of choices; you can use an automatic one. These are common in the marine and RV world. An automatically relay senses that there is charging voltage available and connects the auxiliary battery so it charges. And then when there is no charging voltage it disconnects. Your second option is to use a relay that connects when the key is on. This how the GM aux. battery in the gassers works.

2. Cable size is going to take a fair amount of calculation.

First, since you are using an auxiliary battery setup you will be running charge cables to the battery(s). The size of these cables is going to be determined by alternator output and distance from the alternator. Just to throw around some numbers. Letís say you put the batteries and inverter at the front of the bed. You will be looking at about 15í between alternator and battery by the time you route the cable up and down and around. Your total cable distance is going to be 30í when you add the negative and positive cables together. With a 105 amp alternator you are looking at a 0 gauge cable to be safe. Now if you can get this distance down to 20 feet that size drops to only a #2 which is very possible if you look closely at how the cables will travel but it gives you an idea why the calculations are important. Here is a link to a wire size calculator that might help.

Wire size calculator

I will assume that your inverter will be located close to your battery and inverter cable size should be specified in the manual for your inverter and will be determined by the size of the inverter but these cables can easily be as big as 2/0 or even 4/0

Last make sure that you are fusing your cables and protecting them for damage. The last thing you want is a truck fire.

You can take a look at my install here if you would like.
Diesail power inverter install
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Old 12-29-2010, 08:49 AM   #7 (permalink)
Meathead
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Quote:
Originally Posted by diesail View Post
1. There are two types of battery isolators. The old fashion isolation diodes and the new charge relays. You absolutely do not want an isolation diode. They will not work well with our alternators and create a voltage drop over the diode. Thus your auxiliary batteries will never charge.

What you want is a charge relay. There are a couple of choices; you can use an automatic one. These are common in the marine and RV world. An automatically relay senses that there is charging voltage available and connects the auxiliary battery so it charges. And then when there is no charging voltage it disconnects. Your second option is to use a relay that connects when the key is on. This how the GM aux. battery in the gassers works.
That's great info, thanks. I've used a diode type isolator before (though I knew not wth I was doing...not unlike this project), and probably would have here as well had you not said something. Thanks.


Quote:
Originally Posted by diesail
2. Cable size is going to take a fair amount of calculation.

First, since you are using an auxiliary battery setup you will be running charge cables to the battery(s). The size of these cables is going to be determined by alternator output and distance from the alternator. Just to throw around some numbers. Letís say you put the batteries and inverter at the front of the bed. You will be looking at about 15í between alternator and battery by the time you route the cable up and down and around. Your total cable distance is going to be 30í when you add the negative and positive cables together. With a 105 amp alternator you are looking at a 0 gauge cable to be safe. Now if you can get this distance down to 20 feet that size drops to only a #2 which is very possible if you look closely at how the cables will travel but it gives you an idea why the calculations are important. Here is a link to a wire size calculator that might help.

Wire size calculator

I will assume that your inverter will be located close to your battery and inverter cable size should be specified in the manual for your inverter and will be determined by the size of the inverter but these cables can easily be as big as 2/0 or even 4/0

Last make sure that you are fusing your cables and protecting them for damage. The last thing you want is a truck fire.
I actually happen to have two 30' long 2/0 cables (actually slightly used welding leads) that I've thought I may be able to use for this. Is there any reason I shouldn't do that? Also (and again, please excuse my ignorance), can you suggest a way to make the connection of a 2/0 cable to the alternator?

The inverter will be, as you suggested, mounted at the front of the bed, the bottom of the inverter 6" or so above bed rail height. The auxiliary battery (or batteries - still have to make that decision), also as you suggested, will be mounted as close as is physically possible to the inverter.


Quote:
Originally Posted by diesail
You can take a look at my install here if you would like.
Diesail power inverter install
I'm studying it...
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Old 12-29-2010, 09:50 AM   #8 (permalink)
diesail
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Quote:
I actually happen to have two 30' long 2/0 cables (actually slightly used welding leads) that I've thought I may be able to use for this. Is there any reason I shouldn't do that? Also (and again, please excuse my ignorance), can you suggest a way to make the connection of a 2/0 cable to the alternator?
Welding cable is a great option. It is what I used on mine and use from most of my large battery cables as it is so much more flexible that "battery cable". It might be a bit large for your charge cable but it sure won’t hurt, other than it will make routing the cable a bit harder. To make your connection to the alternator you could use a smaller cable to a fuse or breaker then use the larger cable. If you look closely at my install you will see that the charge cable is actually fused on both ends, near the alternator and near the extra battery. This is something that I am a stickler about. A short in a cable can and will lead to a fire, so it is always best to fuse as close to the battery as possible. I chose to use a breaker on the alternator end, this gives me the freedom to disconnect the auxiliary system from the truck simply by turning off the breaker.

