# Battery relocation to trunk; Breaker amperage?



## BlueGTIguy (Mar 6, 2003)

I plan on relocating the battery to my hatch. I will be using an Optima red top to avoid the use of a box, as well as the need to vent to atmosphere. Additionally, I will be using 2 AWG welding cable from McMaster (this should be sufficient, right?). For safety reasons, I plan on installing a breaker (or fuse?) inline from B+ to the starter. What is an appropriate amperage rating? No serious aftermarket electrical accessories, stock 90 amp alternator. Any other suggestions for this project?


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## DubRadio (Oct 15, 2003)

*Re: Battery relocation to trunk; Breaker amperage? (BlueGTIguy)*

get a new alt, like the 110 amp . b/c the power going from the alt to the batt takes a longer distance and power loss will happen from heat
try using 0 guage wire also, it provide a larger pipeline for that power to flow through


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## Realtech (Jan 18, 2004)

*Re: Battery relocation to trunk; Breaker amperage? (BlueGTIguy)*

you need to fuse or put a circuit breaker at each end of the cable connecting the auxillary battery to the charging system. There will be huge amounts of current stored in both batteries. if a short occurs and there is only a fuse at the front of the cable, then the rear battery will continue to discharge it's current into the short....That would be really bad. --"Thermal Event Bad"


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## Realtech (Jan 18, 2004)

*Re: Battery relocation to trunk; Breaker amperage? (BlueGTIguy)*

Oh yeah, and 2 guage should be fine, but the 0 Guage would be better. for fuses i woudl use at least the maximum current that you could expect the devices being run off of the rear battery to draw. In other words, add up the total current draw for all of the devices which are attached to the rear battery and then use that fuse value at both ends of the cable.


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## BlueGTIguy (Mar 6, 2003)

*Re: Battery relocation to trunk; Breaker amperage? (Realtech)*

Just to be clear, this is a handling improvment; I'm putting the ONLY battery in the hatch; the one that normally resides under the hood will be relocated to the hatch. This is ONLY for better weight distribution, nothing to do with electrical devices. I figure the stock battery cable is somewhere between 2 and 4 AWG, so high quality 2 AWG should make up for the extra distance. 100 amp breaker at the battery end?


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## VeeDoubleYouGuy (Nov 4, 2003)

*Re: Battery relocation to trunk; Breaker amperage? (Realtech)*


_Quote, originally posted by *Realtech* »_Oh yeah, and 2 guage should be fine, but the 0 Guage would be better. for fuses i woudl use at least the maximum current that you could expect the devices being run off of the rear battery to draw. In other words, add up the total current draw for all of the devices which are attached to the rear battery and then use that fuse value at both ends of the cable.

are you serious man? thats not how it works. see cuz first of all there's one battery. second, you're not worried about accessory amperage because even if you were using all 90 amps that the alternator can give you're still way under what the starter needs (~500amps). The main positive cable has to go directly to the starter.


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## Realtech (Jan 18, 2004)

*Re: Battery relocation to trunk; Breaker amperage? (BlueGTIguy)*

Even with just one battery you should fuse both ends of the cable, b/c the alternator supplies current while the car is running. The fuse is really meant to protect the cable -- not the battery. 100amp fuses or Circuit breakers should be fine. the wire gauge sounds all right too.


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## VeeDoubleYouGuy (Nov 4, 2003)

*Re: Battery relocation to trunk; Breaker amperage? (Realtech)*

ok do me a favour and bench test a starter and tell me how many amps it draws.


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## 2.ohh (Jun 21, 2002)

*Re: Battery relocation to trunk; Breaker amperage? (VeeDoubleYouGuy)*


_Quote, originally posted by *VeeDoubleYouGuy* »_ok do me a favour and bench test a starter and tell me how many amps it draws.


you got a point there, and it's easy to prove. why would we need high CCA batteries if it only took 100 amps to turn over a starter?







they have extremely high current draw, which is why the line off the battery to them is not fused. that is also the reason why you should not relocate your only battery to the trunk. you need to fuse both ends, since if you don't you can start a fire in your car. you would also need two 1/0 cables running from the battery back up to the front for the starter to get enough current transfer without burning up your wire.


