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Posts: 5290 		Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Topic: ouR escaPOD mods
    Posted: 27 Mar 2020 at 5:27pm
Originally posted by StephenH

No, it was not tripping immediately. Once it started tripping though, the intervals between reset and tripping were growing shorter and with lower amperage readings on my meter. That is why I concluded that the breaker was a piece of junk.

Yep I agree. Hope the replacement works better.
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Posts: 6417 		Post Options Post Options   Quote StephenH Quote  Post ReplyReply Direct Link To This Post Posted: 27 Mar 2020 at 4:38pm
No, it was not tripping immediately. Once it started tripping though, the intervals between reset and tripping were growing shorter and with lower amperage readings on my meter. That is why I concluded that the breaker was a piece of junk.
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Posts: 5290 		Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: 27 Mar 2020 at 6:51am
Did your previous breaker tend to trip when you first connected your charger? High inrush currents could be the problem. those are typical with devices like chargers (ones with large magnetic coils and/or large capacitors in them). A breaker with a longer time delay before tripping would help with that. That would typically be described as a "thermal" breaker as opposed to a "magnetic" or "thermal/magnetic" breaker with a short time delay that will trip very quickly rather than ride out an inrush current for a few seconds. 
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Posts: 6417 		Post Options Post Options   Quote StephenH Quote  Post ReplyReply Direct Link To This Post Posted: 26 Mar 2020 at 3:34pm
Thanks. The 60A breaker next to the battery was the one that went bad. I'm thinking a fuse might work better as I have a separate cut-off switch already and won't ever use the breaker for that purpose anyway.

Edit: Looking at the various ones on Amazon and knowing the wire I put in is capable of the 100A, I opted for an 80A circuit breaker. This one has a different design, so I hope it will work better than the 60A one that failed.
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Posts: 5290 		Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: 26 Mar 2020 at 2:41pm
Those specs say that you should never pull more the 70A from the battery continuously or 100A for 10 secs. They don't say that the battery is self limiting to that, I don't think it is. So, if you short that battery out it can produce hundreds of amps, just like a lead acid batt, maybe more. Bad for the battery and bad for your system wiring. I'd highly suggest adding a bolt on fuse (60A should work if your charger is 50A) at the + battery terminal. Shouldn't have the problem your cb had but carry a spare like you would for any other fuse. 

The condition I'd be worried about is if I shut off the engine and then I or someone turned the ignition back  on and accidentally left it on, I wouldn't want the dc/dc to be on. With one lead acid battery connected in parallel to another its not a big deal if that happens, they will slowly come down together, but if your trailer batt is not fully charged the dc/dc will happily try to send 20A to your trailer battery until your start batt is dead. If your TV cuts off 12V to the trailer under that condition you could just run +12V from the 7 way connector to both the power terminal and the control terminal. If its always part of your camp setup checklist to disconnect the 7 way then it would only be a problem during a rest or restaurant stop (assuming we can get back to eating at restaurants again someday). Embarrassed
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Posts: 6417 		Post Options Post Options   Quote StephenH Quote  Post ReplyReply Direct Link To This Post Posted: 26 Mar 2020 at 12:57pm
Originally posted by offgrid

Yeah a dc/dc converter is the way to go. Li batteries have a much narrower charging voltage window than lead acid batts so need a more stable voltage to charge properly. The one you're getting should work fine. Note that it needs a terminal to be brought to 12V to turn on. That is normally connected to your ignition so if you ever leave your ignition on with the engine off you could discharge your start battery pretty quickly. I'd be tempted to put a switch under my dash in that line so I could turn the dc dc converter on and off manually if I wanted to. 
That is what I may need to do. The Frontier seems to cut off power to the 7-way connector when the engine is off and the lights time-out. If so, I may be able to tap into that for the power signal. Otherwise, I will have to figure out where I can place a switch for this purpose. Most of the wiring diagrams I have seen assume the unit will be installed in a motor home, not a trailer. Putting it in the RPod adds complexity to the installation, but I'll figure out something. As for the battery, I will be checking the specs. I put in heavy enough wiring to handle the 100A rating of the battery. Here are some quick specs from the Amazon listing:

Battery Specifications

  • Nominal Voltage: 12.8v
  • Charging Voltage: 14.4±0.2v
  • Rated Capacity : 100Ah (0.2C, 25°C)
  • Terminal Type: F12/ M8
  • Dimensions (L x W x H): 13 x 6.8 x 8.4 (H + Terminal: 9.3) Inch
  • Weight: 22.6lbs
  • Max. Continue Discharge Current: 70A
  • Max. Permanent Discharge Current: 100A 10Sec.
  • Max. Continue Charge Current: 50A
  • Operating Temperature: Discharging: -4°F to 140°F; Charging: 32°F to 140°F
StephenH
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Posts: 302 		Post Options Post Options   Quote Subzilla Quote  Post ReplyReply Direct Link To This Post Posted: 26 Mar 2020 at 10:42am
Thanks for the thorough explanation Offgrid. Makes total sense. Mark
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Posts: 5290 		Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: 26 Mar 2020 at 10:30am
I think there is still some confusion on the purpose of fuses/circuit breakers in an electrical system. 

The purpose of fuses and CB's is to protect the system wires, not the battery, charger, or solar module. Same in your house, your panel cbs are there for the wires in your walls. The devices you hang on your circuits are supposed to be self protected, which in theory is assured because they carry UL listings.  

The battery can produce tons of current. As a thought experiment, place an imaginary short circuit in your wiring at different places in your system and see if one of your circuit breakers or fuses protects the wiring between your battery and the location of the short. If it doesn't then if you got an actual short at that location you could melt the wire insulation and have a fire, so you need to add a fuse or circuit breaker that protects that wiring from that. 

I haven't heard of a BMS that provides overcurrent protection. They are there to provide over and under voltage protection and cell voltage balancing. If the BMS did provide overcurrent protection that would be identified in the specs along with a current trip level.

Yeah a dc/dc converter is the way to go. Li batteries have a much narrower charging voltage window than lead acid batts so need a more stable voltage to charge properly. The one you're getting should work fine. Note that it needs a terminal to be brought to 12V to turn on. That is normally connected to your ignition so if you ever leave your ignition on with the engine off you could discharge your start battery pretty quickly. I'd be tempted to put a switch under my dash in that line so I could turn the dc dc converter on and off manually if I wanted to. 
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Posts: 6417 		Post Options Post Options   Quote StephenH Quote  Post ReplyReply Direct Link To This Post Posted: 26 Mar 2020 at 9:36am
The fuse was placed near the battery and was on the line that went between the converter and the battery. Since the converter is on a breaker and since I have a 10A fuse now for the solar, I likely don't need the breaker that was near the battery. The BMS should also help protect the battery. I've found that the Frontier does not seem to be charging the battery so I ordered a Renogy DC to DC charger which I will install to be able to have the battery fully charged while we are traveling. This is the one I ordered: http://www.renogy.com/12v-dc-to-dc-on-board-battery-charger/ . The 20A model (DCC1212-20) is the one.
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ouR escaPOD mods
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Posts: 5290 		Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: 26 Mar 2020 at 7:42am
Originally posted by StephenH

I just installed one in the extension cable that I made. It is going to be closer to the panel when it is in use. 

Sorry your breaker failed. Unless you were running a 6 gauge extension cord a 60A breaker wouldn't protect it anyway.  10A will be fine for that module. 

Just to be clear though, fuses and circuit breakers are there to protect from excessive currents coming from the source so they should be placed as close as possible to the source of the current. If you place your 10A fuse downstream from the battery then the wiring between the battery and the fuse is not protected. If you got a fault in that section of wire the fuse wouldn't know about the high current so it wouldn't clear the fault. You might consider moving the 10A fuse to the battery or adding a bolt on fuse right on the battery + terminal.
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