On my install for the charging circuit I did the following all in #2.

1) Positive as follow; Alternator –> breaker -> charge relay -> close to aux battery as possible-> fuse -> Battery
2) Negative ground upgrade from engine block to frame.
3) Auxiliary battery is grounded to frame via a 2/0 as part of the inverter connection.

In my circuit, since the frame is basically a really large cable its effect on circuit length is negligible, so my entire circuit length from alternator to battery and back is about 12’ if memory serves. This called for a #4 for a 105 amp alternator and I opted to go one size larger.

Also I am bit of a stickler when it comes to cable ends. I use nothing but closed end lugs sealed with adhesive lined heat shrink. This creates a completely sealed cable assembly and eliminates concerns over water wicking into the cable at the ends. A great source of cable ends is here http://shop.genuinedealz.com/

Last edited by diesail; 12-29-2010 at 09:51 AM.
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Old 12-29-2010, 10:13 AM   #9 (permalink)
Meathead
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Originally Posted by diesail View Post
...To make your connection to the alternator you could use a smaller cable to a fuse or breaker then use the larger cable. If you look closely at my install you will see that the charge cable is actually fused on both ends, near the alternator and near the extra battery. This is something that I am a stickler about. A short in a cable can and will lead to a fire, so it is always best to fuse as close to the battery as possible. I chose to use a breaker on the alternator end, this gives me the freedom to disconnect the auxiliary system from the truck simply by turning off the breaker...
That's all great, and exactly the kind of insight I was hoping to get. I may well bug the hell out of you before this is over, and I'll definitely owe you some kind of system design fee...

Do you have a manufacturer recommendation/source for the fuses and breakers? Any more info. on what to use there would be great.

Also, as I mentioned above, it's unlikely I'll be using this to power any large tools, and in the event I do, running the truck for the short period of time that I did would not be a problem. Given that, do you think a single auxiliary battery will be sufficient?

Lastly, did you catch the question above about the true sine issue? Is that something I should be concerned about?
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Old 12-29-2010, 10:15 AM   #10 (permalink)
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Quote:
Originally Posted by Meathead View Post
Hmmm...sooo, please excuse my electrical ignorance, but, is this "true sine" something I should be worried about?

This inverter will primarily be powering a laptop and an electric blanket for my dog, but may occasionally also power an cordless tool battery charger or other miscellaneous gadget. I don't anticipate ever running any power tools or anything that'd generate a large load.


Thanks to all three of you for your help.
The Tripp Lite model you quoted is pure sine, so no worries there. Most cheapie inverters are modified sine which can cause problems with some electronics such as battery chargers and electronics that need clean power - such as the laptop you mention.

They may run, but damage to the transformers can result...for example, I used a cheap 500w inverter to charge my Macbook on a road trip 4/5 years ago and discovered that the modified sine wave caused the transformer to heat up like crazy - symptomatic of it not being happy with the sine wave. With pure sine this doesn't happen, so it's often worth investing more in the inverter (if it's a long term keeper) versus a cheap one as it may save you money down the road replacing things a cheap inverter may burn out.

You've got lots of good advice regarding cabling etc from everyone else in this thread. The welding cables you have would be ideal IMHO - just get a crimp-on cable end for the alternator side and on the Tripp-Lite inverter itself there is are screw-down connectors. You may need some crimp-on nubs to insert into the inputs on the inverter as if I remember right anything lower than 2 gauge won't fit directly - I think 2 gauge JUST fit in when I installed mine.

I would strongly suggest 2 batteries minimum - even drawing only a few hundred watts (based on the equipment you mentioned) will draw down a single battery within an hour or two..and then you'd have to run the truck for at least 25-30 minutes to get any appreciable charge level back. Also remember that continued deep discharges (even in deep cycle batteries) can shorten the life of the batteries so you want to avoid discharging. A TRUE deep cycle battery (golf cart, for example) can be drawn down about 80%, but most hybrid deep cycles (Marine, for example) should only be drawn down to about 50%...so this can significantly shorten your runtime.

If you want the absolute best setup get a set of 6V golf cart batteries wired in series - they will last longer and perform better in the long run...and you can draw then down deeply and then charge fast.
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'97 C3500 Crew Cab Long Box Dually 6.5 Turbo Diesel.
Rebuilt with Navistar 506 block spring 2012
Special thanks to Racer55 and WhiteK2500 for their invaluable assistance!
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