Making a cheap BMS ABYC compliant

[s/v Jedi]

Originally Posted by britinusa

Thanks.
I was wondering. If the B2B charger was at least in Float mode, then would there even be a transient surge? It didn't occur to me that it might ( or not ) absorb the surge. I'm not particularly educated about 'transient surges'

It doesn’t matter, the surge is a flyback voltage, caused not just by interrupting a current but also a sudden decrease.

You can learn about the principles, for example a wikipedia article about flyback voltage or flyback diodes will present the science behind it.

The problem isn’t that it happens, but the severity. If you disconnect a relay you also get it, but absorb it with a simple diode, but for an alternator going full out, you really need a connected battery to absorb it.

There are safeties that “may” prevent damage. Think of those like a fire extinguisher that may save the day but then again it may not. I started this thread to help people take care of this with the cheapest BMS on the market, but it won’t work for even cheaper setups.

[newhaul]

Originally Posted by britinusa

Here's the list of components of My System.

Victron Multiplus 12/3000/120/50
Victron Cerbo GX
Victron GX Touch 50
Victron Smart Shunt 500
Victron GX 4G LTE + T-Mobile Sim Card
Victron Mk3 - USB
Victron GPS Antenna
Victron Smart Battery Sense
Victron 100/20 Smart MPPT Solar Charger Controller with < 300w of solar panels.

Victron Orion DC/DC Charger 12|12-18

Starter Battery-12v Duracell AGM
House Battery 12V (2S2P Trojan T105 6V)
Balmar 100A ( Rod Collin's ) Alternator
Balmar MC 618 External Regulator with both Battery & Alternator Temperature Sensors


Plan is to change out the House Battery to LiFePo4 in the next few months. Hence why I'm asking about the protection of the Alternator

FYI, I'm also going to replace the solar panels and add a 2nd MPPT controller in the spring. That will probably be about 500w. 1 x 170w and 2 x 180w

Thanks.

Paul

Ok sounds like a good system was just wondering as for my setup solar is primary and alternator is a 75 amp internally regulated will be running a 50 amp dc dc charger from lead to 250ah lifepo4. For ontext I have not needed shore or alternator in 4 years but never know when it may be needed. But I'm not trying to be a slave to my battery bank . Have the battery a bms and a smart shunt and battery monitor . Also my mppt has Bluetooth so sends data to my phone if I request it to . Otherwise I just let my mppt do its job as I set it to do a long while back .

[britinusa]

Originally Posted by s/v Jedi

The problem isn’t that it happens, but the severity.

'Severity' I'm guessing is dependent upon the charging current at the time of a battery disconnect. Does that mean that reducing the charge rate will lessen the risk to the Alternator? If so, then any suggestion on the rate?

Not wanting to stray too far from the OP. Just looking to see if there is a simple solution, like reducing the charge rate for example.

Sure would be nice if the drop in battery makers would provide a pair of external connectors that are switched when the BMS is approaching shutdown so that it could be used to shut the Alternator down and avoid the issue ( of blowing the Alternator Diodes) eg. With a balmar MC 618 the alternator can be switched to Float mode by shorting the Battery #2 Temp sensor to ground just a short time before the battery shuts down.

[s/v Jedi]

Originally Posted by britinusa

'Severity' I'm guessing is dependent upon the charging current at the time of a battery disconnect. Does that mean that reducing the charge rate will lessen the risk to the Alternator? If so, then any suggestion on the rate?

Not wanting to stray too far from the OP. Just looking to see if there is a simple solution, like reducing the charge rate for example.

Sure would be nice if the drop in battery makers would provide a pair of external connectors that are switched when the BMS is approaching shutdown so that it could be used to shut the Alternator down and avoid the issue ( of blowing the Alternator Diodes) eg. With a balmar MC 618 the alternator can be switched to Float mode by shorting the Battery #2 Temp sensor to ground just a short time before the battery shuts down.

No, the simple solution is in the OP of this thread. When you use drop-in’s with no warning signal output, then you can’t charge straight from an alternator without dc-dc charger in between.

Lowering charge rate means the surge will be less severe, but the rectifier diodes are no match. I get the idea you want it cheap but safe? In that case, charge a lead acid start battery and use a Victron Smart Orion dc-dc charger: problem solved.

[newhaul]

Originally Posted by britinusa

'Severity' I'm guessing is dependent upon the charging current at the time of a battery disconnect. Does that mean that reducing the charge rate will lessen the risk to the Alternator? If so, then any suggestion on the rate?

Not wanting to stray too far from the OP. Just looking to see if there is a simple solution, like reducing the charge rate for example.

