Log In | Register
Skip to main content
Topic: Master DC Circuit Breaker sizing (Read 181 times) previous topic - next topic
0 Members and 2 Guests are viewing this topic.
Master DC Circuit Breaker sizing
I have searching the forum to learn about adding batteries in parallel. I see a wide variation in circuit breaker sizes (amps) mentioned. Does someone know the true sizes that the factory installed over the years, and the reasoning behind any changes?
2013 27’ Mid-Bath
2005 Honda CR-V
Re: Master DC Circuit Breaker sizing
Reply #1 –
All the DC circuit breakers are sized to the wiring size used.  My 2016 MB has the 75 amp parallax converter so LD upsized those wires to and from the converter to allow the higher charging amps. The CBs were also upsized to match the wire gauge.  My drawing notes the changes, the manual was not updated to match what was on my MB.
2016 Mid Bath
Re: Master DC Circuit Breaker sizing
Reply #2 –
Wow your manual is much better than my 1988 MB Manual!
These wire sizing's are based on several standards.
all standard look at insulation type and service temperature.

NEC looks at 80% of the wire capacity.  This is also for solar.

SAE and Marine standards also looks at wire location (Engine Compartment or chassis), and
Critical circuits 3% voltage Drop.
Non-Critical circuits 10% voltage Drop.
.


In rush ampacity eventually becomes the controlling factor.  hence the reason for soft starts and VFD's.
Rodney
1988 Mid Bath
Re: Master DC Circuit Breaker sizing
Reply #3 –
Quote from: Keith S  - 
I have searching the forum to learn about adding batteries in parallel. I see a wide variation in circuit breaker sizes (amps) mentioned. Does someone know the true sizes that the factory installed over the years, and the reasoning behind any changes?
Since adding batteries in parallel, are these to be added to the stock batteries, similar chemistry, or are you replacing them with Lithium? If adding, how far away and other installation details?

Steve
2004 FL
2013 Honda Fit
 
Re: Master DC Circuit Breaker sizing
Reply #4 –
I have two 2-year-old Battleborn 100 Ah LiFePO batteries, and am adding two more. The four will be located very close together (in the mid-bath floor plan). I don’t think that the battery circuit breaker size depends on the batteries, only on the wiring size to the charger and inverter.
2013 27’ Mid-Bath
2005 Honda CR-V
Re: Master DC Circuit Breaker sizing
Reply #5 –
Hi Keith.  Where will the four batteries be placed in your MB?
Greg & Victoria
2017 Mid-Bath  “Nocona” towing a manual 2015 Forester
Previously a 1985 TK
SKP #61264
Re: Master DC Circuit Breaker sizing
Reply #6 –
Quote from: Keith S  - 
I have two 2-year-old Battleborn 100 Ah LiFePO batteries, and am adding two more. The four will be located very close together (in the mid-bath floor plan). I don’t think that the battery circuit breaker size depends on the batteries, only on the wiring size to the charger and inverter.
If the batteries are close together, you should not need additional circuit breakers. What you DO need is to preserve equal current flow through all batteries to preserve balance. If you consider all the batteries in a bunch, with all the positives daisy chained and same with the negatives, then the positive input/output should be uniquely from the battery at one end of the chain, and the connection to ground (or battery shunt) at the battery at the other end. The positive and negative jumpers from any battery to the adjacent one should be equal in length and gauge, etc. Introducing a circuit breaker at any point will potentially disturb that balance.

Steve
2004 FL
2013 Honda Fit