Lithiums - motor starting and the windlass

[catsketcher]

Hello all,

My 23 year old 38ft cat has a 1000 watt RC 8 maxwell anchor windlass. It works very well with our 2 house batteries powering it. The anchor windlass is only about 3 metres away from the house batteries. (The windlass is about 3.5 metres aft of the forebeam on the cat.)

The present house batteries are two T105 Trojans. Nice batteries and doing well. But I would like to make the bank bigger, so I am thinking of 200 AH of drop in Lithium. (Effective discharge AH is nearly doubled)

Our cat is powered by two outboards. The alternators on these things are anaemic at best and the voltage drops very quickly. So even though I usually have them on when pulling up the anchor, I am not sure they do much (max output is 13 amps) so maybe 20 amps when voltage is down when pulling up the anchor. Not much compared to the almost 100 Amps the 1000 watt windlass motor can pull.

So I am thinking of running the windlass off the lithium house batteries. The Lithiums I am thinking of have a max current of 200 Amps. If at 100 amps the windlass takes 2 minutes to retrieve the anchor, then we use 3.33 AH, which is not much at all. I would hope that with the lithiums, I would get much reduced voltage drop when winching and so the windlass motor would be better protected from too much current. As long as Lithiums can handle the load and there is nothing I am missing from the battery specs.

I would then isolate the lithiums from the two outboards and have a totally separate motor battery system, run from small mower lead /acid batteries (the motors are 25 and 9.9 hp each - yes they are different each side - long story). That way I don't get into any issues with lithiums getting charged improperly by cheap alternators and can put the starter batteries next to the motors. At the moment I have long leads running from the house batteries - I once had dedicated starter batteries and it was okay but went back to running the motors to the house batteries (I think to help the windlass and I can't work out if it worked) - but I have had some issues running long cables to the motors in a seamanlike fashion.

Is having the isolated systems a good idea - with small lead/acid for starting and alternator protection, and lithium for house and windlass, the lithium charged by 400 watt of solar? I will still carry our small lithium jump starter pack, which we have never used, for backup.

Is it worth bothering connecting the motors to the lithiums? I can easily put on extra solar to make 800 watts if needed. The cat has lots of space for more panels. I haven't run the motors to make electricity since we got the 400 watt panels going, that is back in 2013 and about 15 months of liveaboard cruising since, so we can safely say they are not required for house charging.

cheers

Phil

[Maine Sail]

Originally Posted by catsketcher

Hello all,

My 23 year old 38ft cat has a 1000 watt RC 8 maxwell anchor windlass. It works very well with our 2 house batteries powering it. The anchor windlass is only about 3 metres away from the house batteries. (The windlass is about 3.5 metres aft of the forebeam on the cat.)

The present house batteries are two T105 Trojans. Nice batteries and doing well. But I would like to make the bank bigger, so I am thinking of 200 AH of drop in Lithium. (Effective discharge AH is nearly doubled)

Our cat is powered by two outboards. The alternators on these things are anaemic at best and the voltage drops very quickly. So even though I usually have them on when pulling up the anchor, I am not sure they do much (max output is 13 amps) so maybe 20 amps when voltage is down when pulling up the anchor. Not much compared to the almost 100 Amps the 1000 watt windlass motor can pull.

So I am thinking of running the windlass off the lithium house batteries. The Lithiums I am thinking of have a max current of 200 Amps. If at 100 amps the windlass takes 2 minutes to retrieve the anchor, then we use 3.33 AH, which is not much at all. I would hope that with the lithiums, I would get much reduced voltage drop when winching and so the windlass motor would be better protected from too much current. As long as Lithiums can handle the load and there is nothing I am missing from the battery specs.

I would then isolate the lithiums from the two outboards and have a totally separate motor battery system, run from small mower lead /acid batteries (the motors are 25 and 9.9 hp each - yes they are different each side - long story). That way I don't get into any issues with lithiums getting charged improperly by cheap alternators and can put the starter batteries next to the motors. At the moment I have long leads running from the house batteries - I once had dedicated starter batteries and it was okay but went back to running the motors to the house batteries (I think to help the windlass and I can't work out if it worked) - but I have had some issues running long cables to the motors in a seamanlike fashion.

Is having the isolated systems a good idea - with small lead/acid for starting and alternator protection, and lithium for house and windlass, the lithium charged by 400 watt of solar? I will still carry our small lithium jump starter pack, which we have never used, for backup.