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## wptrx7 (Dec 20, 2002)

what? i need to hang out on this forum more. 2.ohh can you explain why you need to run 2 1/0 wire. blue gti guy, do yourself a favor take a look at jegs.com and summitracing.com , look at the kits they offer for battery relocation. and if you are running your battery to the back for wieght that leads me to believe you are racing, if it is legal, most require that you have a battery in a box or the j brackets are welded to the body?


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## BlueGTIguy (Mar 6, 2003)

*Re: Battery relocation to trunk; Breaker amperage? (2.ohh)*


_Quote, originally posted by *2.ohh* »_...that is also the reason why you should not relocate your only battery to the trunk. you need to fuse both ends, since if you don't you can start a fire in your car. you would also need two 1/0 cables running from the battery back up to the front for the starter to get enough current transfer without burning up your wire.

I didn't think of starter current draw issue until after I posted... Anyway: 
1. Summit Racing sells a kit that comes with 2 or 4AWG, no fuses or breakers; I know of a few folks on the Vortex using this kit. 
2. Factory battery-to-starter cable is approximately 4AWG. Granted, it's a short run of cable, I've never heard of anyone frying one of these. Upgrading to 2AWG (or larger if deemed necessary) should compensate for the extended run.
3. Lots of performance cars come with the battery in the trunk from the factory; no issues with fires, I'm sure Ralph Nader would have pointed them out if there were any.

So what's the verdict?


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## Houston R32 (May 23, 2003)

*Re: Battery relocation to trunk; Breaker amperage? (BlueGTIguy)*

Why don't you just buy one of the kits? They look like all the right pieces, including the battery hold down tray. I might consider a long ground strap as well, depending on your attitude on grounding kits.
You can't fuse the line. The starter current draws are huge. Back in the days of the Mayflower when I was doing engine controller design the biggest problem we had was trying to keep 5 volts to the computer during starting. Voltage dropped to about 6 volts for a twelve volt system on initial cranking and most voltage regulators had a 1.5 volt dropout. National finally solved it with a special regulator with a .5 volt dropout. But think about the currents involved to bring the 12 volt system down to 6 volts.
My 928 had the battery in back (under the spare tire - very hard to get to). I believe almost all Porsches have the battery at the end opposite the engine. My BMW 850i had two batteries in the trunk, one on each side. No fuses in those starter lines.


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## BlueGTIguy (Mar 6, 2003)

*Re: Battery relocation to trunk; Breaker amperage? (Houston R32)*

The kits usually come with 2awg, which sounds like it might be a little wimpy (especially when 1/0 can be had for under $2/foot). Additionally, the boxes that come with the kits are crappy $8 Poop Boys marine boxes, and they're not NHRA approved (doesn't matter, I don't drag race). Kinda pointless if you ask me. I still have some homework to do regarding mounting the sucker (don't want a 60lb projectile sailing towards my head in the event of a rear-end collision). For now, I'm just curious about the electrical considerations. Thanks for all the replies.


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## 2.ohh (Jun 21, 2002)

*Re: (wptrx7)*


_Quote, originally posted by *wptrx7* »_what? i need to hang out on this forum more. 2.ohh can you explain why you need to run 2 1/0 wire. 


simple, if you have a starter that draws 500 amps, and you have a longer run of cable, you HAVE to increase the size of the cable. and being that it will be running through the car, i'd want to make absolutely sure there was no chance of the cable catching fire from drawing too much current through it. let's guestimate that you'd need 15 ft from the front of the car/starter to the battery in the trunk. 4 guage will support about 125 amps for that length, going by iasca standards. 2 guage would support almost 200 amps. 1/0 will support under 400 amps. granted for shorter bursts, like in starting a vehicle, it's not *as* important to have the cable that meets the standards, but what happens when it's cold and it takes more than a few turn overs to start the car? in that case you'd be drawing all that current for a longer period of time, and that could cause a fire. i'm not saying it will, but i'm just warning you of the possible consequences. i personally won't run 1/0 cable for more than 300 amps, cause i've seen improper wiring/installs catch on fire.
also, how long would you say the stock 4 guage cable going to the starter is? i know mine is about 3 ft. 3 ft of 4 guage will support about 500 amps. the reason why the kits don't come with circuit breakers or fuses is that they don't make them big enough to allow the current for the starter, and you can get a 300 amp ANL fuse, but it's designed to be installed inline with 1/0 cable. the fuse/circuit breakers are there to protect the wire and nothing else. since you can't fuse the battery in the trunk, make sure you are extra careful in installing the wire to it. if by chance it rubs on some metal and it cuts through the jacket, expect a fire. there will be no fuse to stop the flow, and it will just keep grounding the battery out, which will lead to a fire and possibly fry all the electronics in the car. but i guess i have no idea what i'm talking about, even though i've rewired entire vehicles, i install stereos, and i'm an iasca certified judge


