The Diesel Stop banner

Status
Not open for further replies.
1 - 20 of 27 Posts

·
Registered
Joined
·
3,010 Posts
Discussion Starter #1
I want to put a disconnect switch in the hot wire from the battery to the starter (actually the solenoid mounted on the starter) I once had a starter hang...the solenoid stuck in the on position and I had to scramble to get the batts unhooked before the starter caught fire. It was close...still smoking after 5 minutes. Anyway, ever since then I have wanted to put a disconnect switch on it, for emergencies, anti-theft, etc. I just need to know the amp draw before I buy one.
Thanks,
Jerry
 

·
Registered
Joined
·
3,010 Posts
Discussion Starter #3
Thank you very much. I had no idea it would be in the 600's. The highest I can find is a 500amp switch. Looks like I better keep looking.
Jerry
 

·
Registered
Joined
·
350 Posts
450-475 amps is what i used to measure
 

·
Registered
Joined
·
3,010 Posts
Discussion Starter #5
450-475 amps is what i used to measure
Thanks for the info. When you measured this, what was the conditions? Cold/Warm engine, outside air temp, weight of oil in crankcase?
Thanks,
Jerry
 

·
Premium Member
Joined
·
729 Posts
Jerry,
You will be fine using the 500 amp variety. It is plenty large enough. Disconnect switches are rated in the amount of current they can switch under load. When you use this switch it will normally not have a load on it.
 

·
Registered
Joined
·
350 Posts
Thanks for the info. When you measured this, what was the conditions? Cold/Warm engine, outside air temp, weight of oil in crankcase?
Thanks,
Jerry
I serviced a fleet of school busses for 3 years. That is the current draw a saw summer/winter, warm oil, cold oil, ford starters, reman starters. If we started to see something around 600 we would replace them. This was using a AutoMeter roll around tester with clamp on current probe.
 

·
Registered
Joined
·
3,010 Posts
Discussion Starter #8
Thanks guys. I'll pick up the 500 amp unit.
Jerry
 

·
Registered
Joined
·
9 Posts
I know, I'm brining up a old post but it is VERY pertinent to what I am doing. I want to put a fuse block next to the positive battery terminal on a 4 cylinder 92 HP tractor. (Case 1410)

I was thinking a 300amp fuse would handle it but now reading this am guessing I should be closer to 500amp for cold mornings? Or is that enough on a old tractor?

Was wanting to put this inline right after the terminal AmazonSmile: THOR Manufacturing THANLFB-300 300 Amp ANL Fuse with Block: Industrial & Scientific

the reason is because I added a battery shut off switch (it is rated to 2000amps) so when I am not on the tractor I can shut off the battery but then I got worried what if someday the cable protection got worn (as it is a tractor after all) and I wanted something to hopefully shut things down if that occurred.

Next question, if all of this works my plan is to do this on our 2001 7.3 Truck as well. What size does it need?

Thanks
E
 

·
Registered
Joined
·
2,040 Posts
Think about this: if the cable begins to wear, and makes just enough contact to pull 475A, the fuse won't blow, but the battery will still explode in a minute. So you've done nothing but cost yourself a lot of time & money. There's no point fusing a circuit that's supposed to draw over 200A - especially on an antique. And no: a 92hp 4-cyl. tractor starter doesn't draw 500A; it probably doesn't draw 150A, and it's still not worth fusing. Same for the truck - don't worry about it. How many times have you read on this or any other discussion forum about these trucks that "...it would've been OK if I had only added a fuse to the starter! :cry:"

Yeah: me neither.

BTW
Ford spec for normal cranking current is 230-630A on a '96 7.3L.
 

·
Registered
Joined
·
9 Posts
Both are vehicles I want to preserve and hold value with me. Considering the tractor takes a minimum of a 1050cca battery to start it and the truck takes a minimum of two 750s I figured if the line shorted it would spike over the 500amp fuse enough to blow it.
 

·
Registered
Joined
·
2,040 Posts
It might. But it takes more than 500A to blow a 500A fuse. By industry standard, it should last more than 100 hours at 550A, but blow in <1sec at 625A. This page explains how fuses are rated & designed:

(click this text)


So: do you want to arbitrarily pick another number, or stick with the 500A fuse?

