Extending existing 8awg with 4awg, do I need multiple breakers?

[daveemac]

I'm upgrading the system in my RV and want to move the battery location while I'm at it. 8awg is already run under the floors, and I don't want to tear everything apart, so I'm planning to extend the existing wires to their new location. I'll be following Will's schematic for "400 Watt Solar Package w/Alternator Charging", and using his recommended breaker and wiring recommendations: https://www.mobile-solarpower.com/simplified-400-watt-fewer-wires-and-alternator-charging.html

The original system has two 8awg wires I need to extend: one goes to my DC fusebox (small loads, way under 30A), and one carries current from my alternator (10A max, limited by Kisae DMT1250). In the original system they each pass through a 30a breaker before connecting to the battery. I could add the 4awg wires before or after the 30a breaker, and I'm not sure which way is best.

Original roundtrip with the existing 8awg is about 12', and 3' will be removed when I add 6' of 4awg. So when completed it'll be about 9' of 8awg and 6' of 4awg. 100AH lithium battery w/100A BMS...and I may add another identical battery later to facilitate a 2000W inverter. (Currently I'm relying on the inverter from my Bluetti AC200MAX).

So: do I need to keep the 30a breakers to protect the 8awg downstream, or will the larger breakers closer to the battery suffice?

Thanks!

 

[Firewalker30091985]

I have for my Batteries 250AWG in Germany is it over 120mm² so i have connected 2 blocks of Lifepo4 with Breaker and 1 fuse with 300Amps;
both Blocks have 22Kwh Capacity at 48V so i have near 200Amps at Consumption Max..

Loading current is max 200Amps.

 

[daveemac]

Thank you for your reply. However, I'm sufficiently newbie that I don't understand it as an answer to my question:

If I have higher amperage breakers protecting my 4awg close to the battery do I need lower amperage breakers downstream to protect the 8awg?

 

[Cdkipp]

I am not sure I have this straight or whether it will work for you. In my system I increased the wire size between the battery and the DC fuse box and then left those fuses as they were. However I also installed larger T-fuses upstream with my new lithium batteries and inverter. There I increased both the wire size and the fuse size.

 

[MrThisIsME]

Thank you for your reply. However, I'm sufficiently newbie that I don't understand it as an answer to my question:

If I have higher amperage breakers protecting my 4awg close to the battery do I need lower amperage breakers downstream to protect the 8awg?

If the max current as dictated by your breaker is 30amps, you are fine running either 4awg or 8awg downstream. Either cable will carry 30amps for a reasonable distance safely

I have to ask, why only a 10amps from the charger? It appears to be a 50amp DC-DC charger ( I assume there is an adjustment to get it down to 10amps). This seems like a waste of almost free power coming off the alternator. Take advantage of the LiPo charge capacity and crank it up! Even more so if you plan to add a second battery.

 

[camelCase]

If you have multiple wires sizes on a single run, you would fuse it to protect the smallest wire. You should keep the 30a fuse.

 

[daveemac]

Thanks for all the replies, got it

I'm limiting my alternator current

If the max current as dictated by your breaker is 30amps, you are fine running either 4awg or 8awg downstream. Either cable will carry 30amps for a reasonable distance safely

I have to ask, why only a 10amps from the charger? It appears to be a 50amp DC-DC charger ( I assume there is an adjustment to get it down to 10amps). This seems like a waste of almost free power coming off the alternator. Take advantage of the LiPo charge capacity and crank it up! Even more so if you plan to add a second battery.

The generator is only rated for 60 amps. How much current do you think I can safely pull from it w/o harming starter battery operation?

 

[camelCase]

60 amps is low by modern standards so 10 amps is a good conservative number in my opinion.

You may be able to upgrade your alternator, though. What type of vehicle is your RV based on?

 

[daveemac]

60 amps is low by modern standards so 10 amps is a good conservative number in my opinion.

You may be able to upgrade your alternator, though. What type of vehicle is your RV based on?

Thanks. It's a 1990 Toyota pickup, 6cyl 3.0. There are lots of upgraded alternator options. How much capacity would you recommend?

 

[camelCase]

Can you ever have too much solar or alternator power? As a general rule of thumb, you shouldn't pull more than half the rated amperage from the alternator for an extended period of time to avoid cooking it. A third of rated capacity is even safer.

If you wanted to use the full 30 amps from your DC-DC charger, a 100 amp alternator would be the minimum I would want to see.

 

[daveemac]

Can you ever have too much solar or alternator power? As a general rule of thumb, you shouldn't pull more than half the rated amperage from the alternator for an extended period of time to avoid cooking it. A third of rated capacity is even safer.

If you wanted to use the full 30 amps from your DC-DC charger, a 100 amp alternator would be the minimum I would want to see.

Thanks, that's very helpful. I'll start w/20 and then maybe upgrade my alternator down the road...

My charger can do 50 btw....and there are 160a alternators for my truck, hmmm

 

[camelCase]

If you upgrade the alternator, be sure to upgrade the wiring to handle the extra current.

https://jlaudio.zendesk.com/hc/en-us/articles/204374080-The-Big-3-Wiring-Upgrade

 

[daveemac]

If you upgrade the alternator, be sure to upgrade the wiring to handle the extra current.

https://jlaudio.zendesk.com/hc/en-us/articles/204374080-The-Big-3-Wiring-Upgrade

Thanks for this--I'll make these upgrades if I update my alternator.

 

[MrThisIsME]

Thanks for this--I'll make these upgrades if I update my alternator.

I think you will not be impressed with the 10amps you pull from the alternator. I fear you might leave the truck running (read expensive gas) to make up for the low amps.

Not sure of your entire goal here, but a quick search seems to produce a lot of results for upgrades. Saw a couple of 120amp alternators for $150. Compare the output of that $150 (granted gas is burned) to a solar panel and it would be a no brainer to me.

As other's have mentioned, upgrade the cabling if you do swap.

 

[SparkyJJO]

That is only a 150HP engine (at 4800 RPM). I have no personal experience with it, but that is not very much at all. Just be aware an alternator upgrade will pull more power from the engine so depending on what you're doing at the time, it may impact driving performance. How much, I don't know. At least being a V6 it reaches its peak HP at a lower RPM than some 4 cylinder engines and probably better torque.

Our 2013 Civic only has 140HP (at 6500 RPM) and running the AC has a noticeable drag to the point where if I go to merge on a very busy highway with a short onramp I'll turn off the AC to help it get scooting a little quicker.