T&T: Battery monitor

[Randy Thompson]

Let me start by saying that I do not know much about this but I am trying to
learn enough to be safe as well as do things correctly as I see no sense in
doing anything else.

I am doing something similar and was unable to find the draw for the starter
for my John Deere 4045 (120HP 4.5 liter 4 cyl turbo). I contacted the folks
at John Deere and they indicated that it would draw significantly in excess
of 500 AMPs and indicate that I should use a 1000 AMP shunt.

The folks at John Deere mentioned a formula but sadly, I forgot what it was.

Looking around in the books I have collected and on the internet I find a
few things:

The Pacific Power Batteries web site has this snippet:
"3-cylinder diesel engine, 600-700 CCA; 4-cylinder diesel engine, 700-800
CCA; and 8-cylinder diesel engine, 800-1200 CCA".

According to "The Practical Mariner's Book of Knowledge", the rule of thumb
is 2 CCA's per cubic inch of displacement.

My 4.5 litres is approx 274.6 cubic inch engine. Using the above rule of
thumb, the draw should be around 550 CCA's. 10% above the 500A rating or
more than this if I use the rule of thumb by Pacific Coast Batteries.

>From the Blue Sea Systems web page:
(http://bluesea.com/productline/overview/202) Blue Sea shows their shunts
rated for intermittent duty of 100% for 5 min and 300% for 3 seconds.
Continuous duty is rated at 66%.

Xantrex does not appear to have much technical detail on their web site but
also indicate that Diesels can draw too much current for their 500AMP dual
shunt. They suggest either bypassing the starter motor if possible (see
http://www.xantrex.com/web/id/73/DocServe.aspx) or using a heavy duty shunt
for the starter load.

At current, my plan is to do as recommended by John Deere and use the heavy
duty shunt for the starting circuit. This will mean tying the grounds
together from the 500AMP and 1000AMP shunts. Not really to big a deal.

Hope some of this is useful,

Randy Thompson
Soul Tender
KK39007



On 3/29/09 7:47 AM, "Truelove39 at aol.com" <Truelove39 at aol.com> wrote:

> Hi Steve,
>  
> I believe you'll be OK with the standard 500A shunt. I have a Link 2000
> which I'll soon install and it has a 500A shunt standard as well - I won't be
> changing it even tho' our starter draws almost that.
>  
> A shunt should not be sized to carry maximum expected load. Standard practice
> is to size it so that it carries a continuous load  of no more than 2/3 of
> its rating. Exceeding this will likely  change the accuracy of the shunt and
> may 
> eventually destroy it. Short-term  loads such as starters which draw or even
> slightly exceed maximum rating  are allowable as long as the shunt temperature
> doesn't exceed 80C. It's  unlikely that typical trawlers have starters which
> exceed 500A although they may  be near to that. Most windlasses for boats our
> size seldom draw more than  150A. I don't know anything about thrusters except
> from time to time I  wish we had one! It would be best to locate a shunt
> outside the engine room and  outside the battery locker too if you have
> lead/acid 
> batteries, as the  fuseholder terminals will likely corrode otherwise.
>  
> Regards,
>  
> John
> "Seahorse"
> 
> 
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