Making a cheap BMS ABYC compliant

[wingssail]

Originally Posted by s/v Jedi

This thread explains how to do this without Arduino’s. Another forum member even reported that he had set it up like I described and it worked like a charm. That’s what it is about.

Not sure if you realize that I described how to connect a couple of relays, resistor and capacitor to a standard Daly BMS to make it work. May be you would join me in helping others and draw the diagram?

Do you realize that I have nothing to gain with this and do it in an effort to help people free of charge? It’s obvious I don’t need to hack a DalyBMS for myself. You come to every thread I start and start bashing instead of helping people, or describe how you are designing systems that will hit the market soon.

Well I personally liked your idea, not because I'd copy it exactly but because it presents a way of thinking which could work for me.

I'm in no hurry to install a Lithium battery system. I recognize their benefit but my existing system works fine. But next time I need to replace batteries
I'll pull the trigger, but in a cost effective way and a simple way, so an external BMS rigged to send alarms and triggers to my charging devices, is a real breakthrough for my thinking. Thank You

[s/v Jedi]

Originally Posted by RaymondR

How about this.

We use an alternator which has a battery voltage sensing terminal on the regulator and tie it into the lithium + terminal and use diodes to adjust tbe voltage sensed by the regulator. Then use large diodes in the LA battery charging circuit to suppress the max charging voltage. LA and lithium are charged in parallel and the BMS is left standard.

This means you are converting charge power from the alternator into heat instead of charging the battery. An ArgoFET is a much more efficient solution and the lifespan reduction from undercharging will be near unnoticeable.

[s/v Jedi]

Originally Posted by wingssail

Well I personally liked your idea, not because I'd copy it exactly but because it presents a way of thinking which could work for me.

I'm in no hurry to install a Lithium battery system. I recognize their benefit but my existing system works fine. But next time I need to replace batteries
I'll pull the trigger, but in a cost effective way and a simple way, so an external BMS rigged to send alarms and triggers to my charging devices, is a real breakthrough for my thinking. Thank You

We’re discussing all this alternator protection but with a lead acid start battery we can fix this easy using a battery isolator or a dc-dc converter. If your primary charging source is solar or a generator or shore power, then a dc-dc converter is the best option. If the primary charging source is the alternator, then the ArgoFET will be the winner.

In case people don’t want a lead acid start battery anymore, now you need an expensive BMS to shutdown the alternator regulator. Think $500-$1000 just for that BMS.

I know I’m keeping my Odyssey start batteries, because they outperform LFP options by magnitudes. For example, when I would short the output of my two group 31 start batteries, I get 10kA. That is 10,000A. When I do this with two LFP drop-in’s, I’m lucky to get 200A. That is the difference in output performance we’re talking about.
I just checked for an Amperetime 100A drop in… a popular choice. Everything they list is about use for a house battery, there is no mention of CCA or anything.

[RaymondR]

Originally Posted by s/v Jedi

This means you are converting charge power from the alternator into heat instead of charging the battery. An ArgoFET is a much more efficient solution and the lifespan reduction from undercharging will be near unnoticeable.

Whilst the voltage drop will create heat one must be mindful that since the LA battery is largely there as a transient suppressor and cranking an engine generally causes little discharge, the recharge current through the diodes will be of limited current and duration and consequently would not be significant.

Balanced against this is that diodes are generally very robust and low cost devices and a very simple circuit could be designed.

I'm a fairly regular used of MOSFETS and also more of a consumer of them than I should be due to a repeated failure to take proper precautions with them.

[goboatingnow]

Originally Posted by RaymondR

How about this.

We use an alternator which has a battery voltage sensing terminal on the regulator and tie it into the lithium + terminal and use diodes to adjust tbe voltage sensed by the regulator. Then use large diodes in the LA battery charging circuit to suppress the max charging voltage. LA and lithium are charged in parallel and the BMS is left standard.

Is there enough current flowing in the sense line to give predictable voltage drop. What’s the alternator set-point voltage normally set at.

