Wire directly to battery negative? That doesn't work for me

[jordanbigel]

Some electronics devices manufacturers specify in their instructions to wire directly to battery negative. I'm thinking of bilge pumps for example, but also I read this recently in my reefer compressor installation instructions.

So, purely as an academic question (because long ago I decided to wire the compressor negative to the negative bus bar regardless of manufacturers suggestion, which goes through the shunt which measures battery SOC%, otherwise my SOC% would be wildly out of sync with reality) - I'm wondering about this issue in a more general sense.

For example, for a bilge pump, that might not sound important, but we often run our bilge pumps on manual in various circumstances (e.g. washing out the bilge). So I want the bilge pump to also be wired through the shunt to keep the SOC% as accurate as possible.

Is there any valid reason to wire anything directly to battery negative, bypassing your SOC% tracking shunt?

NB: All this assumes that I am aware of and have successfully ensured that all connections are clean and of high quality, wire sizes adequate or even oversized, and that voltage at the device itself has not suffered any losses, etc., etc.

[Chotu]

I think a lot of times they assume a more simple electrical system when they are saying that.

there is really no difference between a negative bus bar that is connected to the battery through a shunt and connecting directly to the battery.

[capt jgw]

I think they mean don't put a fuse or switch in the negative wire. You can consider the output side of the shunt to be B-.

[barnakiel]

You avoid going thru the shunt only when your shunt is sissy.


I have worked on a few boats and I can assure you the real big things have NOTHING wired to the battery directly. The batteries go to bars, and there can be things wired directly to the bars, but NOT to the batteries.


b.

[jordanbigel]

Originally Posted by capt jgw

I think they mean don't put a fuse or switch in the negative wire. You can consider the output side of the shunt to be B-.

All of the responses are what I was expecting.

However, to address the above "...I think they mean don't put a fuse or switch..."

Here is the relevant part of the installation manual for a reefer compressor - to be fair, this is stated as a "recommendation" but it is worded quite strongly, and there is no mistaking this statement as implying or intending to convey a warning about fuses or switches (which would be highly unusual in a neg ground wire regardless).


PS: I am thrilled with my reefer system, which I installed about 2 years ago and which has been working flawlessly since then even in the equatorial heat of the central pacific.

[FlyingScot]

Its CYA for them as a bad negative causes issues for them. No harm having a large negative bus bar close to the battery. Skipping your shunt or putting too many connections on a single post creates issues for you.

Call Rich or send him a WhatsApp and ask him about your situation.