Cristec battery isolator possible failure

SycloneDriver

SycloneDriver

.
Jul 23, 2009
917
Beneteau 31 Oceanis Grand Lake, Oklahoma
I've been chasing a voltage drop issue with my new alternator installation. I did find an issue at the house bank connection, it was tight and it looked clean but it was dropping 0.5 volts at only 5 amps. I cleaned it and now it's fine. But I still have about 0.7 volt drop between the alternator and the batteries. I figured it was probably the ground but it was not. My boat was factory equipped with a Cristec 100 amp battery isolator. Beneteau used the wrong lug on one of the cables and added 2 extra washers on the connection. Beneteau also used loctite instead of dielectric grease. I cleaned up all the connections and reassembled it but still have the same 0.7 volt drop. This is not a diode based unit it is supposed to have about 0.05 volt drop not 0.7. Is this the typical failure of MOSFET based isolator?
 
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dlochner

.
Jan 11, 2014
13,043
Sabre 362 113 Fair Haven, NY
Have you measured the voltage on both sides of the isolator?

Where were the washers installed? If washers are used the should only be places between the nut and the top connector and never between connections or between the lug and the device or battery. SS is a poor electrical conductor.
 
SycloneDriver

SycloneDriver

.
Jul 23, 2009
917
Beneteau 31 Oceanis Grand Lake, Oklahoma
dlochner said:
Have you measured the voltage on both sides of the isolator?

Where were the washers installed? If washers are used the should only be places between the nut and the top connector and never between connections or between the lug and the device or battery. SS is a poor electrical conductor.
Click to expand
The drop is between the alternator post and the house bank post. The washers are on the top and bottom of the alternator connection lug. I do not think it's a connection issue. The voltage drop is measured post to post.
 
SycloneDriver

SycloneDriver

.
Jul 23, 2009
917
Beneteau 31 Oceanis Grand Lake, Oklahoma
This was taken before I cleaned the connections.

It is not in an easy to reach location. Everything on this boat seems to be more difficult to reach than on my smaller Beneteau.
 
D

dlochner

.
Jan 11, 2014
13,043
Sabre 362 113 Fair Haven, NY
SycloneDriver said:
The washers are on the top and bottom of the alternator connection lug.
Click to expand
Remove the bottom washer. It may be part of the problem and it is dangerous. The additional resistance from the washer can cause the connection to over heat, which besides being a fire hazard increases the resistance in the connection. Second because the SS washer and the lug and bolt are different materials they will expand at different rates. This can cause the nut to become loose and subsequently the connection will become loose.

This article from MaineSail touches on the washer issue.

marinehowto.com

Battery Melt Down Narrowly Averted - Marine How To

Note The Melting of The Battery Case (originally published July 2012) The connections to your batteries matter. How you make them, how you torque them and how clean they are all matter. Not following best practices or marine wiring standards can impact your personal
marinehowto.com

Nigel Calder talks about washers and alternators in this video:

 
SycloneDriver

SycloneDriver

.
Jul 23, 2009
917
Beneteau 31 Oceanis Grand Lake, Oklahoma
dlochner said:
Remove the bottom washer. It may be part of the problem and it is dangerous. The additional resistance from the washer can cause the connection to over heat, which besides being a fire hazard increases the resistance in the connection. Second because the SS washer and the lug and bolt are different materials they will expand at different rates. This can cause the nut to become loose and subsequently the connection will become loose.

This article from MaineSail touches on the washer issue.
Click to expand
I understand that the washers are not ideal. The voltage drop is literally post to post, not lug to lug. It is possible that there is an internal connection issue. My question is really what is the failure mode of a MOSFET based isolator. I did not remove the isolator because it's a pain in the a$$ to reach, it would be different if I was young and fit.

I've probably read 90% of Maines articles. He is a very smart guy and we are lucky to have him.
 
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Davidasailor26

Davidasailor26

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May 17, 2004
5,715
Beneteau Oceanis 37 Havre de Grace
Sorry I don’t know the failure modes, but I have measured my isolator drop (same model) at 0.11V at 30A. So it’s at least possible for them to meet their specs.
 
SycloneDriver

SycloneDriver

.
Jul 23, 2009
917
Beneteau 31 Oceanis Grand Lake, Oklahoma
Davidasailor26 said:
Sorry I don’t know the failure modes, but I have measured my isolator drop (same model) at 0.11V at 30A. So it’s at least possible for them to meet their specs.
Click to expand
Thanks. That's the kind of information I'm looking for. Next time I get to the boat I'll remove it and take it apart.
 
SycloneDriver

SycloneDriver

.
Jul 23, 2009
917
Beneteau 31 Oceanis Grand Lake, Oklahoma
Today I removed my battery isolator and took a peek inside. Nothing looked out of the ordinary. I cleaned the posts again and reinstalled it. It still has a 0.7 voltage drop across it.
 

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jssailem

jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
23,341
CAL 35 Cruiser #21 moored EVERETT WA
Is this voltage drop new or is it the first time you observed it?

I do not use an isolator to direct the charge current. It is handled through an ACR. This reduces the voltage loss.
 
SycloneDriver

SycloneDriver

.
Jul 23, 2009
917
Beneteau 31 Oceanis Grand Lake, Oklahoma
I've always had low (13.4v) charging voltage from the alternator. I just assumed that it was due to the Hitachi internally regulated alternator. I recently upgraded to a Balmar alternator. Currently I am using the internal regulator. At the back of the alternator I have 14.1v just as I should but at the batteries I only have 13.3 to 13.4v. I traced the voltage drop down to the isolator.

I do not know when the issue started. I'm going to assume that the voltage drop has been there since I purchased the boat about 3 years ago and I just didn't realize that it.
 
jssailem

jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
23,341
CAL 35 Cruiser #21 moored EVERETT WA
There are many ways to put the system together. Lots of considerations, voltage drop being one of them.

When I bought my boat, all of the systems were aged. The process has been protracted. I broke it down into phases the basics Alternator, voltage regulator, charger, proper fusing and associated wiring being phase 1. I just completed phase 2 - installing a starter battery, ACR system, replaced 1/2/B switch with 3 switch system, galvanic isolator and new AC ELCI breaker system.

Now in the middle of Phase 3 new DC panel, new batteries and boat wiring with SG200 monitor.

It can be a huge project or you can do it in phases. The key is to first define the current structure, identify what types of systems you want, then build a plan to install the systems.

Sounds like you are still in the initial steps of identifying what you have. Certainly learning about the current system the strengths and weaknesses is the first phase.:)
 
SycloneDriver

SycloneDriver

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Jul 23, 2009
917
Beneteau 31 Oceanis Grand Lake, Oklahoma
I'm definitely finding weaknesses that I didn't expect. Like the use of loctite on many of the connections, this just doesn't seem like the correct use of thread locking compound. I'm going to blame the loctite for the bad connection on the ground switch. Speaking of ground switch, why did Beneteau install switches on the ground? My other Beneteau had one too.

The voltage drop across the isolator was a surprise too but I should have checked that before I replaced the alternator.
 
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