[s/v Jedi]

Originally Posted by RaymondR

Whilst the voltage drop will create heat one must be mindful that since the LA battery is largely there as a transient suppressor and cranking an engine generally causes little discharge, the recharge current through the diodes will be of limited current and duration and consequently would not be significant.

Balanced against this is that diodes are generally very robust and low cost devices and a very simple circuit could be designed.

I'm a fairly regular used of MOSFETS and also more of a consumer of them than I should be due to a repeated failure to take proper precautions with them.

But you are trying to lower the charge voltage to the LA battery while it is already undercharged, worsening the situation. I can’t understand that, why make it worse?

[goboatingnow]

I don’t see the argument for a $1000 bms to start a engine. Fine todays cheap Chinese bms are not optimised for that. You could simply disable them to start the engine. Or I’ve no doubt we’ll see more multi purpose BMS in the future anyway

Getting rid of the starter would be a real saving in real estate and wiring to boot.

[goboatingnow]

Originally Posted by s/v Jedi

But you are trying to lower the charge voltage to the LA battery while it is already undercharged, worsening the situation. I can’t understand that, why make it worse?

My understanding is the diodes are on the voltage sensing terminal. There’s little current hence no heat

[newhaul]

Originally Posted by goboatingnow

I don’t see the argument for a $1000 bms to start a engine. Fine todays cheap Chinese bms are not optimised for that. You could simply disable them to start the engine. Or I’ve no doubt we’ll see more multi purpose BMS in the future anyway

Getting rid of the starter would be a real saving in real estate and wiring to boot.

Question
Get rid of what wiring? You still need a positive to the starter and a negative cable to the engine .
As to real-estate well I have to say what room will be gained ? A grp 24 doesn't take up that much space.
Disabling / bypassing the bms is not allowed by your exalted ISO.
So what you are saying is you don't care about the rules.
Welcome to the real world.

[goboatingnow]

Originally Posted by newhaul

Question

Get rid of what wiring? You still need a positive to the starter and a negative cable to the engine .

As to real-estate well I have to say what room will be gained ? A grp 24 doesn't take up that much space.

Disabling / bypassing the bms is not allowed by your exalted ISO.

So what you are saying is you don't care about the rules.

Welcome to the real world.

I can save a diode splitter , fuses , a starter battery monitor , a full battery space and tie downs and lead acid weight . The gains are small but material.

I can reprogramme the bms to allow starter currents etc.

I’ve repeatedly said that DIY compliance To ABYC or ISO is currently futile. ISO has no legal standing currently and ABYC Is advisory.

The issue here is the insurers , hence currently I suspect most diy LFP have little or no insurance cover in reality.

In my case my insurers are involved in approving the final system solution , standard lithium compliance does not arise in Europe as there is no legal basis for it.there are no certified professionals in this field either.

My view is to question why each component of the system exists and it’s justification. Given my LFP 100AH can start the engine and I have three of them proposed , I see no reason to have a fourth lead acid essentially doing nothing ( ie dead lead as someone said )

Sure some may recoil in horror at the prospect of no SLA starter. But I see little or no technical justification. I’m open to a reasoned debate.

[newhaul]

Originally Posted by goboatingnow

I can save a diode splitter , fuses , a starter battery monitor , a full battery space and tie downs and lead acid weight . The gains are small but material.

I can reprogramme the bms to allow starter currents etc.

I’ve repeatedly said that DIY compliance To ABYC or ISO is currently futile. ISO has no legal standing currently and ABYC Is advisory.

The issue here is the insurers , hence currently I suspect most diy LFP have little or no insurance cover in reality.

In my case my insurers are involved in approving the final system solution , standard lithium compliance does not arise in Europe as there is no legal basis for it.there are no certified professionals in this field either.

My view is to question why each component of the system exists and it’s justification. Given my LFP 100AH can start the engine and I have three of them proposed , I see no reason to have a fourth lead acid essentially doing nothing ( ie dead lead as someone said )

Sure some may recoil in horror at the prospect of no SLA starter. But I see little or no technical justification. I’m open to a reasoned debate.

