Can my 20A charger wiring handle a 30A charger replacement?

[GaylesFaerie]

Hi all, My 12 year old 20A charger died as confirmed on a tech-support call with Pronautic. I would like to upgrade to the 30 amp Pronautic charger that has the same hookups and form factor. My concern is the wire gauge going from the charger to the batteries. There are currently three 10 AWG wires coming off the charger leading to a three battery house bank (90As each) with each inline fused at 30A. I am wondering if the 30 amp charger would be OK with that wiring. I tried using the Blue Seas circuit wizard using very conservative values, and it is suggesting 8 AWG for a 30A circuit which would require re-wiring. That estimate though is just for one wire.

My specific question is: does the charger output 30A on each output wire or split it (10A per wire)? If it splits the current I think l'm Ok with 10AWG for the 3 charger outputs. If not, then I will opt to remain with a 20 amp replacement, so as not to have to rewire. I read the Pronautic manual but couldn't find any references to the output behavior of the 3 DC posts with regard to amp splitting. Responses much appreciated in advance. Gary

 

[Submariner]

Hi all, My 12 year old 20A charger died as confirmed on a tech-support call with Pronautic. I would like to upgrade to the 30 amp Pronautic charger that has the same hookups and form factor. My concern is the wire gauge going from the charger to the batteries. There are currently three 10 AWG wires coming off the charger leading to a three battery house bank (90As each) with each inline fused at 30A. I am wondering if the 30 amp charger would be OK with that wiring. I tried using the Blue Seas circuit wizard using very conservative values, and it is suggesting 8 AWG for a 30A circuit which would require re-wiring. That estimate though is just for one wire.

My specific question is: does the charger output 30A on each output wire or split it (10A per wire)? If it splits the current I think l'm Ok with 10AWG for the 3 charger outputs. If not, then I will opt to remain with a 20 amp replacement, so as not to have to rewire. I read the Pronautic manual but couldn't find any references to the output behavior of the 3 DC posts with regard to amp splitting. Responses much appreciated in advance. Gary

The battery charger will most likely charge 1 battery bank at a time and cycles through all 3 banks.
How long is the cable run from the battery charger to the battery? Battery chargers require no more than 3% voltage drop across that distance.

10AWG can handle up to 20 amps at 3% or less voltage drop up to 15 feet round trip.
10AWG can handle up to 30 amps at 3% or less voltage drop up to 10 feet round trip.
8AWG can handle up to 30 amps at 3% or less voltage drop up to 10 feet round trip.

https://www.bluesea.com/resources/1437

 

[watson1987]

There might be some differences between the chart (https://www.bluesea.com/resources/1437) and the calculator (http://circuitwizard.bluesea.com), if you select "in engine room" it will increase the thickness of wire needed.

Assuming your wiring is appropriate, if you intend to use the 30amp charger, your existing 30amp fuses leaves no wiggle room, typically, you rate a fuse slightly higher to allow for short surges.

Installation
2. Fuse Selection - As illustrated in the diagram, each positive conductor from the charger to the
battery/battery bank must be fused. Choose a fuse that is 10 amps higher than the charger output
(e.g. 60 amps, choose a fuse of 70 amps)

From https://www.promariner.com/-/media/inri ... 0322141019

This PDF also lists cable gauge for various runs for the charger you have

 

[Submariner]

Those are additional great points.

Also consider this:
30 amps at 12.0 volts is 360 watts.
If the battery was at 10.5 volts, the battery charger could hit 34 amps.

I blew an 80 amp fuse on a 70amp battery charger from taking my firefly AGM battery bank down low (state of charge). I ended up replacing it with a 90 amp fuse.

 

[GaylesFaerie]

Thanks for the quick replies everyone. Here is more information:

1. I have 2 battery banks. One of the charger's outputs goes to the engine battery with a 30A inline fuse via the hot side of the Engine Service switch. The other two charger outputs go to the hot side of my Thruster and House service switches both with inline fuses of 30A.

2. The hot side of the Engine switch is connected to the engine battery via 1 AWG completing the path from the charger to the engine battery.

3. The hot sides of the Thruster and House switches use 1 AWG and are connected to a Positive bus bar. That bus bar has connections to each of the 3 House batteries (forming the second bank) completing their path from the charger.

4. Promariner support confirmed that output is split simultaneously across the 3 outputs depending on need. For example, if the House bank is full, all 30 amps will go over the single output to the engine assuming it needs charge. If the engine is full, the 30 will be split 15 and 15 over the Thruster and House outputs assuming the House bank needs charging. If the engine and house banks need charge then 30A will be split across all 3 outputs.

5. My R27 has the charger mounted on the starboard wall of the cockpit locker, the switches are mounted on the forward wall of the port generator locker, and the batteries are in the port quarter locker. The boat is 8.5' wide. Without being able to actually measure the cable lengths given their hidden routing I'm guessing the round trip is at least 20-25'.

Based on the above, these are my initial thoughts (open to any comments):

I don't need to worry about the two House bank output wires from the charger because that amperage will always be split between the 2 wires never receiving more than 15A each.

If I kept the 10AWG on the two House outputs should the 30A fuses be changed to something smaller?

The engine battery output, however, could under some circumstances receive a full 30A which would heat up that 10AWG. Could I take out the 30A inline fuse and replace it with something smaller (at the charger) to safeguard against that situation? Or is that too risky?

Could I just install a new 8AWG wire from the engine output to the engine switch?


Attached are diagrams of my switches and positive bus bar in case the narrative descriptions are too confusing.

Master Switches:
https://share.icloud.com/photos/0d4SRD7Uul00iDTiTc1rKBRAQ

Positive Bus Bar:
https://share.icloud.com/photos/0f1p3E57aytTWGMlQEoXwsY6Q
New updated Bus Bar image.

 

[Chimo]

A question from someone largely ignorant about such issues. If the full 30A could potentially be directed directly to the one starting battery, would that be good for the battery? I was always under the impression that slower charging was better as less heat was generated. In my thoughts I would rather wait a little longer to charge than go to the trouble of rewiring.

Just random thoughts.

 

[Red Raven]

Gayles Faerie,

Your analysis looks sound.

To use the 30A charger you need to re-wire the charger to Engine circuit with 8 gauge wire. The fuse on that circuit also needs to be changed to a 35A or 40A fuse to avoid blowing the fuse under worst case charging conditions.

Because your boat appears to have been re-wired to connect the thruster battery to the house bank it now has two 10 gauge charging wires to the house bank which will handle the 30A together. The fuses on these should remain at 30A. The fuse size is determined by the wire size to protect against fire.

Why do you want to change to a 30amp charger? When on shore power it usually means the boat will be staying at least overnight which will give it plenty of time for a full charge with the 20amp charger. I would personally just stay with the 20A charger.

I hope this helps.

Curt

 

[GaylesFaerie]

Thanks for you comments Curt. Yea, the more I think about this, staying with a 20A charger may be best for me (no re-wiring) and any future owner (scratching his head to figure out all this wiring).