Parasitic battery drainage in 2008 Tomcat

M

marcagrin

New member
My recently purchased 2008 Tomcat has a mysterious (to me) parasitic battery drainage that I cannot track down. I have 3 new Interstate deep cycle class SRM-27 batteries installed by Marc Grove-one of which is the house battery that is continually losing voltage. The alternator on the charging Honda 135 hp motor appears to work fine when needed. The 120v shore power via a Guest 5/5/10 20 amp 3 line 3 stage charger appears to top all 3 batteries off a about 12.7 volts (once charged and disconnected). Then, however the house battery gradually discharges to 12.4 volts within 48 hours of no use and -all items and all switches off.
My multimeter indicates 44 milliamps flowing from the positive house battery pole to the disconnected positive connecting wire with all electronics and switches off.. A test of resistance from the disconnected positive connector wire to the negative/ground battery pole indicates resistance too high to measure. Where are the amps draining to?
I do notice that the backlighting to the Blue Sea 120 AC distributer/breaker panel is always on. (I believe this is the normal operation mode-but am not certain). Could these 6 LEDs be draining that many amps?
I enjoy anchoring out in the boonies for several days at a time, so uncontrollable voltage loss is an issue.
Marc G
 
When you tested resistance, did you have the positive lead of the meter on the positive wire? LEDs are diodes, and would have extremely high resistance one way, much less the other.

I bet it is the LEDs. Wonder why they are not off when the console, etc., is shut down.
 
I would suspect the LED's. Do you have the main battery switch shut off for each battery? If not, you should. Do you have an VSR? Either a bilge pump sensor, which comes on every few minutes, or a drain by any of the electronics may be enough to pull the batteries down. Be sure that the "start battery" is fully isolated.

My Tom Cat had two start batteries, and one house. I increased that to 3 house, plus and inverter freezer bank.
 
Any chance there is a propane leak detector on the boat? On RVs, they are often connected on the hot side of the battery disconnect. Stereo components could be another.

I suspect Dr. Bob is correct, but I thought I would toss out other possibilities.
 
I would think a relatively easy test would be to remove ALL wires from the positive terminals on the house batteries. You should see no leakage while it's like that. Then add one wire at a time until you find the culprit.

I had a problem like yours once. The problem was that I was making assumptions about what was switched and fused where. Removing the actual wires is fool proof.
 
Going from 12.7 to 12.4V represents about 20-30% loss. 44mA *48hours = 2.1Amp-hours. The SRM-27 is I believe rated at about 65AH. 20-30% loss of 65AH would be around 13AH. So something doesn't add up to me. Either the battery is no longer anywhere near its rate amp-hour capacity OR the parasitic drain must be about 7x the 44mA you are reporting.
 
It could also be that the drain is not constant--such as the sensing type of bilge pump auto switch, which comes on ever several minutes. The 44 ma was when that sensor was not running. (If he has those (2) type of bilge pump sensors.
 
Another possibility is if you have a Blue Sea ACR (automatic charging relay). These, if wired the default way, have a load at all times (even when the battery switch is off). This caught me when I first re-wired the boat. I called Blue Sea, and they said yes, this always pulls a small load. Their first suggestion was to wire an additional small switch in the negative wire to the negative bus. This was somewhat unappealing to me as it is one more thing to forget (and besides, "automatic" is in the name!). I mentioned this, and they suggested an alternative, which has worked fine and has no parasitic load, and no extra switch to wire or remember. In my case this was to wire the two positive legs of the ACR to the two load sides of the switch (i.e. the sides that are not active when the switch is off). I have a Dual Circuit switch; other arrangements might be different.

I also got caught out by the fact that the Victron battery monitor draws a small amount (and is typically not wired to go off with the switch). However this is a very very small draw, and only noticeable over a very long time period. Given that, and that I want it on most of the time (even when switch is off), I simply pull the fuse on it for longer term storage (months).
 
Many thanks for the prompt and informative responses. (This is my 1st post as a newbie.) My concern is similar to Roger's-how do I get a 25% voltage drain from a 2.1 mA leak? I wonder if this 3 month old battery is starting to fail.
I have already replaced one failed automatic bilge pump with a manual connected to a float switch. The 2nd pump is a Rule automatic.There are no relay switches, propane sensors, stereos, etc.
Does anyone know if it is normal for a Blue Sea distribution panel to have constant back lighting even with the AC shore power disconnected. (The back lighting is not noticeable in daylight.) I am trying to contact Blue Sea to determine if this is atypical and indicates a wiring fault.
I will try reversing my leads in determining resistance and observe any differences.
 
Marc, does that boat have a CO detector ? If so they are normally direct wired to the house for safety . If you can find the source of power to the Blue Seas A/C panel ,it could be moved to the switched side of the battery switch so its not on all the time even with battery switch off . If you still have an electronic auto bilgepump in the system , you might consider changing to a float operated type as well .
Marc
 
Marc,
I disconnected that little CO detector hidden under the steering wheel. Also have emailed Blue Sea to see if I can disconnect the backlight without affecting the other distributer panel functions. Love the Tomcat, but I am a bit electrically challenged!
Happy 4th!
Marc
 
I just helped a friend to install a Blue Sea AC panel (8467, AC Main with two sources and four circuit positions). There is a pair of DC wires that gets hooked up and controls the backlighting function. We put in a switch (which I think was mentioned in the instructions) which controls the "white" backlighting. Then there are the colored LED's at each position - as I remember it they are always on when that particular circuit is energized, which makes sense (but this is separate from the backlighting/switch; the backlighting lights up the labels, etc.).

I just double-checked the instructions for that panel. Here is what they say (they do mention using a switched positive wire). Is your (white) backlighting not switched and therefore on all the time?

5. Installation of Backlight System
The backlight board is a DC device. When installing it in an AC panel both wire leads must be connected to an appropriate DC source and ground.
Connect the yellow negative wire to a DC ground. Connect the red positive wire to any DC positive supply, usually a switch that controls the vessel’s other nighttime illumination.

Since they likely won't be open for a few days, you can find instructions for each of their products here at their web page if you like. Just drill down through "products," etc. to the page for the specific panel you have.

www.bluesea.com

PS: As it turns out, my friend pretty much just leaves the backlighting switched off on the AC panel. I guess that just depends on how one uses the panel, where it is located, etc. But with the switch it can be like "you don't have it" most of the time, but then you can still use it when you want to.
 
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