Advice Needed - Mixed AGM and lead acid - Bow Thruster and Start Batt's

Skag · Jul 21, 2024

Last time I used my thruster, it was weak and didn't make much noise like it used to. I found that the two group 31 AGM's in series providing 24V to the thruster were near dead. I have since traced down the wiring and found the two thruster batteries are connected to my group 27 flooded lead acid (FLA) starting batteries (also in series 24V) through an ACR. When at the dock, the FLA starting batteries are charged by a small two bank 20amp 12V charger and the ACR closes to charge the thruster AGM's. When underway my 24V/35amp alternator charges the start batteries and the ACR closes to charge the thruster AGM's. I suspect I may have damaged the AGM's by combining them with the FLA batteries - likely overcharging them?

Curious how others may have their thruster battery system arranged (type of batts, charging at dock, charging underway).

At this point, I need at least two thruster batteries, but am contemplating just going with lead acid to match the start bank as I think that would solve the potential damage issue (too high of charge voltage from the FLA charger). I'd prefer AGM as I would rather not have the acid/maintenance. Should I go with 4 new AGM's (thruster and engine start)? Or just buy lead acid for the thruster and call it done. If going AGM for both start and thruster, would I need an external voltage regulator for my 24V 35amp alternator? Reading through several posts I see that you can damage an AGM battery if charged as a FLA battery. Would a DC to DC charge controller solve the mismatch?

I also have a 600 AH of AGM's for my 12V house bank that when underway are charged from my Delco 22SI 145A alternator - wondering if i should proactively convert to external smart regulator.

Skag · Jul 22, 2024

Doing a some research..... seems like a DC to DC charger is the way to go (in place of the ACR) and leave the starting batteries as affordable flooded lead acid. 24V/35amp Alternator w/ internal regulator would charge the start batteries and then the DC to DC charger would provide three step charge to thruster AGM's. Victron Orion Tr DC-DC Charger 24/24-17, appears to be a decent solution. Anyone familiar with these? I think 17amps would be fine. I don't use my thruster much and when running my main engine, it runs for several hours. The Victron has the added benefit of bluetooth monitoring - I can see my voltage on both start and thruster banks.

tiltrider1 · Jul 22, 2024

Skag said:
Doing a some research..... seems like a DC to DC charger is the way to go (in place of the ACR) and leave the starting batteries as affordable flooded lead acid. 24V/35amp Alternator w/ internal regulator would charge the start batteries and then the DC to DC charger would provide three step charge to thruster AGM's. Victron Orion Tr DC-DC Charger 24/24-17, appears to be a decent solution. Anyone familiar with these? I think 17amps would be fine. I don't use my thruster much and when running my main engine, it runs for several hours. The Victron has the added benefit of bluetooth monitoring - I can see my voltage on both start and thruster banks.

DC to Dc chargers is the correct way to deal with mixed chemistry batteries. I use the Victron DC to Dc charger. It is programmable for all the different chemistries and you just Bluetooth it to your phone.

Skag · Jul 22, 2024

tiltrider1 said:
DC to Dc chargers is the correct way to deal with mixed chemistry batteries. I use the Victron DC to Dc charger. It is programmable for all the different chemistries and you just Bluetooth it to your phone.

Thanks for the reply. Cheers.

dhays · Jul 23, 2024

On my boat I have an engine start battery, genset start battery, thruster/windlass bank, and house bank. All charging sources go to my house bank, then DC to DC chargers charge the Engine start battery, the Genset start battery, and the thruster bank.

tiltrider1 · Jul 23, 2024

dhays said:
On my boat I have an engine start battery, genset start battery, thruster/windlass bank, and house bank. All charging sources go to my house bank, then DC to DC chargers charge the Engine start battery, the Genset start battery, and the thruster bank.

That is my preferred way of doing it.

Currently I do it a little differently due to convenience but ultimately I will end up here.

PhilPB · Jul 23, 2024

I have one ProNautic charger dedicated to the AGM thruster battery and another larger 3 bank Genius charger for engine start SLA, generator start SLA and Flooded house bank.

CharlieO. · Jul 23, 2024

I recently went with a dc 2 dc charger 12v 18amp. I have a single bank 20amp charger when hooked to shorepower. I noticed when plugged into shorepower and charging the start bank then through the DC 2 DC charger charging the aux battery, my 20 amp charger was running pretty hard and warm (near full output) I will most likely be buying a new charger that is dedicated to the aux battery when on shorepower.

SteveK · Jul 23, 2024

dhays said:
On my boat I have an engine start battery, genset start battery, thruster/windlass bank, and house bank. All charging sources go to my house bank, then DC to DC chargers charge the Engine start battery, the Genset start battery, and the thruster bank.