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## Pagano (Sep 24, 2001)

*Re: (2.ohh)*

I ran 1 gauge Industrial cable, the stuff that has like 12 strands in it.
No fuses, no breakers, and no fire
wooo luck








Not for nothing, the extra length should in no way invoke a fuse, if you compensite with the right diameter wire for the cause, then there is no need, factory isn't fused. WORST case sceneraio that would require a fuse is if the jacket is rubbing, gets cut and shorts.
I've rewired entire cars, installed my fair share of stereos, but I lack the judge license...boo hoo, suppose my side is invalid then, but I'll throw in another useless tag, I was once nominated employee of the month


_Modified by Pagano at 10:51 PM 4-23-2004_


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## 2.ohh (Jun 21, 2002)

*Re: (Pagano)*


_Quote, originally posted by *Pagano* »_
Not for nothing, the extra length should in no way invoke a fuse, if you compensite with the right diameter wire for the cause, then there is no need, factory isn't fused. WORST case sceneraio that would require a fuse is if the jacket is rubbing, gets cut and shorts.



the reason why the stock wire going from the battery to the starter is not fused is because A) they don't have fuses large enough, and B) it's not going to set the car on fire, CAUSE IT'S NOT RUNNING THROUGH THE CAR!!! is this so hard to grasp? oh wait, you must get it, cause even you said "worst case scenario that would require a fuse is if the jacket is rubbing, and gets cut and shorts" THAT IS THE WHOLE POINT OF FUSING A POWER LINE GOING THROUGH YOUR CAR!!! that is why i said that if you are running a wire and not fusing it, make sure to take extra special precautions to make sure nothing can rub it or cut it. thank your for arguing my point for me







a fuse connected to a power line is NEVER there to protect the equipment it's hooked to. that's why audio equipment has it's own fuses. the main power line fuse is to protect the WIRE and your CAR. this is so simple to understand, yet you guys just aren't grasping it. 
if you are wondering why i keep on with this, it's because if by chance what i am saying prevents 1 person from having a fire in their car, well then i helped out. i might not be the nicest person in the world, but i do know my sh!t.


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## Realtech (Jan 18, 2004)

NHRA requires an external battery cut-off switch at the back of the car. This is their idea of "protecting" or shutting down the elec. system in the even of a fire. Fuses CB's ar supposed to do that.


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## 2.ohh (Jun 21, 2002)

*Re: (Realtech)*


_Quote, originally posted by *Realtech* »_NHRA requires an external battery cut-off switch at the back of the car. This is their idea of "protecting" or shutting down the elec. system in the even of a fire. Fuses CB's ar supposed to do that.


as a thought on this, to "keep things safe" but still allow the battery relocation, check out this:
http://www.carsound.com/columns/navone/
i had been looking for the link to it for the past few days. it's gonna be pricey, but if you want to do it the safe way, that's the way to go.


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## Realtech (Jan 18, 2004)

*Re: (2.ohh)*

that sounds like it'll do the job. i not so sure that I like the 15 second lag though. The web page says the ICB opens when is sees the threashold currend for 15 seconds or more. That seems too long. Fuses blow in under a second.


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## 2.ohh (Jun 21, 2002)

*Re: (Realtech)*


_Quote, originally posted by *Realtech* »_that sounds like it'll do the job. i not so sure that I like the 15 second lag though. The web page says the ICB opens when is sees the threashold currend for 15 seconds or more. That seems too long. Fuses blow in under a second.


read further on the page:

_Quote »_If the main power cable of an ICB is short circuited to chassis ground, the switch will open within 5 mS (.005 seconds).

the 15 seconds is just for a little over the rating, not a short circuit. kind of like how my sub amp is rated at 150 amps, but i know it'll draw 192 at full power. fuses are the same way, they'll allow over their rating for a short period of time, but keep it up and they will pop. short them out and the blow, same as the ICB opens in .005 seconds.


