[Three6ty]

To all you Electrics experts out there, can you take a look and see if my diagram looks good.
Please offer any suggestions where you think it might be overkill or the opposite.
My DC load will be a 12V Isotherm Fridge, 10 12v LED lights, 3 USB chargers, Maxxair Fan.
My AC load will be a small Toshiba 700 watt Microwave, Keurig coffee maker, and possibly a single burner induction cooktop. ( not all running at the same time)

I copied this diagram off someone else and put in my relevant electrical components. Please give me some feedback .
Thanks in advance

 

[GaryBIS]

Looks good to me.

The 70 amp fuse you show between the service battery and DC to DC converter should be positioned as close to the service battery as possible.
Likewise the 60 amp fuse should be placed as close to the house battery as possible.
That is, fuses should be as close to the power source as possible.

Make sure that the charge controller you are using has a high enough input voltage to handle your 305 watt panel. Lookup the Voc voltage of the PV panel and make sure its lower than the max voltage the solar controller can handle.

Gary

 

[Three6ty]

yea im' pretty sure i'm good here with the solar panel. here is the pic off the back of it.

 

[Three6ty]

Gary - For the 60amp fuse you mention above (close tot he house battery), I have it going in after the Charge controller /dc/dc charger and before the busbar. I have a 250amp fuse/breaker right next to the house battery. I will have the 250amp breaker/fuse close the the house battery.
Anything you would change there?

 

[mjm6]

So I honestly don't know how big of a deal this is, but most of the solar charge controllers will tell you that you should not have the solar hooked up to the controller if the battery is not connected, that it will damage the SCC.

You have a disconnect for the battery, and you have a breaker for the solar input, but there is nothing that ensures that the solar is disconnected when the battery is disconnected.

I specifically asked a manufacturer about this and they were somewhat equivocal about whether this is an issue or not. I'm going to treat it like it is an issue and I will have a disconnect for the battery and the solar in a single switch (two pole switch). That will ensure that if I go to throw the battery out and forget to disconnect the solar, they will both be disconnected at least at the same time and not have solar going into the SCC without a battery on the other end.

 

[GaryBIS]

Hi,
The DMT1250 lists its allowed voltage input range for its PV panel as 10.5 to 32 volts, and the Voc on the PV panel is listed as 40 Volts -- so, this seems like a problem to me. The actual voltage of the PV panel on very cold days will be even higher than the the Voc they quote, which is for 25C, and it goes up a little for each degree C colder than that.
An example calc here: Calculating Max PV Voltage is Not Scary - Sunny. Der SMA Corporate Blog

Not sure what the DMT does when its input voltage is exceeded -- it may just shut down and restart when the voltage drops back down, in which case you would be OK. But if it damages the DMT, that would be a problem. I would at least call up Kisae and ask them.

On the 60 amp fuse, I'd put it in right at the busbar. The reason for getting it as close as possible to the current source (house battery) is that if there is a short to ground on this wire, then unless the fuse is closer to the battery than the short, the fuse does no good, and you have a direct short to ground and lots of fireworks.

If the positive busbar is right at the house battery, the 250 amp fuse is not really required as all of the wires coming out of the busbar are fused (as they should be) -- at least, that would be my interpretation of the ABYC (marine) code. Others may disagree with this??
I guess it could be said that it does no harm being there, but on the other hand, its just another component that could fail at some point -- I'm a believer in simple is good

Gary

 

[Somebodyelse]

I'd agree that the 250a fuse is unnecessary if the busbar is right there and every other line is fused right after the busbar. If there's a distance between batteries and busbar, I'd fuse it as close to the house bank as possible. Otherwise, that will almost definitely not be the fuse to trip as a smaller fuse would blow first if there was a fault. If the distance between each smaller fuse is roughly the same as the distance would be to the large fuse, nothing extra is really being protected.

I like mjm6's idea of a double pole, single throw cutoff for the solar and batteries. Especially if still paired with a resettable breaker or isolated cutoff for the solar, if you just want to toggle it off and leave the batteries. It's not necessary, but takes the order of operations and memory components out of the equation. Clever.

 

[mjm6]

Not sure, but I think the code calls for a fuse within 7" of the battery, and in the case of the bus bar, the sum of the fuses connected to it are greater than 250A, so I think you should have one between the bus bar and the battery.

It may be possible to have the fuse right near the bus bar to satisfy that, but something tells me that there shouldn't be any other paths from the battery to any other device before that main fuse is in the system. Without it, you could have a cascade of fuses blowing before the system shuts down.

Lastly, the fusing on the inverter/charger looks small to me... I just checked and it looks like Renogy recommends a 200A fuse there, not 175A. I suspect the difference has to do with surge capability in the device (or possibly safety multipliers for the line), and while 2000W into 12A is 166A, 175A doesn't meet the generally recommended safety margins for the line, which normally is considered 120%. Renogy says 200A, and I have seen others say 250A for a 2000W inverter/charger.

