Thanks in advance for the input.

I may have this wrong ... but I think the original engine alternator is still on, depicted just behind the white Alpha alternator, driven by the belt.

For other non-relevant reasons, I added a DC-DC charger for the engine start battery: Mastervolt Magic, the same as used to maintain the bow & stern thruster batteries.  Compact & very inexpensive by boat standards.

I guess I'm curious as to what problem you are trying to solve.       Dedicating the engine alternator might top off the house bank faster, but is that really a problem?   

I would think with solar or an upgraded alternator the existing setup could speed up enough to meet your expectations.

Hi Wayne,

I have a Victron DC-DC 20amp charger. Initially I had the 30 amp. 20 amp is way more than enough. Keep in mind that it will run your house bank down unless you have a way of topping it up (solar etc). Yes, it will mostly be in float mode, but it is always on - a consideration for when you are away from the boat for awhile. This setup works even better if your house bank is lithium - they accept as much power as you can throw at them, and are usually at a slightly higher voltage than the start battery. I'm four years into this setup and so far it's perfect,

regards,

Tim

The issue I am looking to fix is that - a guru electrician in Sint Maarten noticed our generator was starting off our lithium house bank and he suggested that was not a good idea so I changed the generator to start off the engine start AGM. There are cables to jump (the generator or engine) from the house bank if necessary. For some reason the alternator on the generator does not charge the start battery. Originally the alternator was shot and I replaced it but the new one doesn't charge either. This is generally OK but over a period of no use of the engine and starting the generator the start battery starts to get low. If I run the engine or motor sail for a while all is good but if we spend too much time at anchor without running the engine but using the generator the start battery will gradually go down. I have been occasionally charging the start battery with a 10 amp Victron charger. But I thought if I had a DC/DC charger in place it would be constantly topped off. We recently added some portable solar panels (2 x 220w) to our system which now gives us just under 1500w. This seems to mainly meet our needs unless we have some cloudy days in a row. 

I have 6x lead batteries , thrusters generator and main engine , and two large lithium batteries from mastervolt, the last one doing 90% of the job. even for starting the engine , as I discovered this summer...

I have solar panels too, and two mppts.

as Leon pointed out various times , and I completely agree , there is no perfect design.

however, ALL the issues I had in the last 5 years are ALL related to lead batteries. I had to replace all of them at least once.

despite the lead technology being culturally accepted without critical analysis because it is there since a large number of years , it has two fundamental problems:

1) the intrinsic fragility of the chemistry

2) the absence of onboard BMS that can handle device -specific individual issues: unit  temperature, charging /discharging currents control, float, cell normalization.

can we invent outside solutions and devices  to take care of these two problems ?yes , like we have palliatives for terminal diseases...they help , but they don't fix the fundamental issue.

so my strategy is : I don't invest into fundamental modifications of my system , but over time I am going to replace all 6x lead based batteries with lithium (or sodium) batteries...

times change. we have moved from the art of starting a cold engine , to fuel-less cars that don't care if the engine is cold or warm ...sometimes  you can't fix the past issues without a step change.

Wayne,    

it sounds like something else is going on.   On my boat the gen set will throw (say) 110 amps into the batteries (all of them) thru my mastervolt charger.   If I turn off the charger, the gen set alternator alone will throw 45-70amps into the batteries (all of them,  start, thrusters, house, etc).   Not sure why your gen set is not charging the start battery.

Why not simply add another small battery for generator start?    Why mess with the engine alternator charging setup?     

FWIW - 

https://www.youtube.com/watch?v=VZSr6o5fLHE&list=PLsT7_jPsZM5ogT6or244F49-Gy7pYFV7V&index=11" rel="nofollow - https://www.youtube.com/watch?v=VZSr6o5fLHE&list=PLsT7_jPsZM5ogT6or244F49-Gy7pYFV7V&index=11

Maybe you could just go back to the original setup of house bank starting the generator. Conventional wisdom is that deep cycle batteries, like most lithiums, aren’t suitable for start batteries because they don’t deliver the high cold-cranking amps that start batteries do. I’m not sure how big of a generator you have but they typically don’t require as much starting amps as a diesel propulsion engine. Depending on how much discharge current is available from your house bank lithiums, you might be fine. If it was working ok before, …

My 458 came from the factory set up with generator starting from the house bank but all the batteries are lead acid. It works fine even though the house bank batteries are deep cycle lead acids and not start batteries. If I ever make the jump to lithiums, I will probably keep it that way as the discharge capacity of the newer batteries and BMS’s seem to be more than enough to crank my Fischer-Panda 4k which recommends only a 28 amp-hour start battery.

Hi Wayne, if you already have lithium and lots of solar then DC-DC is perfect. I worked with Lead Acid for 10 years and while I'm no expert I do have good hard won knowledge. Lead Acid is fine (for the price) *IF* you keep it charged up. Don't let it get below 70-80% full and you will get good life out of good quality batteries. My previous set of AGM's lasted 11 years. My current ones are 5-6 years old. Let your lithium do the cycling up and down (in charge) and your lead acid do the short sharp heavy loads then recharge them. And keep in mind that lead acid is pretty foolproof - no fancy electronics involved - they make a great emergency backup in case of BMS failures etc.

The Bank Manager referred to below also seems an excellent product - if I was starting out again I would use it,

Tim

Rick, the electrician in Sint Maarten, Adam, fixed a couple of issues introduced when the Victron dealer in Malta oversaw the fitting of our lithium house bank and the additional 3000w/120amp charger in 2019. We had problems with the original charger/inverter and Adam showed me the Malta install had used smaller size cable to connect the new inverter which was also longer than the original cable for the first unit. This all made sense to me.  Whilst doing this work Adam noticed our generator was starting off the house bank (originally AGM but now lithium). His suggestion was to change this to either the engine start battery or add a separate generator start battery. Because Adam was the guru and we had worked with him for a few seasons whilst in the Caribbean I made the change. The easiest change was to start from the engine start battery. This suited me because generally I'm the "don't add extra complexity, cost or tech to a simple situation" type of guy.   

I thought adding a DC/DC charger to charge the engine start battery would be an easy fix to the problem of the new alternator on the generator not charging. We are now in Fiji and will not return to Aust until Oct 2026 I think the best solution would be to put up with the issue for that period and find a good electrician in Aust to sort out the charging. From what I have seen of the standard of technicians since being in Fiji I don't think I will get it fixed here. Particularly in the more remote areas we will be in.   

Currently when running our inverter/chargers on the generator we get about 200amps into the batteries, when running the Volvo about 100amp, solar (1465w) puts in upto 80amps and when sailing the Watt & Sea puts in about 20amps. When we fitted the original solar (1025w) I worked out we used about 250ah a day. But since then (2017) we have added an additional freezer, Starlink, extra appliances ( bread maker, air fryer etc etc) added the water heater and washing machine to the inverter circuit I think we can now use up to 450ah a day. So we increased our solar with two portable panels so we now have 1465w which on normal days works fine. But on the bad solar days we still need to run the generator. If we are running the watermaker (now 240V) we also need to run the generator. If we are filling scuba tanks we need to run the generator. So I will need to get the generator alternator charging sorted long term I can deal with in for now. 

Great to hear the thruster parts were of use. Your low tech mod to the combiner looks like my type of option. Our house bank of lithiums get to 100% charged normally 5 out of 7 days from our solar so this option would probably work well for me. What brand of combiner did you modify and how hard is it to modify? 

Our tunnel bow thruster is working a treat and no issues with it since fitting it in early 2023.