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## Non_Affiliated (Feb 12, 2002)

*Re: (2.ohh)*

Before you guys discuss startes anymore, realize that most starters have a Rating of 1.3KW to 1.5KW draw of power. There may be a instantanous surge current of maybe 200 amps, due to it being a DC motor.
Also there are seveal automotive manufactures that actually locate the battery in the trunk, BMW comes to mind.


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## Res Dog (Mar 28, 2004)

*Re: (Non_Affiliated)*

2.ohh is right on the money here...pay attention!
personally if my only battery would be in the rear of my car, I would be running 2 runs of 1/0 welding cable (hell, its cheap...) with each single cable sporting a 300A ANL fuse inline, close to the battery...fuses ARE necessary in this scenario because there is the risk of a fire if you have a chassis short...I had a friend helping me run some of my 1/0 in the rear of my car and when he wasnt paying attention he managed to ground it out on some bare steel around the spare tire well where I was relocating the battery too, and in the instant it took to pop the fuse, he pretty much melted a hole in the sheet metal and welded the cable to the steel...if there was no fuse there, think of what 2400 CCA and 8 hrs of reserve would have done to the thin sheet metal of my poor datsun!
you probably wont be running anywhere near the same power, but why take the risk when a few extra bucks can let you rest at ease? I honestly never used to believe in fuses, the only reason I had them in the car was because I was accentuating the rest of the monster cable gear that I have in the car and the M-Power fuse went along nicely with the battery terminals







that one experience made me realize the folly of my ways heh, and how lucky I had always been previously...


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## 2.ohh (Jun 21, 2002)

*Re: (Non_Affiliated)*


_Quote, originally posted by *Non_Affiliated* »_Before you guys discuss startes anymore, realize that most starters have a Rating of 1.3KW to 1.5KW draw of power. There may be a instantanous surge current of maybe 200 amps, due to it being a DC motor.
Also there are seveal automotive manufactures that actually locate the battery in the trunk, BMW comes to mind.









my 1.6L protege has about a 400 amp draw. i measured that with my clamp meter, when i was contemplating moving my battery to the trunk, for stereo purposes








and when a manufacturer relocates the battery, they make damn certain that there is no way the wire will ever be rubbed against.


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## slumberbunny (Feb 10, 2003)

*Re: (Non_Affiliated)*


_Quote, originally posted by *Non_Affiliated* »_Before you guys discuss startes anymore, realize that most starters have a Rating of 1.3KW to 1.5KW draw of power. There may be a instantanous surge current of maybe 200 amps, due to it being a DC motor.
Also there are seveal automotive manufactures that actually locate the battery in the trunk, BMW comes to mind.

Where did that come from? Motors are not measured in KW (sure, there's like 730watts/1hp whatever). The fact is by that standard I=P/E; therefore I (current)=1500/12 or 125amps.
Where did you get the number of 1.3 to 1.5kw? Just curious...


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## Non_Affiliated (Feb 12, 2002)

*Re: (2.ohh)*


_Quote, originally posted by *2.ohh* »_








my 1.6L protege has about a 400 amp draw. i measured that with my clamp meter, when i was contemplating moving my battery to the trunk, for stereo purposes








and when a manufacturer relocates the battery, they make damn certain that there is no way the wire will ever be rubbed against.

What kind of clampmeter? and was it calibrated? I ask cause I have seen the market on some clamp meters and what you read on the box isn't always trtue into the accuacy of a clamp meter. Theat and the fact that you are taking a reading on a inductive motor.


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## 2.ohh (Jun 21, 2002)

*Re: (Non_Affiliated)*


_Quote, originally posted by *Non_Affiliated* »_
What kind of clampmeter? and was it calibrated? I ask cause I have seen the market on some clamp meters and what you read on the box isn't always trtue into the accuacy of a clamp meter. Theat and the fact that you are taking a reading on a inductive motor.


http://www.sears.com/sr/javasr...59000
i tested the starter draw shortly after i purchased that meter. thank god for sears charge cards, otherwise i wouldn't have such a nice one







i use a small radioshack DMM for basic uses, but i have that clamp meter as well as an older analog meter for more precise measurements.