I think when they go larger than 200A, they are accommodating the surge capability of the inverter. For example, if you take the 6000W surge the Renogy can handle into 12V, you get 500A. Presumably, you won't see that often (ever), but if it does go anywhere close to that, you will blow that 175A fuse really fast.

My recommendation is to wire it for a reasonable wattage and at least follow the minimum amperage recommendations of the manufacturer, even if you don't think you will be loading it up fully. A microwave has very high inrush, and could be coming close to that max, (or higher) for a brief amount of time. That 700W microwave will use 1000W total (in addition to the 700W that goes to the micro coils), and the inrush is often considered to be about 3x the unit, so that would be in the range of 2100W to 300W, but only for a brief period of time.

 

[83Grumman]

The DMT1250 lists its allowed voltage input range for its PV panel as 10.5 to 32 volts, and the Voc on the PV panel is listed as 40 Volts -- so, this seems like a problem to me. The actual voltage of the PV panel on very cold days will be even higher than the the Voc they quote, which is for 25C, and it goes up a little for each degree C colder than that.
An example calc here: Calculating Max PV Voltage is Not Scary - Sunny. Der SMA Corporate Blog

Not sure what the DMT does when its input voltage is exceeded -- it may just shut down and restart when the voltage drops back down, in which case you would be OK. But if it damages the DMT, that would be a problem. I would at least call up Kisae and ask them.

This is from the Kisae owners manual. It looks like it will shutdown if you exceed 45.0V

Abso DC to DC Battery Charger
12V 30A (DMT1230) 12V 50A (DMT1250) Owner’s Manual

DC Input (CH2 – PV Solar Array/ Panel)
PV Input Voltage Range 14.5 - 45V
PV Input Under Voltage Shutdown < 14.5V
PV Input Under Voltage Recovery 15.0V
PV Input Over Voltage Shutdown > 45.0V
PV Input Over Voltage Recovery ≤ 44.0V
PV Charging Mechanism MPPT type (approx. 97% efficiency)
Maximum Input 500W (*Note)
*Note: The recommended maximum solar wattage input for the Charger is 500w. You can however “overdrive” the MPPT controller. Please note that doing this is partially an economic decision. You can install more power than the controller can use and this will contribute to better power availability. KISAE suggests a total maximum overdrive of 20% (total 600w). On cloudy (or intermittent sunny) days there will be little or no power shaving and the extra power will serve the battery well with more energy harvest earlier and later in the day.

 

[travelvanvan]

To all you Electrics experts out there, can you take a look and see if my diagram looks good.
Please offer any suggestions where you think it might be overkill or the opposite.
My DC load will be a 12V Isotherm Fridge, 10 12v LED lights, 3 USB chargers,
My AC load will be a small Toshiba 700 watt Microwave, Keurig coffee maker, and possibly a single burner induction cooktop. ( not all running at the same time)

I copied this diagram off someone else and put in my relevant electrical components. Please give me some feedback .
Thanks in advance View attachment 68610

What is the sustained output (amps) of your LiFePO4 battery? Is it a single 275Ah battery or a battery bank that has multiple batteries that add up to 275Ah?

I ask this because your microwave, if like mine, will draw 100A alone. And if it's a single battery, it may not be able to sustain more than 100A. If it's a battery bank with multiple batteries in parallel, then it is more likely you are ok.

Many 100Ah batteries can sustain 100 amps output, but it doesn't necessarily follow that a single 275Ah battery can output 275 amps. The limit is determined by the battery's controller board, often capped at 100A, regardless of the battery's capacity.

In my prototype build, because I was taking a leap of faith on Li technology and it's expensive, I only had a single battery, rated 100A output. This worked with a similar set of requirements to you. But it was borderline because of the microwave. There could be scenarios in which the battery's output (hard max of 105A) could be inadvertently exceeded: microwave at 100A, fridge at 4A, LED lights 2A, laptop and camera chargers 10A, etc.--and now it's way over. I was always careful, but I could have made a mistake. I've addressed it with more batteries in parallel, so my bank's sustained output is now much higher.

 

[GaryBIS]

Not sure, but I think the code calls for a fuse within 7" of the battery, and in the case of the bus bar, the sum of the fuses connected to it are greater than 250A, so I think you should have one between the bus bar and the battery.

It may be possible to have the fuse right near the bus bar to satisfy that, but something tells me that there shouldn't be any other paths from the battery to any other device before that main fuse is in the system. Without it, you could have a cascade of fuses blowing before the system shuts down.
....

Hi,
Not at all saying you are wrong about this -- I just don't know.

But, how do you get a cascade of fuses blowing?

My system has no busbars, the wires to the DC panel, inverter/charger, etc. just come directly into the battery terminals. Each one of these lines has its own fuse that is close to the battery. If you think of the busbar as just an extension of the battery terminal to make it easier to hook up all the wires, then why is the that large master fuse needed?
On the other hand in house wiring its common to have a main breaker followed by lots of branch circuit breakers.

