Big current needs in bed of Gladiator. Home run, or 2nd battery and gauge concerns......

[steffen707]

Short time lurker, first time poster. Been spending all my time over the last year over at the Gladiator forum.

I'm planning to put a big inverter into the bed of my Gladiator, perhaps a 3000 watt one. If I do this I'll have to run heavy gauge wire (4/0 i've read) to the engine bay.

Instead of doing this, could I run smaller gauge wire from the engine bay to a secondary battery (with proper isolator and fuse of course) and then run the inverter directly off the secondary battery with the 4/0 gauge wire instead?

My thought was that the charging current to charge 2nd battery would be lower than the inverter demand. So i could get by with charging the 2nd battery with smaller wire, but then when i intermittently use the inverter, it would just drain down the 2nd battery until it gets charged up again.

Thoughts?

 

[john61ct]

Yes, but the size of the inverter is less relevant than the loads to be run through it.

That battery bank local to the inverter needs to be capable of supporting those loads, possibly at a high C-rate, with a minimum of voltage drop.

And also sized at a large enough Ah capacity to do so as long as they are run, without dropping much past 50% SoC.

Make an energy budget, how many amps, how long per day each load device, in order to make a more informed decision.

But the fat gauge cable feeding direct off your alternator will likely be cheaper, and

won't need replacing every two / few years.

 

[luthj]

What are you planning to power with your 3000W inverter, and for how long? Most sub 200AH batteries cannot supply the ~300A required for 3000W without dropping below the inverter cut-out. Such a draw would discharge a lead battery in 20 minutes. What is your alternator voltage? How often will you be using these loads?

There are ways to make it work like you describe, but more details is better.

 

[steffen707]

Thanks for the replys. You guys have given me much to research it appears.

I don't need the whole 3000watt capacity at once, but a 1500 watt inverter would almost be maxed out for some of the power tools I would like to run i'll have to do more research on that. i'm betting my table saw or circular saw only draw 1500watts at startup, but then drop to 1000watts or so.



I didn't realize that you had to have a big battery bank to draw 300A. I figured with cold cranking amps in the 600A range, it would be fine to pull 300A from it intermittently.

Alternator voltage is probably 13.5v

The loads will be used very short duration. I know a huge draw like that could drain a lead battery in 20 min, but I wouldn't be drawing that power continuously for that amount of time.

Even at 1500 watts, this site recommends I use 4/0 wire and have a 300amp fuse. I was trying to get away from the 4/0 wire, but that might be the easiest, more cost effective method.

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[luthj]

Most quality inverters can surge to 2x there rated power for starting inductive loads (motors/tools). This surge is not necessary for wiring calculations, just for inverter surge capacity.

CCA typically is measured and specified that the battery cannot drop below 7.2V. That is much too low to power an inverter.

Wiring size can be calculated with a voltage drop calculator. You are looking for less than 10% ideally.

Circuit Wizard - Blue Sea Systems

circuitwizard.bluesea.com

 

[steffen707]

CCA typically is measured and specified that the battery cannot drop below 7.2V. That is much too low to power an inverter.

ohh, so it can provide 600CCA but the battery could drop to 7.2V, but the same battery may only provide 100A and keep the voltage above say 12V?

 

[Ducky's Dad]

Might be simpler and ultimately cheaper to buy a 2000W inverter generator, like a Yamaha or a Honda. I have a couple of Yamahas and either one of them will run my miter saw and portable 10" table saw with no problems. The other one stays in the garage. Street prices for new ones are somewhat irrelevant because they often come up on Craigslist, either new or as new in the $600-$700 range.

 

[steffen707]

Wiring size can be calculated with a voltage drop calculator. You are looking for less than 10% ideally.
Circuit Wizard - Blue Sea Systems

So I just thought of this, if my starter battery and alternator can only supply 200A of power, and any draw that's more than that will result in the inverter under voltage limit to shut things down........

is there any reason to run a wire bigger than can handle 200A with a 3% voltage drop over the actual distance I need to run?

If not, then I probably should just run a 0 Gauge wire instead of 4/0 from engine bay to truck bed. Then if I need more current than can be supplied by the Alternator, i'll have to invest-IGATE in another option starting from the bed.

 

[steffen707]

Might be simpler and ultimately cheaper to buy a 2000W inverter generator, like a Yamaha or a Honda. I have a couple of Yamahas and either one of them will run my miter saw and portable 10" table saw with no problems. The other one stays in the garage. Street prices for new ones are somewhat irrelevant because they often come up on Craigslist, either new or as new in the $600-$700 range.

good point. I was trying to come up with a solution that works for my daily life, as well as some overlanding........Still might make more sense to have a smaller inverter in the truck and for bigger needs use a generator.

 

[luthj]

Battery and alternator can certainly supply more than 200A combined for short periods. Its a matter of math. If you are running a 1500W load with the engine running, you can expect the alternator and battery to carry the load at idle (about 130A). The voltage might sag a little, say from 13.5 to 13.2V at the battery. From there work out your voltage drop. I would say at least 11.5V at the inverter, so you have about 13.2-10.5=2.7V to work with.

