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Electrical system load measurements?

dyeager535

dyeager535

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Anyone ever tested to see what the electrical system load is for a TBI truck idling with minimal accessories on?

How about one of the gear reduction starters cranking a SBC?

One of the clamp amp meters is on my wish list, but I don't have access to the truck anyway, so if anyone already has figures that would be helpful.

The draw numbers I've been able to find are all over the place, and I'm sure there will be some variation, but I'd rather get what is true for someone here, dealing with a pretty similar rig to mine.
 
Tested an 04 seirra 5.3 the other day. Alt had quit,was running on the battery. Was using .2ish volts to running engine. Ac, lights, and radio were off, door was open.
 
I can't see how a running truck of that vintage could draw only .2A, and even if an amp clamp was in the wrong range, even 2A is too low (PCM, injectors, ignition, fuel pump, cluster, 12 other modules, blah, blah). It could be voltage drop, but that doesn't really tell us anything since we don't know the resistance, so I'm going with fat-finger.

I'll enter the betting pool at 8A, all lights off.
 
Sorry. Bad typing pre coffee.

Yes .2v drop running 5.3 at idle.
I tested it backwards. It was running when i arrived with volt meter battery showed 11.5v alt lead showed same. Engine off was 11.65v thou I didn't wait to long for battery to come to full rest
 
Unfortunately I'm trying to estimate capacity and cranking amp requirements for a battery, so I need draw in amps.

I found one chart that calculated over 30 amps with minimal draw, I just don't see the trucks electrical system drawing that without all the accessories running.

120-720 amps are the range I'm seeing via Google, which is just too big a spread to make an assumption. Obviously there are a lot of variables that can affect the numbers, but a mild compression 350 with mini starter would seemingly have fairly standard results, and as many SBC's are out there, I'm surprised it's not easier to find.
 
The problem w/ what you're pulling up there is instantaneous amps can be extremely high getting started. Measured in milliseconds. And that's where that 700amp number came from.

Continuous starting will be far lower than that. Probably in the 200a range.
 
JoshHefnerX said:
The problem w/ what you're pulling up there is instantaneous amps can be extremely high getting started. Measured in milliseconds. And that's where that 700amp number came from.

Continuous starting will be far lower than that. Probably in the 200a range.
Click to expand...
Most cars nowadays have a 100a fuse for the starter.
Our trucks probably should be in the 200a but the gear reduction starter might be closer to 150a
I can probably get that number soon but I don't run my tbi anymore so I can't get that number, it might be a little lower than my vortec though so I can get you that number sometime this week
 
Unfortunately my analog Vat30's amp guage is not able to read small amp draws accurately.
Have watch many starters draw. Old school large copper starters 200-300 amps on well tuned sbc starting in 5 seconds or less.
permanent mag 120 to 200 same engine.

Then it would come down to the requirements for an HEI, all you need.
 
Wes Harden said:
Unfortunately my analog Vat30's amp guage is not able to read small amp draws accurately.
Have watch many starters draw. Old school large copper starters 200-300 amps on well tuned sbc starting in 5 seconds or less.
permanent mag 120 to 200 same engine.

Then it would come down to the requirements for an HEI, all you need.
Click to expand...
HEI and fuel pump.
Which I believe should be a little less than my vortec fuel pump usage
 
JoshHefnerX said:
The problem w/ what you're pulling up there is instantaneous amps can be extremely high getting started. Measured in milliseconds. And that's where that 700amp number came from.

Continuous starting will be far lower than that. Probably in the 200a range.
Click to expand...

I suppose that's true, perhaps some meters simply aren't fast enough to grab the inrush peak, and the ones that can are where the highest numbers originate? I suspect the initial millisecond draw figure isnt that important, as long as the starter can pull enough to actually start rotating the engine.

I'd be happy to hear any figures people can pull off their trucks for starting or idling.
 
You already know that a regular car battery will start it, so where are you going? Lithium cells? Supercap bank?
 
Yeah, playing around with the idea of lithium (lifepo4, not interested in lithium ion).

On the starting side clearly you need to know the draw to get the right battery, but the ones that will fit the lawn tractor (the ultimate destination) could also be useable in the truck, you just have to get one that is able to support the starters draw. Don't see a downside getting one that will work in the truck if needed.

I'd like to get a baseline draw to see how long the truck could run without an alternator.

Worst case it could pull double-duty as a jump starter.

The prices have come down enough that the two-year lifespan lead acids for the lawn tractor don't really make sense anymore, at least to me. If I got one that could be useful for more than just the tractor, why not?
 
1 question I have. How well will the charging systems work on lifepo4. If not what mods needed.
 
Making one work in place of lead-acid relies on a BMS. The ones you buy have it built in. https://www.amazon.com/TYKOOL-Firep...Bilt-Generator/dp/B0DK1M4V8B/ref=sr_1_1_sspa? If rolling your own, you'll have to add some kind of BMS. For a car, you can get more voltage just by putting a diode(s) in the sense line. A lawn tractor is typically a pretty poor charger, with voltage varying a lot with engine speed. You can probably verify ahead of time it's able to make 14V or more.
 
So your concern is that a lithium pack will not need as many Ah to get the required CCA, hence the reduced run-time without an alternator?

How often does this really happen? If you really want extended run-time, swap in a 6.2. They can run all day with no alternator as long as you keep the lights off.
 
Wes Harden said:
1 question I have. How well will the charging systems work on lifepo4. If not what mods needed.
Click to expand...
I don't know that answer but I do know Dakota lithium, a US BASED company is selling automotive batteries now in the LifePo variety.
They started with the deep cycle, then made a starting battery.
I just can't stomach the price yet but they have an unconditional 11 year warranty.
LifePo has a big advantage that voltage is more flat for longer then drops sharply.
You easily get 30% - 50% more usable voltage before the battery is dead.
I have been considering this for a while
 
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I'm in the process of swapping my trailer over to lifepo4. In the process my trailer needs an upgrade to the charger as the voltages used on lead acid only gives about an 80% charge. Need to be about 14.6v for most of the bulk charging or you wont ever get a full batt.
 
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