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## Non_Affiliated (Feb 12, 2002)

*Re: (slumberbunny)*


_Quote, originally posted by *slumberbunny* »_
Where did that come from? Motors are not measured in KW (sure, there's like 730watts/1hp whatever). The fact is by that standard I=P/E; therefore I (current)=1500/12 or 125amps.
Where did you get the number of 1.3 to 1.5kw? Just curious...









Well actually 746 watts equals 1 HP. And honestly both are correct for determining the work that the motor does.


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## Non_Affiliated (Feb 12, 2002)

*Re: (2.ohh)*

So I ask how did you test starter current? I don't ask these questions to be an arse. Just that improper testing can lead to erroneous readings. Did you use the min max function or just a quick turn or two on the starter and use the reading.


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## Wiggles (Feb 9, 2004)

*Re: (Non_Affiliated)*

well just FYI to the world, I, just yesturday relocated my battery and seem to have broken a couple rules and still am okay!
I installed an optima yellow top D34/78 Deep Cycle in my trunk and ran Rockford Fosgate 1000+ Purified copper strand 4AWG from the battery to a little power distribution block in the engine bay and then onto the starter solenoid and alternator using the same high quality 4AWG. For reference there was no fuse used inbetween the battery and the feed to the engine bay. Also the wire was tripple wrapped(insulated) in electrical tape to help make sure the shielding didn't rub or break, then held in conduit. 
Now if there was 500 amps of curent charging through that, it only being 4 gauge, it would get burning hot and possibly start to warp, melt or constrict. After reading this post you all got me plenty scared but I had done a lot of physics and just recently got done designing an acoustic engineering course at our local community college (though no I am not a judge or a mechanic nor a professional installer) and during that course creation I was required to study ohms laws and the surrounding electrical theory pretty extensively and I realized that a lot of what I was getting spooked by in this post was not true, so I went ahead and was confident that a good line of insulated 4 gauge was more than sufficient. I not only started the car perfectly, I shut it down and started 3 times in less than a minute to test how much heat would be generated. When I went to the distribution block and removed the tip of the wire to feel it, it was still totally cool. One start at 500 amps may quickly cool but three in rapid fire would melt the wire, so that rating is obviously wrong, sorry to say it, but it has to be or my car would be in the middle of an electrical fire. Secondly I let the car idel for over 25 minutes to see how well the charging would be handled by this puny 4 gauge and you know what, not only was it perfectly cool after all of the that load, the voltage stayed at a constant 13.65 volts at the battery (some being taken out for the ignition system, that is a damn effiecient transfer).
So what is all this comming to, it is comming to the point that while I hate to say that all of your theory sounded good and you may have had one bad experience where you saw something go wrong in the field, a good portion of the propoganda towards him frying his car if he doesn't go overboard with heavey wire is bull shiat. I will be more than happy to throw pics to any of you that don't believe I did this install as I did. So good luck to anyone doing a relocation and to those of you whom are a little more practically minded, thanks for not hyping the paranoia!


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## 2.ohh (Jun 21, 2002)

*Re: (Non_Affiliated)*


_Quote, originally posted by *Non_Affiliated* »_So I ask how did you test starter current? I don't ask these questions to be an arse. Just that improper testing can lead to erroneous readings. Did you use the min max function or just a quick turn or two on the starter and use the reading.


peak hold for the first test, which was 398 amps. just for test purposes i removed my spark plug wires and had my buddy turn it over for 3 seconds. i just observed the reading, and by the end of the 3 seconds it was down to 328 amps, which i am assuming was because the starter was already spinning, and did not need that burst to get it moving. i don't know a ton about this, i just know that if i run a power cable through my car, i'm going to take every precaution i can http://****************.com/smile/emthup.gif


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## 2.ohh (Jun 21, 2002)

*Re: (Wiggles)*


_Quote, originally posted by *Wiggles* »_Secondly I let the car idel for over 25 minutes to see how well the charging would be handled by this puny 4 gauge and you know what, not only was it perfectly cool after all of the that load, the voltage stayed at a constant 13.65 volts at the battery (some being taken out for the ignition system, that is a damn effiecient transfer). 