The battery's CCA rating is almost irrelevant unless you live where it's always 0°. Otherwise, it's CA rating would be slightly more-useful, but not much, because they're just its design outputs under specific testing modes - not what it can put out in the real world. www.batteryfaq.org explains what those ratings & numbers mean. If you read that, you'll see that it's not particularly applicable to what you're imagining.

What's more important is: what does the starter ACTUALLY draw during cranking? As you can see from the example I posted above, it's a WIDE range on a big antique diesel engine. What really matters is: what exactly are you trying to protect, and FROM what? If the starter fails, there's no reason to protect it - it already failed. Fuses, fusible links, & circuit breakers are actually to protect the WIRING - not the devices. But with a wire capable of supplying a starter motor - especially a DIESEL starter - the concern becomes the BATTERY. Because drawing that much current from a battery for more than a few seconds will cause the battery to begin releasing Hydrogen, which will explode if the battery gets hot (and it does, producing that much current). So are you protecting the battery?

And now you say you want to "preserve" these antique vehicles - then preserve them as they were built, withOUT starter fuses. Clearly, they last & work safely that way because the vast majority of them never did or will have starter fuses.
 

·
Registered
Joined
·
9 Posts
I want to protect them from fire of the overall vehicle. I am not stuck on being stock. I just want to preserve the vehicle and memories. Both have VERY long hot wires coming from a battery that I worry could get shorted at some point. My biggest worry is wear and tear or animals. The tractor almost burned one other time from cattle chewing on wires and one pulled the starter wire. The truck fried a mouse quite well and it startled me. I did put quick release connects to the batteries and much of the time I take the positive off. On one I already installed and most likely on the other I will have a battery shut off switch but that is just to prevent draw on the battery when not in use as the Super Duty draws the battery and if left for a week or two in the cold winter months it is enough it might not start even with newer batteries.

But the SOLVE is that I want to protect the vehicle from fire caused by a short in the long cable coming from the positive batteries. I have found the mega fuses are designed for just that. TB_MEGA (littelfuse.com) and many hotrodder groups that mount their batteries in the trunk and have a even longer hot wire run to the starter are using them. Some are using250amp and some use 500amp.

For the 7.3 I was not sure but figured if I found one that worked for it since the cables are the same gauge it should work for the tractor to achieve the same goal of protecting from a short that would blow the battery or burn something else.
 

·
Registered
Joined
·
453 Posts
You seem determined to do it your way no matter the advice to the contrary so I'm not sure why you asked. You won't however find any credible source that recommends fusing a starter circuit. Many of us use battery disconnects on old vehicles but that's a completely different situation. I put battery disconnects on all my equipment so that I don't have to worry about phantom draws draining the battery on a machine that spends 98% of its life sitting there waiting for me to get around to starting a project that requires that particular piece of equipment. IMHO installing battery disconnects would be a much better alternative for you and would address most of the concerns you have identified.
 

·
Registered
Joined
·
9 Posts
I have those, the mega fuses are made for exactly what I was asking. Was just hoping a diesel group would know what these engines draw on a worst case scenario start before I get the fuse. I have already installed quick disconnect cables as well as a shut off switch on one. Just looking to go the extra mile. TB_MEGA (littelfuse.com)

All I wanted was Amp help. MANY have this setup but for most it is on gasoline hot rods, house batteries, etc. Have a nice day.
 

·
Premium Member
Joined
·
9,278 Posts
Your problem is that there are a lot of variables to come up with a actual amperage draw.

The starters age and condition are a couple of them along with the temperatures that it will be operating at. Not to mention the condition of the engine that you are trying to start.

Perhaps that is why 99.99% of vehicle starting systems don't have a fused circuit in them

Sent from my SM-J737V using Tapatalk
 

·
Registered
Joined
·
9 Posts
Your problem is that there are a lot of variables to come up with a actual amperage draw.

The starters age and condition are a couple of them along with the temperatures that it will be operating at. Not to mention the condition of the engine that you are trying to start.

