Making a cheap BMS ABYC compliant

[newhaul]

Originally Posted by s/v Jedi

Why does it have to be able to crank the engine? How does that decide if it will absorb a transient surge?

These miniature AGM batteries may just turn out to be good protection devices. I think they will do better than a big capacitor.

Thinking of alternator size and relevance to size of engine 75 amp is biggest I can power on my 10-2 now you can power a 250 amp bus alternator on a big cat engine .

[PaulCrawhorn]

A lead battery is fine for cranking your engine. Very cheap to replace long before starting to worry about its reliability.

And it is the best simplest solution for the "Alt damage from LFP disconnect" problem.

I really do not understand why anyone would consider a more complex thus fragile and less certain solution to that problem.

Sure if your design does not allow a lead Starter (huh? why not?) you could do all the testing required to see how small a battery would still work, but there are so many variables involved I think better to avoid that particular project.

But if you do it, please let us know the result...

[goboatingnow]

Originally Posted by PaulCrawhorn

A lead battery is fine for cranking your engine. Very cheap to replace long before starting to worry about its reliability.

And it is the best simplest solution for the "Alt damage from LFP disconnect" problem.

I really do not understand why anyone would consider a more complex thus fragile and less certain solution to that problem.

Sure if your design does not allow a lead Starter (huh? why not?) you could do all the testing required to see how small a battery would still work, but there are so many variables involved I think better to avoid that particular project.

But if you do it, please let us know the result...

More complex ? How

[newhaul]

Originally Posted by PaulCrawhorn

A lead battery is fine for cranking your engine. Very cheap to replace long before starting to worry about its reliability.

And it is the best simplest solution for the "Alt damage from LFP disconnect" problem.

I really do not understand why anyone would consider a more complex thus fragile and less certain solution to that problem.

Sure if your design does not allow a lead Starter (huh? why not?) you could do all the testing required to see how small a battery would still work, but there are so many variables involved I think better to avoid that particular project.

But if you do it, please let us know the result...

Not necessarily much more complex but definitely more expensive .
Consider a 1200 watt generator will run a 75 amp charger and is cheaper than the adjustable external alternator regulators. Not to mention much more efficiently than the main engines. Just run a lead start bank and a 50 amp dc dc to your LifePo4 bank no problems exist. Stop trying to complicate a simple thing.

[goboatingnow]

Either way upgrading your alternator to a proper external temp sensing with remote control is a good idea anyway. The stock alternator regulators are not optimised to charge batteries anyway. Having remote on off is useful anyway.

Nothing complex in it, irrespective

It’s horses for courses and avoids the cost of needing big dc dc converters.

Both approaches work , one has different advantages over the other.

[PaulCrawhorn]

Using a lead batt to buffer is completely independent of the choice between DCDC and upgrading to an external VR.

Originally Posted by goboatingnow

Either way upgrading your alternator to a proper external temp sensing with remote control is a good idea anyway.
...
Both approaches work , one has different advantages over the other.

[newhaul]

Originally Posted by goboatingnow

Either way upgrading your alternator to a proper external temp sensing with remote control is a good idea anyway. The stock alternator regulators are not optimised to charge batteries anyway. Having remote on off is useful anyway.

Nothing complex in it, irrespective

It’s horses for courses and avoids the cost of needing big dc dc converters.

Both approaches work , one has different advantages over the other.

Let's see a balmar Mc 618 is $600. A 40 amp dc dc renogy for lfp is $160 and stackable
So for a 100 amp alternator 2 dc dc is $ 320 for 80 amps the other is 600 for 80 amp output.
Lead start then dc dc Eliminates the need for the protecting from bms HVC spike .
Most of us already have a lead based start bank .
Why complicate a simple setup .

Now my question is what are you being irrespective of?

[s/v Jedi]

Originally Posted by newhaul

Let's see a balmar Mc 618 is $600. A 40 amp dc dc renogy for lfp is $160 and stackable
So for a 100 amp alternator 2 dc dc is $ 320 for 80 amps the other is 600 for 80 amp output.
Lead start then dc dc Eliminates the need for the protecting from bms HVC spike .
Most of us already have a lead based start bank .
Why complicate a simple setup .

Now my question is what are you being irrespective of?

This is why that setup is my primary reference diagram. However, some boats have little or no solar and depend on a large alternator for house battery charging.

So while 60A or 80A isn’t an issue, 140A or 225A is. Before we switched to large solar arrays, we had 3 alternators on the engine: the standard Hitachi for the start battery, plus two (!!) massive Lestec Brute225A alternators for 450A charging. You can’t do that with dc-dc chargers, but I could do it with a aingle smart regulator

[newhaul]

Originally Posted by s/v Jedi

This is why that setup is my primary reference diagram. However, some boats have little or no solar and depend on a large alternator for house battery charging.

