Bow Thruster with terminal fuse blown

N

Nheels

Petty Officer 2nd Class
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Mar 8, 2021
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126
Hi all, recently had a 2.2kw Lewmar 140TT bow thruster installed. Yesterday when going to use it, noticed that it wasn't working due to low voltage. After some investigation, I found that there was a blown 80amp terminal fuse on the starter battery. Now I have made a rough diagram and have attached it as it will serve better then trying to explain!

I wondering if anyone sees errors in this set up or have any ideas as to what would have blown the fuse? The thruster was professionally installed, so I assumed that the 80amp fuse was what was needed, but maybe they should have put in higher load fuses? The thruster is, afterall, protected by the 200amp circuit breaker. I tried looking up what fuse should be used, but couldn't find much unfortunately.

6 guage wires running from the stern to the bow and thicker ones running from the thruster battery to the actual thruster a few feet away.

With the fuse blown, there was not juice going through to the ACR to the bow thruster battery. That battery read 9.5v before I trickle charger it over night. It's holding a charge now.

I don't know when the fuse blew.. just when the battery didn't have enough in it to work.

Any help would be appreciated! Thanks.
 

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Silvertip

Silvertip

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Mathematics blew the 80 amp fuse (P=E x I (power = voltage x current). 2200 watts (2.2kw) divided by 24 volts = 91+ amps (possibly more at initial starting load). The 200 amp breaker on one battery didn't blow because it was big enough (perhaps too big for the wire size. Doing that causes the wire to burn before the breaker opens. The 80 amp fuse obviously is not big enough. Next, 6 gauge wire is good for 55 amps and 100 amps requires 3 gauge. Total length of the circuit can impact wire sizing as well as long runs results in losses that are compensated for by increasing the wire size. You perhaps should look for different professional when it comes to electrical installations.
 
N

Nheels

Petty Officer 2nd Class
Joined
Mar 8, 2021
Messages
126
Silvertip said:
Mathematics blew the 80 amp fuse (P=E x I (power = voltage x current). 2200 watts (2.2kw) divided by 24 volts = 91+ amps (possibly more at initial starting load). The 200 amp breaker on one battery didn't blow because it was big enough (perhaps too big for the wire size. Doing that causes the wire to burn before the breaker opens. The 80 amp fuse obviously is not big enough. Next, 6 gauge wire is good for 55 amps and 100 amps requires 3 gauge. Total length of the circuit can impact wire sizing as well as long runs results in losses that are compensated for by increasing the wire size. You perhaps should look for different professional when it comes to electrical installations.
Click to expand...
The cable running from the starting battery is for charging is what I gather. The bow thruster isn't running from that battery as it has its own, so that 6 guage should be enough.

It was almost like it was pulling the bow thruster load from that starter battery, but I can't see how that would have happened as there is a ACR-SI there to prevent that. From what I gather, the acr isolates the bow thruster from the other battery for discharge purposes. At least that's what the bluesea website says.

Should mention that 5hisnis a 12v system.
 
Last edited:
dingbat

dingbat

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Nov 20, 2001
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16,313
Nheels said:
It was almost like it was pulling the bow thruster load from that starter battery, but I can't see how that would have happened as there is a ACR-SI there to prevent that. From what I gather, the acr isolates the bow thruster from the other battery for discharge purposes.
Click to expand...
Where is the wiring for the start isolation feature?

Without it, your drawing from both batteries this the blown fuse
 
dingbat

dingbat

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Messages
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Nheels said:
Back charge as in the bow thruster battery charging the starter battery?
Click to expand...
Yes…..ACR (automatic charge relay) is a voltage activated relay. When the ACR active, current is free to flow in either direction.

If the bow thruster battery has the higher potential of the two, it will charge the starting battery and vice versa.

In effect, you’ve in effect tied the two batteries together to make one big battery. As wired, the bow thruster pulls from both batteries.

To isolate the batteries during from one another during ise you need to wire the SI functionality
 
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