Is it worth bothering connecting the motors to the lithiums? I can easily put on extra solar to make 800 watts if needed. The cat has lots of space for more panels. I haven't run the motors to make electricity since we got the 400 watt panels going, that is back in 2013 and about 15 months of liveaboard cruising since, so we can safely say they are not required for house charging.

cheers

Phil

What is most important is how much in-rush you have. FETS can be damaged going above their safe rating.

This article will walk you through it...

https://marinehowto.com/drop-in-life...ated-consumer/







.

[smj]

We have a setup almost identical to yours. A Maxwell RC6 windlass, 2 drop in 100amp lithium’s charged by 640 watts of solar and twin 9.9 Yamahas that are started with a small single lawnmower/tractor battery.
We changed from 4 6volt golf cart batteries to this system about 5 months ago and have been very happy.
We put an 18 amp dc>dc charger between the starter battery and lithium’s to help charge the lithium’s if we have a day of motoring. The problem with the small capacity starter battery and the low output but not well regulated motor rectifiers is the voltage on the starter battery jumps above 15v in a matter of minutes. We have the dc>dc set to start charging when the starter battery reaches 14.2, and to stop charging at 12.2 so the starter battery can recoup. Only problem is it only takes about 10 seconds for the starter battery to drop down to 12.2, and about the same to build back up to 14.2, so the dc>dc is doing plenty of work. We also installed a battery selector switch per motor to shut of the charge coming from the motors to the starter battery.
We run our smaller windlass directly of the lithium’s with no problems. When we ran it off the 4 golf cart batteries the voltage would drop down into the mid to upper 11’s, even with the motors charging. Off the lithium’s the least we’ve seen the voltage at is 12.94, and that was running the windless with no charging coming from the motors.
I think this would be a perfect setup for us if we could find a 6-10 amp dc>dc that had a lithium friendly charging profile as the 18amp seems a little big for the job.

[catsketcher]

Thanks,

The Renogy 100AH batteries have a max current of 200A, with a 15 second excess up to 230A. I don't think the windlass would pull 200A for long, I don't make it work hard. I understand the Physics of start up currents and back emf and try to keep the windlass spinning as fast as possible to reduce current. We pull the anchor up in easy bursts, waiting for the engines and pull of the catenary to loosen the chain before switching on again. The 1000 watt inverter is used sparingly and not for high loads.

The Renogy DC to DC converter can handle lithiums. I wonder if it would be better to use a slightly larger starting battery, so that the voltage does not change so much under charge from our alternators. That being said, the Trojans at 200AH are very easy to observe being charged by the solar, and can increase voltage by almost 2 volts very quickly when the panels are switched on, so going bigger may not be useful at damping voltage fluctuations.

SMJ - the dropping of voltage at the starter battery implies that the DC converter is pulling lots more current from the battery than being supplied. So it seems as though the Yamahas are only putting out about 8 amps or so, hence the desire for a smaller charger I guess.

My mate with two Yammie 9.9s can switch his batteries off when motoring because the voltage gets too high (as it seems to do on your boat). I have one 25 hp which is regulated to 13 volts (Seems low) and one 9.9, so maybe I should disconnect the 9.9 when motoring for longer times and put the DC to DC off the 25 only. It was how the boat was setup for about 15 years and worked well. (when we had a single motor).

Thanks for the feedback

Phil

[smj]

The problem with the 18 amp DC to DC is its constantly working back and forth every 10 seconds which makes me think it won’t last long? At a smaller amp hour rating it would take longer to deplete the small starting battery therefore not working or switching as often? Maybe the key is to monitor the starting battery and when it reaches a good charge just disconnect the engines from the battery?
This is my only query in regards to our setup.
We have a 75 amp breaker on our windlass and in the 5 years we’ve used it only tripped the breaker once when the line got jammed. Your windlass is bigger but honestly don’t think you’ll have a problem.

[sailorboy1]

My windlass is powered from the start battery circuit, which is a SLA battery. My 400Ah LFP feeds into the circuit via a FET isolator. That means for the most part the LFP batteries bring up the anchor. I changed it for a while so that the LFP could not feed into the start circuit and that just made the windlass run slower so I changed it back.

Been this way 4 months of anchoring out and everything is good.