Sure would be nice if the drop in battery makers would provide a pair of external connectors that are switched when the BMS is approaching shutdown so that it could be used to shut the Alternator down and avoid the issue ( of blowing the Alternator Diodes) eg. With a balmar MC 618 the alternator can be switched to Float mode by shorting the Battery #2 Temp sensor to ground just a short time before the battery shuts down.

Simple solution is what I will be running when I get the new engine installed . A 75 amp stock internal regulator alternator and a 50 amp dc dc. From lead start battery to charge lifepo4 bank . no shutdown spike to worry about . after all we are sailboats and solar is a better recharging source than the iron wind. Cheaper in the long run to. That is where the lifepo4 acceptance rate really shines . basically no losses in efficiency till 99% .

[goboatingnow]

Most modern car alternators are these days compliant to SAE 1455 and equivalent iso load dump survival tests.

This means the alternator can survive a battery disconnect under power.

It’s easy enough to add additional surge protectors.

Given in lithium typically HVC disconnect will not be at full alt load the spike will normally be contained within the alternator.

However the issue is your cheap non automotive qualified devices connected to the alternator feed ( directly or indirectly )

To be automotive qualified these devices should equally be qualified to sae 1455 , the trouble is while car equipment typically is , marine electronics typically isn’t.

Hence the issue isn’t the alternator it’s the things connected to it.

[RaymondR]

Lead acid batteries exhibit both ohmic and reactive properties.

The ohmic properties are primarily expressed via the internal resistance of the battery, the reactive via the capacitance between the plates and may be as high as 1.5 farads in a 100 amp hour battery.

Which of these phenomena is responsible for the protection of the alternator connected to a lead acid battery subjected to rapid, partial load shedding?

If it is the reactive, ie primarily the capacitive, might not a large capacitor wired across the output of an alternator protect it from damage during rapid load shedding?

[goboatingnow]

Originally Posted by RaymondR

Lead acid batteries exhibit both ohmic and reactive properties.

The ohmic properties are primarily expressed via the internal resistance of the battery, the reactive via the capacitance between the plates and may be as high as 1.5 farads in a 100 amp hour battery.

Which of these phenomena is responsible for the protection of the alternator connected to a lead acid battery subjected to rapid, partial load shedding?

If it is the reactive, ie primarily the capacitive, might not a large capacitor wired across the output of an alternator protect it from damage during rapid load shedding?

No a real world large capacitor has both ohmic and inductive properties and makes a poor surge suppressor. A battery is a very complex item not easily modelled as a mere capacitor

For example large electrolytic caps look highly inductive to fast transients which is exactly what you don’t want.

[goboatingnow]

The solution to alternator disconnect a is pre warning shutdown . It’s easily added and cost effective

[rgleason]

Originally Posted by goboatingnow

Most modern car alternators are these days compliant to SAE 1455 and equivalent iso load dump survival tests.

This means the alternator can survive a battery disconnect under power.

It’s easy enough to add additional surge protectors.

Given in lithium typically HVC disconnect will not be at full alt load the spike will normally be contained within the alternator.

However the issue is your cheap non automotive qualified devices connected to the alternator feed ( directly or indirectly )

To be automotive qualified these devices should equally be qualified to sae 1455 , the trouble is while car equipment typically is , marine electronics typically isn’t.

Hence the issue isn’t the alternator it’s the things connected to it.

Sort of nutty, but perhaps idea is to connect the DC panel to the FLA Start to protect the marine equipment from the spikes, and Alt charge the LFP, with a DC-DC Converter charging the FLA?

Sure would be nice if the drop in battery makers would provide a pair of external connectors that are switched when the BMS is approaching shutdown so that it could be used to shut the Alternator down and avoid the issue ( of blowing the Alternator Diodes) eg. With a balmar MC 618 the alternator can be switched to Float mode by shorting the Battery #2 Temp sensor to ground just a short time before the battery shuts down

I agree and have always thought this would be the best solution for Dropin LFP in a marine environment. The problem is the manufacturers don't see the Marine Industry and Camper Vans using Alternators, rather than Solar, as a big segment. However the best way to shut down the alternator is to interrupt the field wire or or the brown ignition wire! Refer to Balmar notes.

I am interested in a simple device that will use Nick's (Jedi) suggestion (the topic of this thread) to accomplish the alt disconnect prior to BMS shutdown.

I know it is easy to program for some, and to make novel circuits and it is a trivial thing to do for some electrical engineers, but to most of us it is a learning experience and will not be attempted without proper instruction. Being visually oriented I would love to see a diagram of this, and offer to help, if I can get someone to review.


