Re: [electricboats] Re Power for SV/Retreat Time Catamaran

Sure, if the voltages reported were the same a 20% higher current on the Sevcon would be odd.

Definitely check this because when you went to a steeper pitch the motor current went up for a given motor voltage.

Motor current could easily be 20% or even 50% or higher than the battery current---again, because the controller is effectively trading voltage for current thru switching.

-MT

 

From: electricboats@groups.io [mailto:electricboats@groups.io] On Behalf Of Dan Pfeiffer
Sent: Friday, June 2, 2023 2:50 PM
To: electricboats@groups.io
Subject: Re: [electricboats] Re Power for SV/Retreat Time Catamaran

 

Agreed but Sevcon was reading about 20% higher than Victron.  And I think Sevcon and Victron voltages did match but I will have to check that.  There are some calibration factors in the canbus translator.  I have not explored it in detail. 

Dan Pfeiffer

On 2023-06-02 4:20 pm, Myles Twete wrote:

Regarding the discrepancy in current readings between the Sevcon and Victron, it could be due to the Sevcon reporting motor current while the Victron reports battery current.  The controller, being a switching power converter effectively can deliver a very high average current at an average voltage (at the motor) of less than the pack.  Meanwhile, I imagine the Victron reports battery voltage and current.  The product of each I,V pair should come out close to the other (minus controller losses).

 

-MT

 

From: electricboats@groups.io [mailto:electricboats@groups.io] On Behalf Of Dan Pfeiffer
Sent: Friday, June 2, 2023 11:29 AM
To: electricboats@groups.io
Subject: Re: [electricboats] Re Power for SV/Retreat Time Catamaran

 

Have you got any performance data? 

My setup is very similar.  12500lb, 33ft (28.3 LWL) monohull.  I also have the Thunderstruck 12kW liquid cooled (ME1616).  I have  3:1 reduction that I fabricated myself and a three bladed 18" feathering prop that I can adjust the pitch on.  My performance has exceeded the predictions by 10-15% and I think that is largely due to being able to more closely match the prop to the motor and reduction gear.  

This season I increased the prop pitch by 1 setting.  The effective change in pitch is approximately from 13.5" to 15" so from 18x13.5 to 18x15.  I only have one set of data and it seems like I have increased the performance significanly with this change.  Like 30% less power for same speed.   It seems too big an improvement to be believed so I will need to collect more data and change the pitch back to repeat the data collection at the previous setting.   And at the lower pitch setting max throttle would peak at 250 amps or so.  Now I saw it spike up to 310amps which is above C rating (280 amps) so I need to check on that least I cause some damage.   But that was the value from the Sevcon through the bluetooth to my tablet and it does NOT agree with the Victron BMV712 which I trust for being correct for power draw on with it's shunt. 

So, interesting but more data to collect.  I built a new cooling system controller and I need to install that before proceeding to high power testing. 


Dan Pfeiffer

 

On 2023-06-02 8:34 am, kurtphone@gmail.com wrote:

 

I have a 34', 13500 lb keel/centerboard cat/ketch with a Thunderstruck 12kw watercooled kit. Prop is 17" x 13" fixed 2 blade. I am using the "large" Thunderstruck 2.5-1 gear reduction which is chain rather than belt. Initially the boat was over-propped and the current draw overwhelmed the C rating of the bank. I bought 10' of SS #50 roller chain, 3 different size motor sprockets and a chain breaker all for  $200. Changing the reduction ratio takes less than 1 hour and I do not have to haul the boat. Things are working much better now at 3.33-1. Interesting how good regen worked when it was over-propped. 

i am using a 3kw aircooled quiet generator on propane to reduce my range anxiety. I have it mounted in a cockpit locker with 2 x 3" 12 volt blowers evacuating the locker and a water jacketed extension exhausting out the transom. Temps in the locker are 110 degrees max. Generator can keep up with the load at 4 knots.