with all your studying you didn't learn through ohms law that it's not the ignition system that is lowering the voltage to the battery, it's the 4 guage wire you used. there is a reason why people use large cables for high power amps, voltage loss. voltage loss = less power output from amplifiers. 4 gauge wire over 15 ft with 100 amps running through it will create a .375 volt drop. 1/0 would create a .118 volt drop. if your alternator is charging at over 14 volt, like most do, you might also want to check all your connections, especially your ground. ever poor connection, and a bad ground will add to the voltage drop.
that yellow top battery you installed has an internal voltage of 13.2 volts. on an alternator is needs 13.8-15 volts to properly charge it. check you alternator's voltage. if it's 14.2-14.5, definitely check and retighten all power connections, and if that doesn't increase the voltage at the battery, try a different/better ground. if you can, run a 4 guage cable from your grounding point at the battery, then outside your car, and up to your engine block to see if the voltage at the battery increases. if it does, i would highly recomend installing an additional 4 guage cable for the ground. trust me when i say that yellow top batteries are VERY picky about how they are charged, especially when they've been deep cycled.
http://www.optimabatteries.com...8.pdf
you've already installed it all, and i'm not going to say to take it out, but i would highly suggest at least upgrading to 1/0 cable, a 300 amp fuse (since they will support 2-3 times their rating for short bursts), and using the cable you already have run for an additional ground wire. think of the additional ground wire as a "hyper ground" kit. it just improves the ground connections between the major components in an engine bay. i'm not talking out my [email protected]@, i'm giving real world recomendations to protect your car and your battery. if you keep the voltage low to the battery, your alternator cannot maintain it, and it will prematurely die.


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## Non_Affiliated (Feb 12, 2002)

*Re: (2.ohh)*


_Quote, originally posted by *2.ohh* »_

peak hold for the first test, which was 398 amps. just for test purposes i removed my spark plug wires and had my buddy turn it over for 3 seconds. i just observed the reading, and by the end of the 3 seconds it was down to 328 amps, which i am assuming was because the starter was already spinning, and did not need that burst to get it moving. i don't know a ton about this, i just know that if i run a power cable through my car, i'm going to take every precaution i can http://****************.com/smile/emthup.gif 


First off Peak hold is not the function to use that will only show the highest level reading that the meter has read. How do I know, well I work at Fluke for 4.5 years as a repair/Calibration tech.
Honestly the best best way to look at stater current draw is with a DMM with logging capability, A Data logger/Recorder, or some piece of equipmemnt that has a logging feature. 








In this image is a Gas engine stater current draw, granted not sure what size engine. But remember that the more cylinders usally the more current neded to crank the engine over. Also Compression usally plays a role as more energy is needed to over come the forces of the compression stroke.
If you were running a TDI, 328A wouldn't probably be all too unreal.


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## 2.ohh (Jun 21, 2002)

*Re: (Non_Affiliated)*

damnit, don't tell me that







now i want to go out and get another meter







not before an osilloscope and smaller RTA


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## Non_Affiliated (Feb 12, 2002)

*Re: (2.ohh)*


_Quote, originally posted by *2.ohh* »_damnit, don't tell me that







now i want to go out and get another meter







not before an osilloscope and smaller RTA









Man I hate to say your a day late and a dollar short but a couple months back an installer friend of mine, I sold hime my Hitachi V-425 Dual trace, 40Mhz scope. The nice thing about it was it had Cursors that would give you the P-P voltage read out in the corner and the time/div between the two. I just didn't need it since I use my 123 20Mhz handheld scope.


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## 2.ohh (Jun 21, 2002)

*Re: (Non_Affiliated)*


_Quote, originally posted by *Non_Affiliated* »_
Man I hate to say your a day late and a dollar short but a couple months back an installer friend of mine, I sold hime my Hitachi V-425 Dual trace, 40Mhz scope. The nice thing about it was it had Cursors that would give you the P-P voltage read out in the corner and the time/div between the two. I just didn't need it since I use my 123 20Mhz handheld scope.


did i ever tell you that you suck?







if you come across any other good deals on test equipment, let me know http://****************.com/smile/emthup.gif i scrounge around some local electronic surplus places, but even their oscilloscopes that are old and beat up are over priced. i can get new ones online for just a little more.


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