Diode splitter?
One fuse? For what?
Why do you even want a battery monitor specific to a start battery? Either it works or it doesn't.
The gains are insignificant including the 35 pounds the battery weighs.
Now the safety improvement yes that is significant .
( any sailboat that goes offshore will experience at least one knockdown. )

[goboatingnow]

Originally Posted by newhaul

Diode splitter?

One fuse? For what?

Why do you even want a battery monitor specific to a start battery? Either it works or it doesn't.

The gains are insignificant including the 35 pounds the battery weighs.

Now the safety improvement yes that is significant .

( any sailboat that goes offshore will experience at least one knockdown. )

Everything on the boat is instrumented that includes the starter. It’s Soc is tracked and logged if required.

Again these are what’s present and what would become redundant if the LA starter was removed.

I agree the 3xLFP system with anyone capable of starting the engine and a backup small portable LI NMC jump starter makes. the system very reliable and safe.

[newhaul]

Originally Posted by goboatingnow

Everything on the boat is instrumented that includes the starter. It’s Soc is tracked and logged if required.

Again these are what’s present and what would become redundant if the LA starter was removed.

I agree the 3xLFP system with anyone capable of starting the engine and a backup small portable LI NMC jump starter makes. the system very reliable and safe.

We all understand your micromanagement style but specificly
Why a diode splitter ?
Why a fuse for the starter ?
Doesn't the solenoid negate that ?

[goboatingnow]

Originally Posted by newhaul

We all understand your micromanagement style but specificly
Why a diode splitter ?
Why a fuse for the starter ?
Doesn't the solenoid negate that ?

I have a diode splitter for the alternator and mppt controller as they both charge both domestics and starter.
( it’s a actually an ideal diode splitter )

Every battery lead is fused including the starter

[rgleason]

This is a good idea, but the BMS you referenced only supports

"Discharging current: 30A, Charging current: 15"
although this particular one is 48v is it enough for a decent sized alternator?


I am wondering what the best way to actually implement this is, perhaps for 12vdc

Originally Posted by s/v Jedi

Just a heads up for those worried about their alternator getting fried, or insurance demanding ABYC compliance:

I looked at the cheapest Daly Smart BMS for an 8s 24V strings of cells. This is a 30A version with Bluetooth and an app that allows configuration and full details of what is going on inside the battery. Here is a link: https://www.amazon.com/Protection-Bl.../dp/B09YNZP9MZ
These BMS’s are MOSFET based: the battery negative connects to the BMS and the BMS provides another negative to be used by the boat’s electrical system.

You can easily hack this:

1. From the positive terminal of the battery, connect first a class T fuse, then a Blue Sea Systems remote battery switch, then to the main positive busbar.

2. From the negative terminal of the battery, connect a direct cable to the main negative terminal, skipping the BMS.

3. Connect the BMS B- cable to the battery negative as well.

4. Connect the BMS cell balance leads to the battery cells.

Now you have everything connected except for the P- cable. You can connect to the BMS with their Bluetooth app and set everything up as you wish. Whenever the BMS determines everything is fine, the P- cable is connected to battery negative. When the BMS wants the battery to switch off, it disconnects the P- cable from battery negative.

All one has to do is create a mechanism to convert this signal of P- disconnecting from battery negative into what you want: which is first disabling chargers and or hight loads, then a couple seconds later, send a disconnect pulse to the Blue Sea systems RBS to disconnect the battery. This mechanism can be done old school, with relays, fly-back diodes and a time delay and pulse circuit or a little more refined using a microcontroller, relay for the warning signal and a little transistor to turn the RBS off. Anyone with a little Arduino experience can do this, even with an ATTiny.

Daly also sells a similar BMS for dual bus: instead of the single P- output, it also has a C- output, which is the negative for charge sources. This is even better because with that extra signal you can create separate warning outputs for stopping charging and stopping discharging.

All the above without opening up and modifying the BMS