PS: This post is written with the intention of Charging LFP with the Alternator, not the DC-DC converter or only solar (which is another equally viable approach with its own pros and cons).

[goboatingnow]

Originally Posted by rgleason

Sort of nutty, but perhaps idea is to connect the DC panel to the FLA Start to protect the marine equipment from the spikes, and Alt charge the LFP, with a DC-DC Converter charging the FLA?


I agree and have always thought this would be the best solution for Dropin LFP in a marine environment. The problem is the manufacturers don't see the Marine Industry and Camper Vans using Alternators, rather than Solar, as a big segment. However the best way to shut down the alternator is to interrupt the field wire or or the brown ignition wire! Refer to Balmar notes.

I am interested in a simple device that will use Nick's (Jedi) suggestion (the topic of this thread) to accomplish the alt disconnect prior to BMS shutdown.

I know it is easy to program for some, and to make novel circuits and it is a trivial thing to do for some electrical engineers, but to most of us it is a learning experience and will not be attempted without proper instruction. Being visually oriented I would love to see a diagram of this, and offer to help, if I can get someone to review.


PS: This post is written with the intention of Charging LFP with the Alternator, not the DC-DC converter or only solar (which is another equally viable approach with its own pros and cons).

The charge LFP directly is great. You just need a suitable alternator controller. Typically this will also facilitate remote shutoff. Then a low cost small dc dc can charge the starter battery from the lithium.

[s/v Jedi]

Originally Posted by rgleason

Sort of nutty, but perhaps idea is to connect the DC panel to the FLA Start to protect the marine equipment from the spikes, and Alt charge the LFP, with a DC-DC Converter charging the FLA?


I agree and have always thought this would be the best solution for Dropin LFP in a marine environment. The problem is the manufacturers don't see the Marine Industry and Camper Vans using Alternators, rather than Solar, as a big segment. However the best way to shut down the alternator is to interrupt the field wire or or the brown ignition wire! Refer to Balmar notes.

I am interested in a simple device that will use Nick's (Jedi) suggestion (the topic of this thread) to accomplish the alt disconnect prior to BMS shutdown.

I know it is easy to program for some, and to make novel circuits and it is a trivial thing to do for some electrical engineers, but to most of us it is a learning experience and will not be attempted without proper instruction. Being visually oriented I would love to see a diagram of this, and offer to help, if I can get someone to review.


PS: This post is written with the intention of Charging LFP with the Alternator, not the DC-DC converter or only solar (which is another equally viable approach with its own pros and cons).

You can simply buy these for a couple bucks, like this one: https://www.amazon.com/DROK-0-01s-99.../dp/B07VLXR7Z1

When the cheap BMS switches the negative with MOSFET’s, you need to turn off the regulator immediately and turn off the main battery switch/solenoid a second or two later. The first thing can be done with a relay, routing the regulator ignition or +B wire via a normally open contact of the relay. You can use that same relay to trigger the module linked above that you program to switch a couple seconds later and use that output to turn the main battery switch off.

Alternatively, use two of these delay modules, triggered by BMS at the same time and set one to 0s or 0.1s and the other to 2s. They are so cheap that this can be cheaper than just a normal relay.

[s/v Jedi]

I find it strange that nobody wonders what size battery would be needed, i.e. does a 7Ah AGM battery like https://www.amazon.com/ML7-12-Batter.../dp/B00K8V30D0 absorb the surge?

A battery is simply the best device but people try anything to find something that can’t really replace, is much more prone to failure, has a shorter lifespan and is much more expensive. Just because they have this thing in their mind that every battery aboard must be lithium iron.

It’s like someone want everything pink: it’s not rational, it is an obsession with eliminating lead acid battery at any cost (except it must be done cheap hahaha)

[newhaul]

Originally Posted by s/v Jedi

I find it strange that nobody wonders what size battery would be needed, i.e. does a 7Ah AGM battery like https://www.amazon.com/ML7-12-Batter.../dp/B00K8V30D0 absorb the surge?

A battery is simply the best device but people try anything to find something that can’t really replace, is much more prone to failure, has a shorter lifespan and is much more expensive. Just because they have this thing in their mind that every battery aboard must be lithium iron.

It’s like someone want everything pink: it’s not rational, it is an obsession with eliminating lead acid battery at any cost (except it must be done cheap hahaha)

The smallest that will crank your engine.
For me a U1 does the job .
Don't think it matters just the chemistry. Matters .

[s/v Jedi]

Originally Posted by newhaul

The smallest that will crank your engine.
For me a U1 does the job .
Don't think it matters just the chemistry. Matters .

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.