Gary

 

[Three6ty]

Thanks guys for the responses. Great stuff to think about.
I have 2 Batteries wired in parallel. Each are 138Ah, so roughly 275Ah at 12V

 

[mjm6]

Hi,
Not at all saying you are wrong about this -- I just don't know.

But, how do you get a cascade of fuses blowing?

My system has no busbars, the wires to the DC panel, inverter/charger, etc. just come directly into the battery terminals. Each one of these lines has its own fuse that is close to the battery. If you think of the busbar as just an extension of the battery terminal to make it easier to hook up all the wires, then why is the that large master fuse needed?
On the other hand in house wiring its common to have a main breaker followed by lots of branch circuit breakers.

Gary

Yes, that's why the main breaker is on a house panel. It acts as a service disconnect, and also protects the loads downstream from a service that has run out of control.

I'm not suggesting that it is likely to occur, maybe it will never happen, but if a battery bank goes haywire, the main fuse could save all the wiring downstream. I figure it's a small price to pay for some protection. I have one of the battery terminal fuse blocks to use for this as I develop my build. I hope to be into real electrical work by the end of the month.

 

[Somebodyelse]

Fair warning: a lot of the post following the first paragraph is unnecessary background information.

FWIW, Gary's depiction of the bus bar just being an extension of the battery terminal is really good phrasing. If you are extending those terminals any significant distance or through any barriers or if the busbars have a lower amp rating than your batteries can provide, it should definitely be fused to the lower amount of either the wire rating or busbar rating. If you're really just shifting the connection point slightly, it doesn't make a lot of sense to protect such a short run (as long as everything past is correctly protected). It's more logistics, if you're not really moving the first possible point of failure then additional devices are just that(additional devices).

The main breaker on an electrical service cabinet is to protect the bussing in the cabinet. Different cabinets will have different ratings and different quality(size) of hardware. The main breaker is sized to prevent melting lower rated hardware if someone were to try to use the full capacity of every circuit all at once. I do not know this theory of cascading blown fuses.

Electricity doesn't get 'forced' anywhere from the source, it's more 'requested'. Generally circuits are not expected to use the full capacity available. The size of the fuse it not related to the equipment, but to the size of the wire so it doesn't melt. The draw is then what the device needs to operate. When operating correctly, devices don't complete a circuit unless they are being used.

Most common, a circuit trips because of a fault or short which cuts the device out of the circuit and connects the hot (or positive) directly to the ground or neutral (or negative). Occasionally, a large surge will imitate a short circuit. The most sensitive breaker will blow first and the 'problem' will 'disappear'. I can't think of, have heard of, or have seen a situation where a fault in a circuit would blow the main. If no additional overcurrent devices were used, I would imagine the possibility of the building burning down long before the main breaker tripped for the first time. This has occurred in the houses with screw in fuses that people replace with coins (wasn't an uncommon practice, was incredibly dangerous), but that style breaker box is uncommon now.

 

[RV8R]

This has occurred in the houses with screw in fuses that people replace with coins (wasn't an uncommon practice, was incredibly dangerous), but that style breaker box is uncommon now.

What caused the fire?

Literally a 5 cent fuse😳

 

[travelvanvan]

What caused the fire?

Literally a 5 cent fuse😳

Perhaps in some cases, it was a situation where a spare fuse wasn't available (e.g. ran out). Maybe a forgotten jury rig? That's why a box of spare fuses (at least 1 of every size that's in use) is a good idea.

 

[RV8R]

Perhaps in some cases, it was a situation where a spare fuse wasn't available (e.g. ran out). Maybe a forgotten jury rig? That's why a box of spare fuses (at least 1 of every size that's in use) is a good idea.

Spare fuses 😳

So,,,October 2019 we were down in LA with the van. We were "camping" in Orange County hooked up to shore power and I blew the fuse from my + bus bar to the DC panel (I was able to diagnose it without looking at it - the magic of "design/build", switches, a battery monitor, and usb chargers with voltage indicators). I came to the diagnostic conclusion (correctly apparently) that I "sized" my fuse to my DC panel @ 30 amps which is correct for the panel, but wrong for the charger which can produce 45 amps going the other way. Everything still worked providing we were on shore power 😁

Guess what; I was brilliant enough not to have any "specialty" Blue Sea spare fuses with me. We drove all over Orange County and eventually to Long Beach "West Marine" and purchased a replacement fuse

And a couple of "Spare Fuses". We have lots of spare fuses now.

 

[Three6ty]

Thank you all for your help here. I just finished my Electrical/Solar install. Not perfect but It turned out pretty good. There will be a panel that will go over it hiding everything from the garage so no one will really see any of it, but I wanted it to look clean. Breakers and Disconnect will be left open for quick access if needed.