Perhaps that is why 99.99% of vehicle starting systems don't have a fused circuit in them

Sent from my SM-J737V using Tapatalk
Its definitely a difficult balance. For me I am leaning to just default to one that would blow before the wire or battery would burn and call it good. The megafuses are designed to handle the spike a starter will have. I was just hoping someone here had done it and then saw the amperage discussion and thought that was a good spot to center in on first. The tractor unlike many cranks pretty easy even in the cold for its size. The truck.... well Any of you 7.3 guys know how much they love the cold. .... ..lol

All I have to compare to thus far are custom rod builds up to gas 454s, boats with smaller diesels or gas engines.
 

·
Registered
Joined
·
2,040 Posts
I want to protect them from fire of the overall vehicle.
A fuse will not put out a vehicle fire. A fire can start in a circuit that draws <10A, so a 250A fuse will not guarantee no fire.
I just want to preserve the vehicle and memories.
You have fond memories that involve a fuse being in the starter circuit??? The drama is getting pretty deep...
My biggest worry is wear and tear...
A fuse won't stop the wire from being worn or torn. Route the wire away from moving components so it doesn't get worn or torn - that works for every other vehicle on the planet.
...or animals. The tractor almost burned one other time from cattle chewing on wires...
Spray the wiring with insect repellent (DEET) periodically so it tastes bad.
...fire caused by a short in the long cable...
Again: a fire can be started with a fuse MUCH smaller than you're considering.
...mega fuses are designed for just that.
There is no fuse specifically designed for a starter - they're all specifically designed to burn out when their current rating is exceeded by 10-25%.
...hotrodder groups that mount their batteries in the trunk...
Hotrodders are generally not engineers, and are not known for creating "best practices".
...protecting from a short that would blow the battery or burn something else.
A fuse small enough to prevent that would be too small for the starter to work reliably.
 

·
Registered
Joined
·
9 Posts
A fuse will not put out a vehicle fire. A fire can start in a circuit that draws <10A, so a 250A fuse will not guarantee no fire.You have fond memories that involve a fuse being in the starter circuit??? The drama is getting pretty deep...A fuse won't stop the wire from being worn or torn. Route the wire away from moving components so it doesn't get worn or torn - that works for every other vehicle on the planet.Spray the wiring with insect repellent (DEET) periodically so it tastes bad.Again: a fire can be started with a fuse MUCH smaller than you're considering.There is no fuse specifically designed for a starter - they're all specifically designed to burn out when their current rating is exceeded by 10-25%.Hotrodders are generally not engineers, and are not known for creating "best practices".A fuse small enough to prevent that would be too small for the starter to work reliably.
Wow, thank you for absolutely nothing. Many of your comments exclude you form being any authority of any of this.

Many BOATS and custom cars have what I am looking for. They CAN prevent a catastrophic fire due to the main wire having an issue.
Deet doesn't stop cattle and it most likely would break down the insulation.

I already know it can and DOES work and has proved to save some boats and cars. I just wanted to save myself some trouble and see if someone had an idea on amperage as my tester only goes to 300amps and I was worried it could be more. You have a LOT of posts are 2000 of them crappy rude responses like this?

Oh and there ARE fuses made for this, I shared the link to them and their info. ...Have a nice day!
 

·
Registered
Joined
·
9 Posts
This guys give some good examples of necessary fuses for handling the battery bank and being able to start a motor. The problem is, his list doesn't go up to the HP I need.
Battery Bank Fusing Photo Gallery by Compass Marine How To at pbase.com

True to this thread, all I was asking was the amps starting a diesel engine (that I specified) might require.
The link above even shows how even good wiring can go wrong. I just want to protect as in the same scenarios.
"
Question: "Won't the starters inrush current blow my fuse?"

First, what exactly is "inrush current"? Inrush current is the very brief spike in current that the starter undergoes to get the motor to begin turning over from a stopped state. The inrush duration is usually about 200ms to 250ms long, and not long enough to blow a properly sized fuse. ANL, MRBF or Class T fuses are not sized for the inrush, they are sized to the wire they are protecting.
"

Guess I should have saved myself the time and just went ahead, got a larger tester and found out for myself. So much for the friendliness of fellow diesel heads. lol
 
1 - 20 of 27 Posts
Status
Not open for further replies.
Top