So while 60A or 80A isn’t an issue, 140A or 225A is. Before we switched to large solar arrays, we had 3 alternators on the engine: the standard Hitachi for the start battery, plus two (!!) massive Lestec Brute225A alternators for 450A charging. You can’t do that with dc-dc chargers, but I could do it with a aingle smart regulator

Agreed but wouldn't eliminating the HVC surge potential remove the requirement for an alternator cutout which is not present on a " cheaper Mosfet controlled " bms such as a Daly. Solve the issue at hand.
Also I rather doubt Daly makes a bms big enough for a bank the size that you have.

[goboatingnow]

Originally Posted by newhaul

Let's see a balmar Mc 618 is $600. A 40 amp dc dc renogy for lfp is $160 and stackable
So for a 100 amp alternator 2 dc dc is $ 320 for 80 amps the other is 600 for 80 amp output.
Lead start then dc dc Eliminates the need for the protecting from bms HVC spike .
Most of us already have a lead based start bank .
Why complicate a simple setup .

Now my question is what are you being irrespective of?

STERLING
DIGITAL High-Performance Regulator / waterproof. 174 euros complete with temp sensor.

So again not sure what point

[CarlF]

Originally Posted by PaulCrawhorn

A lead battery is fine for cranking your engine. Very cheap to replace long before starting to worry about its reliability.

I've been doing just that for the last year. Didn't use an AGM start battery needing charge profiles. Plain-old "sealed" lead car batteries aren't picky about charge voltage because they were designed when cars had generators not alternators with no regulators at all. And modern diesels start so easily that the battery is never deeply discharge so there's never a lot of charging.

My start battery spends 95% of it's time at full charge connected to a lithium bank that's between 13.1v-13.4v - as far as the start battery knows, it's connected to a float charger.

I don't see why this start battery won't last a very long time.

[newhaul]

Originally Posted by goboatingnow

STERLING
DIGITAL High-Performance Regulator / waterproof. 174 euros complete with temp sensor.

So again not sure what point

180 plus tax usd
Again cost dc dc is still cheaper and doesn't require any complexity to protect alternator from HVC spike as the lead start bank absorbs the spike..
This is the thread about making a cheap BMS ABYC Compliant. With lead primary dc to dc lifepo4 no warning or early shutoff is required.
Considerably less complex. As you require a dc dc with your setup as well just a smaller one .
Start running systems like the rest of us and you will realise a few things .

[goboatingnow]

Originally Posted by newhaul

180 plus tax usd

Again cost dc dc is still cheaper and doesn't require any complexity to protect alternator from HVC spike as the lead start bank absorbs the spike..

This is the thread about making a cheap BMS ABYC Compliant. With lead primary dc to dc lifepo4 no warning or early shutoff is required.

Considerably less complex. As you require a dc dc with your setup as well just a smaller one .

Start running systems like the rest of us and you will realise a few things .

The cost difference is actually very marginal as a very cheap 10A starter trickle dc dc can be found for $50

Tbd point being each alternative approach has similar costs and different benefits

Firstly the direct alternator approach maximises the alternator LFP charging ability. Secondly the starter battery suffers no cycling effects when LFP charging and thirdly better alternator regulators are a good idea anyway.

Dc dc from LFP to starter has much to recommend itself as every charge source on the boat charging the LFp can also via the dc dc charge the lead acid offering considerable piece of mind.

Where an alternator charge strategy is prominent , an alternator direct strategy has much to recommend itself.

[newhaul]

Originally Posted by goboatingnow

The cost difference is actually very marginal as a very cheap 10A starter trickle dc dc can be found for $50

Tbd point being each alternative approach has similar costs and different benefits

Firstly the direct alternator approach maximises the alternator LFP charging ability. Secondly the starter battery suffers no cycling effects when LFP charging and thirdly better alternator regulators are a good idea anyway.

Dc dc from LFP to starter has much to recommend itself as every charge source on the boat charging the LFp can also via the dc dc charge the lead acid offering considerable piece of mind.

Where an alternator charge strategy is prominent , an alternator direct strategy has much to recommend itself.

Until you kill it from an unexpected HVC event then no alternator.
Unless you want to add another level of complexity unnecessarily.

[goboatingnow]

Originally Posted by newhaul

Until you kill it from an unexpected HVC event then no alternator.
Unless you want to add another level of complexity unnecessarily.

No evident HVC will kill alternators it’s all supposition

And as Nick others and I have pointed out protecting the Alternator very simple , and can easily be done by a number of means

No alternator is no biggie anyway.

As I contended , both methods have advantages and drawbacks. Both have their adherents but ultimately it comes down to personal proclivities and strategies. Fitting a regulator is no complex.

Even the basic idea of a field disconnect is very simply added.