Battery Terminal Fuse

[peteco]

Occasionally I see mention of a terminal fuse. Sounds like a good thing to have. If all the circuits already have their own fuse or breaker, then the terminal fuse is primarily covering a short to ground between the battery and the first fuse/breaker in the line, which is either a 30 or a 50 amp in my Roadtrek 210. The terminal fuse would also be a backup in case one of the others failed closed. I would think the terminal fuse should be upsized somewhat so the other fuses or circuit breakers activate first. Am I missing anything here and any thoughts on sizing?

https://www.amazon.com/Bay-Marine-Si...K667D49AR&th=1

[dicktill]

Originally Posted by peteco

Occasionally I see mention of a terminal fuse. Sounds like a good thing to have. If all the circuits already have their own fuse or breaker, then the terminal fuse is primarily covering a short to ground between the battery and the first fuse/breaker in the line, which is either a 30 or a 50 amp in my Roadtrek 210. The terminal fuse would also be a backup in case one of the others failed closed. I would think the terminal fuse should be upsized somewhat so the other fuses or circuit breakers activate first. Am I missing anything here and any thoughts on sizing?

https://www.amazon.com/Bay-Marine-Si...K667D49AR&th=1

Hi Pete,

That is the perfect battery terminal fuse and holder; I have a bunch of them on my more complex system.

Regards, Dick

P.S. / personal rant: Please buy from someone other than Amazon. It has been rare here lately that anyone references items from anywhere else. If everyone buys everything from Amazon, soon there won't be anyone else to buy from! I don't think Jeff Bezos will starve.

[markopolo]

Dick - It would probably help if you think of Amazon as a platform that facilitates sales.

Third Party sellers total sales exceed Amazon first party sales on the platform and have done so for a while now.

amazon.png

In the example Pete provided he's buying from a smaller business - which I think was the point you're making.

Here's the sellers profile:

Mobile Power Pros storefront

5 out of 5 stars99% positive in the last 12 months (301 ratings)
Bay Marine Supply is a family-owned marine retailer based in San Diego, California. All of our staff are active sailors, and we are familiar not only with all of our products, but with the service and support that our customers deserve. Our goal is nothing less than 100% satisfaction, and we're happy to answer any questions, before or after your purchase.

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I think Avanti first mentioned that type of fuse on this forum and I agree with Dick that they're a great choice.

Size them according to the wire size being protected.
Fusing is needed at the source of energy such as a battery.
If there are two battery banks separated by wire then there should be fuses on each end for example.

[booster]

Originally Posted by markopolo

Dick - It would probably help if you think of Amazon as a platform that facilitates sales.

Third Party sellers total sales exceed Amazon first party sales on the platform and have done so for a while now.

Attachment 8093

In the example Pete provided he's buying from a smaller business - which I think was the point you're making.

Here's the sellers profile:

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I think Avanti first mentioned that type of fuse on this forum and I agree with Dick that they're a great choice.

Size them according to the wire size being protected.
Fusing is needed at the source of energy such as a battery.
If there are two battery banks separated by wire then there should be fuses on each end for example.

One warning on them is to make sure they are assembled per the instructions. When the fuse is mounted, no washer under it only on top, even though it looks (to me anyway) like a washer underneath would be good. They can and will overheat with the washer underneath, which I know from experience.

[markopolo]

I learned about not putting a washer underneath from experience also. It was a different type of fuse but still applies for any connection like that.

A quick test is to feel for heat. I put a 500W load on the system as part of a test and was working near the fuse and felt the heat coming off it. The cause was a washer underneath.

[avanti]

Yeah, MRBF fuses are the best.

You can get them cheaper at Waytek:

https://www.waytekwire.com/products?...bf&pageSize=36

You have to order the pieces a-la-carte. Note that you can get two-gang fuse holders, which lets you build a little bus right at the battery.

They are also useful if you want to put a fuse on a second=alternator output as well Whether this is a good idea is a different question. This issue is that if it blows, it will remove the load from the alternator, which will likely damage the alternator. OTOH, if it blows, you likely have more serious problems. Dunno.

Originally Posted by markopolo

I put a 500W load on the system as part of a test and was working near the fuse and felt the heat coming off it. The cause was a washer underneath.

It is a good idea to do the "heat test" on all your high-current connections and wires. It is a quick and dirty way to detect all kinds of defects, including bad crimps.

[VanFan]

Originally Posted by peteco

Occasionally I see mention of a terminal fuse. Sounds like a good thing to have. If all the circuits already have their own fuse or breaker, then the terminal fuse is primarily covering a short to ground between the battery and the first fuse/breaker in the line, which is either a 30 or a 50 amp in my Roadtrek 210. The terminal fuse would also be a backup in case one of the others failed closed. I would think the terminal fuse should be upsized somewhat so the other fuses or circuit breakers activate first. Am I missing anything here and any thoughts on sizing?

