Will these two solutions address two problems?

[ArmySailor]

My house bank consists of 2 x AGM batteries (180AH), my starter battery is 1 x AGM battery (60AH). I have the classic "off, 1, both, 2" switch. 1 is starter. 2 is house.

I'm considering the switch to lithium. There are two particular risks that keep jumping out at me. Can those smarter than me tell me if my solutions are nonviable?


problem 1) the BMS shutting of the charge once the lithium batteries are full
(result = spike which would damage alternator, etc)


2) overheating of the alternator, due to demands that lithium can put on an alternator for extended periods of time.


~

For number 1), will the following solution work? I can upgrade only my house bank, keep the starter battery as AGM. When starting / running the engine I will always have my switch on "BOTH". Will BMS cutoff induced spike still fry the alt?


For number 2) I would upgrade my old balmar MC-512 regulator to the MC-614-H, which from what I'm gathering can be programmed to keep the alternator within safe temperature limits.



There are two human error flaws here that put the system at risk
- I start the engine on "2" the house bank, lithium only, forgetting to put on "both". I'm happily motoring away on just "2" (lithium) and bam, BMS cut. No AGM to continue to take the charge from the alt.


- perhaps another human error, say that after motoring successfully on "both", I kill the engine and sail for 8 hours, forgetting to switch from "both" just to "2" and thus have both the starter and house batteries linked (which isn't good because then AGM and lithium are on the same circuit (?)



What else am I missing?

[smac999]

the bms does not shut of the battery when it's full. that is up to you to manage. it shuts off the battery if there is a problem.


a regulator with an alt temp sensor and the belt manager will help control the alt temp.

[SVQuestOfPaget]

I see a few potential design issues here. First, I would prefer a situation that eliminates the human error issues, but that's just personal preference. More importantly, your alternator can only be tuned/regulated to charge ONE TYPE of battery, either Lithium or AGM, but not both. Granted, your starter battery shouldn't ever need much in the way of topping up, but if you tune the charge parameters for Lithium, you'll be doing slow harm to the AGM.

The 614 Regulator can be tuned to dial back your alternator using the temp sensor and belt load manager. How big is your alternator to begin with?

Given your current setup, you could probably keep your existing regulator and charge the start battery directly. Then use a battery to battery charger from your start AGM to charge the Lithium bank. The charger will limit the current draw of the lithium bank to its given settings (20, 30, 40amp, etc. depending on the model you choose), so will keep your alternator from burning up.

In this installation, if or when the Lithium bank BMS reaches High Voltage Disconnect, it will not fry the alternator, as the B2B charger and starter battery provide the separation. You can wire the 1/2/B/O switch as a simple On/Off, and get a second On/Off switch in the starter battery positive line. This keeps both banks isolated from each other, except for the b2b charger, which only goes one way, and would be wired for Ignition On only. These are just some of the considerations to make with lithium, as the "drop in" batteries are anything but.

[ArmySailor]

I really appreciate the time you took to write this up. I'll circle back with a sketch another day. What you explained makes a lot of sense.

Thank you

Originally Posted by SVQuestOfPaget

I see a few potential design issues here. First, I would prefer a situation that eliminates the human error issues, but that's just personal preference. More importantly, your alternator can only be tuned/regulated to charge ONE TYPE of battery, either Lithium or AGM, but not both. Granted, your starter battery shouldn't ever need much in the way of topping up, but if you tune the charge parameters for Lithium, you'll be doing slow harm to the AGM.

The 614 Regulator can be tuned to dial back your alternator using the temp sensor and belt load manager. How big is your alternator to begin with?

Given your current setup, you could probably keep your existing regulator and charge the start battery directly. Then use a battery to battery charger from your start AGM to charge the Lithium bank. The charger will limit the current draw of the lithium bank to its given settings (20, 30, 40amp, etc. depending on the model you choose), so will keep your alternator from burning up.

In this installation, if or when the Lithium bank BMS reaches High Voltage Disconnect, it will not fry the alternator, as the B2B charger and starter battery provide the separation. You can wire the 1/2/B/O switch as a simple On/Off, and get a second On/Off switch in the starter battery positive line. This keeps both banks isolated from each other, except for the b2b charger, which only goes one way, and would be wired for Ignition On only. These are just some of the considerations to make with lithium, as the "drop in" batteries are anything but.

[fxykty]

Originally Posted by SVQuestOfPaget

I see a few potential design issues here. First, I would prefer a situation that eliminates the human error issues, but that's just personal preference. More importantly, your alternator can only be tuned/regulated to charge ONE TYPE of battery, either Lithium or AGM, but not both. Granted, your starter battery shouldn't ever need much in the way of topping up, but if you tune the charge parameters for Lithium, you'll be doing slow harm to the AGM.

The 614 Regulator can be tuned to dial back your alternator using the temp sensor and belt load manager. How big is your alternator to begin with?

Given your current setup, you could probably keep your existing regulator and charge the start battery directly. Then use a battery to battery charger from your start AGM to charge the Lithium bank. The charger will limit the current draw of the lithium bank to its given settings (20, 30, 40amp, etc. depending on the model you choose), so will keep your alternator from burning up.

In this installation, if or when the Lithium bank BMS reaches High Voltage Disconnect, it will not fry the alternator, as the B2B charger and starter battery provide the separation. You can wire the 1/2/B/O switch as a simple On/Off, and get a second On/Off switch in the starter battery positive line. This keeps both banks isolated from each other, except for the b2b charger, which only goes one way, and would be wired for Ignition On only. These are just some of the considerations to make with lithium, as the "drop in" batteries are anything but.

Agreed, don't rely on a manual switch - that's a guaranteed way to make a mistake.

Since the OP already has a Balmar 614 regulator, then the alternator can charge either the AGM start battery or the Lithium house battery. I would suggest sending the alternator charge to the Lithium bank as it will accept the alternator's charge much more efficiently than the AGM starter battery, and the 614 will manage the alternator to prevent the alternator over-heating or having too much belt load.

Regarding a high voltage disconnect, as long as the BMS sends a high voltage disconnect warning to the 614, the 614 will shut down the alternator gracefully and won't let it be fried. Any decent BMS will do this.

Then use a B2B charger to charge the start battery from the house battery. The B2B can be set so it only operates when the ignition is on, so you don't have to worry about drawing down the house battery.