Now if you need to run 130A with the engine off, that's a different matter. A 100Ah starter battery can probably supply 130A for a few minutes and maintain 11.3V, assuming its fully charged.


As an aside, 13.5V is not going to fully charge a lead acid battery that is being cycled regularly below 80% State of Charge (SOC). If you plan to discharge like this with any regularity, you will need a secondary charge source which can achieve the proper absorb voltage of approximately 14.4V. Solar, shore power, DC-DC etc. If you have the engine idling then the alternator can carry most of the load, so the battery won't discharge much.

 

[steffen707]

Battery and alternator can certainly supply more than 200A combined for short periods. Its a matter of math. If you are running a 1500W load with the engine running, you can expect the alternator and battery to carry the load at idle (about 130A). The voltage might sag a little, say from 13.5 to 13.2V at the battery. From there work out your voltage drop. I would say at least 11.5V at the inverter, so you have about 13.2-10.5=2.7V to work with.

Now if you need to run 130A with the engine off, that's a different matter. A 100Ah starter battery can probably supply 130A for a few minutes and maintain 11.3V, assuming its fully charged.


As an aside, 13.5V is not going to fully charge a lead acid battery that is being cycled regularly below 80% State of Charge (SOC). If you plan to discharge like this with any regularity, you will need a secondary charge source which can achieve the proper absorb voltage of approximately 14.4V. Solar, shore power, DC-DC etc. If you have the engine idling then the alternator can carry most of the load, so the battery won't discharge much.

Thank you for your help. I need to check what the alternator Voltage output is. I was just guessing its 13.5V, maybe its more like 14.5V. I'll look into it. I'm also thinking it would be a good idea to replace the starter battery with an AGM whenever it dies.

Now to complicate things, i've read about inverter/chargers. Am I understanding this correctly, they will convert from DC to AC when you need AC power, and also charge back up the DC battery when its getting electricity either from Solar or Shore power?

I know an inverter/charger is much more expensive than just an inverter......I'm just wondering if now is the time to buy one if I plan to run a Dometic Fridge in the future. I know I shouldn't plan to only use the lead/acid starter battery as the only battery if i'm running a Fridge. I just don't want to have to re-buy larger wire, or replace an inverter if a inverter/charger is really what my long term needs are.

Is there a good "guide to overlanding electrical systems/components"?

 

[luthj]

It's a steep learning curve.

A while back I put together a quick and cheap off grid electric system. With proper wiring it should run a 1500W load for short needs.

Framework for Inexpensive Off Grid Aux Electrical

Hey folks. A friend of mine asked for some advice on a basic electrical setup for a medium sized off-grid type vehicle. The major concerns were high value, reliable components, and Simple configuration. The components listed below have either been used/installed by myself, or have good...

expeditionportal.com

Inverter chargers make sense for large battery packs that are deeply discharged. The built-in charger can often supply 80+ amps. For a charger of that size, its typically cheaper to buy a combo inverter/charger, as the charger and inverter share about 75% of the same components. The combo unit also passes through 120V power to the outlets on the vehicle/RV when connected to shore power. For your application the extra cost doesn't make a lot of sense. At least not for a 100AH battery powering a fridge. You would be better served with a ~15A quality shore power/mains charger.

 

[steffen707]

It's a steep learning curve.

YEAH! I can see wasting several hundred to perhaps thousands if I underbuild OR overbuild a setup. I'll be sure to read your thread on the subject.

Inverter chargers make sense for large battery packs that are deeply discharged. The built-in charger can often supply 80+ amps. For a charger of that size, its typically cheaper to buy a combo inverter/charger, as the charger and inverter share about 75% of the same components. The combo unit also passes through 120V power to the outlets on the vehicle/RV when connected to shore power. For your application the extra cost doesn't make a lot of sense. At least not for a 100AH battery powering a fridge. You would be better served with a ~15A quality shore power/mains charger.

Oh, lol yeah the additional cost I was seeing was around $300-$500 if I recall.

Thanks again @luthj!

 

[steffen707]

A while back I put together a quick and cheap off grid electric system. With proper wiring it should run a 1500W load for short needs.

Framework for Inexpensive Off Grid Aux Electrical

Hey folks. A friend of mine asked for some advice on a basic electrical setup for a medium sized off-grid type vehicle. The major concerns were high value, reliable components, and Simple configuration. The components listed below have either been used/installed by myself, or have good...

expeditionportal.com

This was designed with lead/acid 6V duracell battery bank, right? So if there is 220AH total, how much of that capacity is usable? I thought i read not to go past 50% use from a lead acid, so around 110AH usable?

 

[john61ct]

Yes Duracell / Deka GCs are top value.

Really, consider a small portable inverter genset though to support your power tool usage