I did this on my last yacht. But instead of a fuse I used a Blue Seas surface mounted circuit breaker. More expensive, but a lot easier to deal with while a boat is pitching and yawing under weigh or at anchor. That's not usually a problem with an RV of course. But it's also a lot easier to spot the problem if it trips, as opposed to pulling a fuse. Plus you don't have to keep spare fuses on hand. Here's their 50 amp version (they have other sizes):

https://www.bluesea.com/products/703...anel_Mount_50A

[Rodneyhelfrich]

If a dedicated alternator fuse at the battery blows, it is likely there is a direct short to ground that the battery is feeding. Ya just saved the coach from fire.

[VanFan]

Originally Posted by avanti

They are also useful if you want to put a fuse on a second=alternator output as well Whether this is a good idea is a different question. This issue is that if it blows, it will remove the load from the alternator, which will likely damage the alternator. OTOH, if it blows, you likely have more serious problems.

Yep. Been there done that. A technician left the lock washer off a 300 amp fuse and road vibration backed the nut off enough to break the circuit. Moral of that story is to always use the lock washers that come with large capacity fuses, and check the torque on those nuts from time to time. (And yes, the washer always goes on top, between the nut and the fuse contact, never under the contact.)

Also, Larry at Starlight Solar turned me on to this this gizmo, which he swears will save the alternator if it happens again:

https://sterling-power.com/products/...tection-device

They're dead simple to install, and you can buy them stateside from Starlight:

https://www.starlightsolar.com/starl...lar/index.html

[dicktill]

Originally Posted by avanti

Yeah, MRBF fuses are the best.

They are also useful if you want to put a fuse on a second=alternator output as well Whether this is a good idea is a different question. This issue is that if it blows, it will remove the load from the alternator, which will likely damage the alternator. OTOH, if it blows, you likely have more serious problems. Dunno.

Originally Posted by VanFan

Yep. Been there done that. A technician left the lock washer off a 300 amp fuse and road vibration backed the nut off enough to break the circuit. Moral of that story is to always use the lock washers that come with large capacity fuses, and check the torque on those nuts from time to time. (And yes, the washer always goes on top, between the nut and the fuse contact, never under the contact.)

Also, Larry at Starlight Solar turned me on to this this gizmo, which he swears will save the alternator if it happens again:

https://sterling-power.com/products/alternator-open-circuit-protection-device

They're dead simple to install, and you can buy them stateside from Starlight:

https://www.starlightsolar.com/starl...lar/index.html

The Sterling Power device sounds good, but it is a tad pricey, albeit much cheaper than a new alternator. I have installed a Balmar TSP-12 Spike protector on my Nations alternator. However, it doesn't show that it was tripped and possibly burned out?????

The problem as VanFan stated is a nut coming loose, and this could negate the advantage of either of these protectors. On all these critical locations I use self-locking (Nylok) flange nuts from McMaster Carr:

5/16-18: 93298A120
3/8-16: 93298A130
8x1.25mm: 92461A400

The flange usually eliminated the need for a washer.

[Hatteras Jim]

I have been using these re-settable circuit breakers for awhile now and have had good success with them. I used them in several van/truck conversions for the local rescue squad and have also used them in my own Sprinter conversion. Relatively in-expensive and when working on the downstream side it's very easy to isolate the circuits without disconnecting the battery. Available from 25 amps to 150 with another (and slightly more expensive) water resistant model from 50 to 200 amps.


The biggest drawback (IMO), is the 1/4 - 20 bolts used for connecting the terminals. OK at low amps; but, if you need to run 4 ga wire or larger to handle the load you are using, the 1/4" bolts seem a little inadequate. However; having said that, I never had a problem using them with the larger wire.


https://powerwerx.com/bussmann-reset...ircuit-breaker

[Thevon]

For all the non electrical engineers that read this forum, do you just mount these on top of the positive battery terminals? If so, would I need one on both House batteries? Even a dumber question, wouldn’t the fuses already in the RT protect the 12volt system or do these fuses keep something from melting down underneath? I hate to seem so elementary but I’m trying to make sure I’m understanding the systems. I added a second battery this spring to the little compartment in front of the rear passenger tire, but didn’t know I need a fuse on top of it.

Thanks

Greg, 2006 190P

[Deano]

I was concerned about the possibility of the cables from the coach batteries shorting out. As I was converting from one 12 volt to a pair of CG 6 volts, I added an inline 100 amp fuse.

[avanti]

Originally Posted by Thevon

For all the non electrical engineers that read this forum, do you just mount these on top of the positive battery terminals? If so, would I need one on both House batteries? Even a dumber question, wouldn’t the fuses already in the RT protect the 12volt system or do these fuses keep something from melting down underneath?

Any wire run between the battery positive and the first fuse is unprotected. The beauty of MRBF fuses is that they can be mounted directly on the battery positive, so essentially everything is protected. I have one on each battery. Not that expensive.

[Bud]

Originally Posted by avanti

Any wire run between the battery positive and the first fuse is unprotected. The beauty of MRBF fuses is that they can be mounted directly on the battery positive, so essentially everything is protected. I have one on each battery. Not that expensive.

And Hey, thanks to avanti I'm maybe, probably the only 05/04 roadtrek 190 that has fused batteries!

Bud