# Battery Packs and fuse protection?



## noela (May 22, 2008)

I have two projects coming up that will require unusual battery configurations. I will, in all probability make my own battery packs, they will be NiMh. One will be 12 vdc, and the other may need to be 19.2 vdc. I will need to protect these batteries with resettable fuses, if possible. Can anybody suggest a method for doing this? Is there a formula for determining the proper voltage/current rating for such devices?
Thank you.


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## Greg Elmassian (Jan 3, 2008)

Sure, how much current will your loco draw worst case? You already know the voltage. 

If you want resettable fuses, you mean self-resetting or manually reset? You of course don't mean a REAL fuse, but a form of circuit breaker. Or were you thinking of a "polyswitch" which is a current limiting device, does not shut off entirely. 

Not giving you a hard time, but you want to figure out what type of protection you want, and also what you are willing to spend. 

If it was me, and I had room for them, and the $$, I'd use a resettable circuit breaker with the reset button on the bottom of the loco. The self resetting ones seem to keep trying to reset but the short may still exist. I don't like the polyfuses, they lose too much current and are too slow in my personal opinion, but that's just me, they work fine for others, and are better than nothing. 

Greg


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## Tom Parkins (Jan 2, 2008)

Try the automotive or RV section of your local auto supply house. I have a trailing battery car that uses 19.2 v nominal max voltage. I put a 6 amp glass cylinder automobile fuse in series going out the power car. It's originally designed for 12 volts, but remember fuses are current sensitive. I typically only run double header with RS3/GP9 and 20-25 car trains on a 2% grade. The 6 amps seems fine, though I have blown a few. They are easily replaced in the battery car. It's cheap. I could probably go with a 10 amp fuse and almost never blow one, but this is safe. I am using an Aristo 27 MHz trackside in the battery car. It too is fused with a 10 amp fuse. Only time I blew that was when I forgot to shut it off and hit the out-put terminals with the screw driver. 

Bottom line.... Go with a 6 or 10 amp automobile fuse. It's cheap, easy and reliable. 

Tom P


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## Greg Elmassian (Jan 3, 2008)

Tom, I think he was asking for resettable fuses.. on "real" fuses, I would recommend the automotive blade type, they are easier to find, and cheaper. 

Regards, Greg


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## izzy0855 (Sep 30, 2008)

Noel, 

First you need to decide what type of protection you want? Charge or discharge? Charge = 70 or 75 degree thermostat. Discharge = .350, .420 or .475 polyswtch depending on the milliamp draw? 

Rick Isard 
Cordless Renovations, LLC


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## Del Tapparo (Jan 4, 2008)

Posted By izzy0855 on 04 Mar 2011 07:18 PM 
Noel, 

First you need to decide what type of protection you want? Charge or discharge? Charge = 70 or 75 degree thermostat. Discharge = .350, .420 or .475 polyswtch depending on the milliamp draw? 

Rick Isard 
Cordless Renovations, LLC 
I think discharge is the obvious answer. I also assume your dimensionless discharge numbers are amps? Those certainly aren't the only choices. The ones I buy usually come in increments of 1 amp.


I use polyswitches in most of my controls as a "last resort" means of protection, but they are indeed slow to react. A glass fuse is much better, which is what I use in my Battery Conversion Modules. Beware of polyswitch ratings, by the way. Just because it is rated for X amps doesn't necessarily mean you can run at that current draw continuously. I have found you need a larger rating than what you really want, based on my test results.

Likewise, don't assume that two X amp polyswitches connected in parallel will trip at 2X the rating. My testing shows that they will trip at a much lower value. 


For the simple solution, I would just recommend an in-line fuse holder and a glass fuse rated for 5 amps.


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## noela (May 22, 2008)

Thank you for the responses. First of all, please, I don't take personal offense to comments. If I had all of the answers, I wouldn't be here. I am seeking input from those that have experience, and can help me avoid any pitfalls that they may have gone through. When I build power supplies, I use manually resettable circuit breakers, as there is normally room to install them. On battery cars, glass fuses have been used, because they are accessible. In the two projects that I am being asked to do, they will be self contained, and accessing glass fuses, while not impossible if I can figure out how to do it, may not be feasible. Circuit breakers, due to their size (unless there are some smaller ones that I am not familiar with), may be difficult to fit into the spaces that I am working with. I am familiar with the limitations of polyswitches, which is why I bridged this question in the first place. 
As mentioned, my primary concern will be discharge, as the charging circuits will be protected by the chargers themselves. 
I really do appreciate the input from these forums. Under normal circumstances I do purchase and install Rick's batteries, but in the two cases in question, the configuration may actually involve multiple smaller packs to fit inside my projects. Both are custom build units with finite install areas, and I must insure that I can protect the battery before I take them on. 
Thank you again. 

Noel


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## Totalwrecker (Feb 26, 2009)

On my 4-4-0 batt conversion I added an auto blade fuse to the underside of the tender, completely out of sight. All I need do is flip the tender over to see the condition of the fuse. I used the socket half of blade type wire connectors, bent 90 degrees through the floor. The fuse lies along the floor behind the side sills. 
With fuse inserted, I epoxied the sockets in the floor, sealing the holes. I did have to rework the sockets slightly as the blade on the fuse was about 1/32 wider. Made more sense to me to modify the sockets for all fuses than to file all the fuses. 

John


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## Greg Elmassian (Jan 3, 2008)

They do make small, self resetting circuit breakers that fit the socket of a mini blade type auto fuse.










This one by Buss, long time manufacturer. These are real circuit breakers, when they disconnect, they completely disconnect vs. the PTC type (Positive Temperature Coefficient), which is a "polyfuse"/"polyswitch".

Greg


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## noela (May 22, 2008)

Hi Greg,
This looks great. I looked around, but couldn't find anything less than 10 amps. I was hoping for something like 5 amps. Any thoughts?
Thanks again.

Noel


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## Greg Elmassian (Jan 3, 2008)

Yeah, I looked for a while too and nothing under 10, strange. I'll look some more, there HAS to be miniature resettable units somewhere... 

Greg


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## noela (May 22, 2008)

Thank you. Going to ECLSTS?


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## Greg Elmassian (Jan 3, 2008)

Nope, would like to, but I am on the other side of the planet. Probably won't make the convention either, drat. 

Greg


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## Pete Thornton (Jan 2, 2008)

Also check out your marine electrical supply house. My big boat has a ton of 12V circuit breakers that are probably rated for 24V max. The small boat has similar push-button breakers. And they are weather-resistant! Ancor is a big manufacturer of ship electrics: 
http://www.shipstore.com/SS/HTML/anc/anccircuitbreaker.html


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## Greg Elmassian (Jan 3, 2008)

All the marine ones I found were 10 amps and up. 

I'll keep looking. 

Greg


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