As long as the ALT/reg is charging the correct battery type, it is the way to go.
I do it in reverse as my ALT is FLA profile internal regulator.
DC2DC is great in either direction as it has the different profiles.

tiltrider1 · Jul 23, 2024

SteveK said:
As long as the ALT/reg is charging the correct battery type, it is the way to go.
I do it in reverse as my ALT is FLA profile internal regulator.
DC2DC is great in either direction as it has the different profiles.

This is how I am currently doing it until I am in the mood to spend the money for an appropriate external regulator that allows me to send the full 110 amps from alternators to the house bank. For now I am only passing 50 amps from the start battery to the house via dc to dc charger.

There is nothing wrong with either method but direct to house bank is more efficient.

luna · Jul 23, 2024

Skag said:
Last time I used my thruster, it was weak and didn't make much noise like it used to. I found that the two group 31 AGM's in series providing 24V to the thruster were near dead. I have since traced down the wiring and found the two thruster batteries are connected to my group 27 flooded lead acid (FLA) starting batteries (also in series 24V) through an ACR. When at the dock, the FLA starting batteries are charged by a small two bank 20amp 12V charger and the ACR closes to charge the thruster AGM's. When underway my 24V/35amp alternator charges the start batteries and the ACR closes to charge the thruster AGM's. I suspect I may have damaged the AGM's by combining them with the FLA batteries - likely overcharging them?

Curious how others may have their thruster battery system arranged (type of batts, charging at dock, charging underway).

At this point, I need at least two thruster batteries, but am contemplating just going with lead acid to match the start bank as I think that would solve the potential damage issue (too high of charge voltage from the FLA charger). I'd prefer AGM as I would rather not have the acid/maintenance. Should I go with 4 new AGM's (thruster and engine start)? Or just buy lead acid for the thruster and call it done. If going AGM for both start and thruster, would I need an external voltage regulator for my 24V 35amp alternator? Reading through several posts I see that you can damage an AGM battery if charged as a FLA battery. Would a DC to DC charge controller solve the mismatch?

I also have a 600 AH of AGM's for my 12V house bank that when underway are charged from my Delco 22SI 145A alternator - wondering if i should proactively convert to external smart regulator.

If you can find 2 Group 31 wet cell LA starting batteries I would be tempted to go there. Otherwise 2 of the same Group 27 wet cell LA start batteries that start your engines would do as long as you keep the ACR in place. Wire the ACR to open when the thruster is used. No DC2DC required.

Todays (actually about for the last 20 years) wet cell lead acid starting batteries use very little water despite being charged at up to 14.5 volts and kept on float voltage almost in perpetuity. The reason is that Calcium replaced Antimony in start batteries.

Antimony remains in use in wet cell Deep Cycle batteries and as a result they use water and can deliver more cycles.

My 6 Group 24 wet cell start batteries that power my 24 volt thruster and windlass are now 5 years old. I gave up checking the water level in year 3. They still work as new.
Probably time to check again!

Skag · Jul 24, 2024

Appreciate the input guys. I’ve started buying what I need. I’m going with the DC to DC Victron. However, before I buy the AGM batteries, has anyone considered using LiFePO4 batteries for their thruster? Quality AGM’s are expensive. This LiFePO4 Banshee battery (see link below) is about 50% more. I already bought a victron dc to dc charger and it will do LiFePO4 charge profile. This battery says it will deliver 1200 CCA.

Possibly could provide backup power to the start battery somehow as well. My house bank is 12V so I don’t have a backup should my start bank get drained (except running the gen to charge with 120V AC Charger). If I was trapped somewhere with no option I could always rewire two of the house batteries in series to crank over the big diesel. I’m just hitting the crack pipe this evening.

Deep Cycle Lithium Iron Marine Battery Group 31 LiFeP04 1200CCA

Navigate with confidence using our 31M Lithium Marine Battery. Specially designed for marine applications, it offers lightweight, high-efficiency power and is resilient in harsh sea conditions

bansheebatteries.com

tiltrider1 · Jul 25, 2024

Ok, who is going to be first to see if they are for real?

Skag · Jul 25, 2024

On Amazon right now for $680. Cmon go for it! Or if you guys crowd fund me, I'll take a chance and report out.

mvweebles · Jul 25, 2024

tiltrider1 said:
Ok, who is going to be first to see if they are for real?

Quite a bit more expensive ($1200) but from a reputable brand. There is some crap out there in the LFP market - no telling where Banshee fits in.

H8/Group-49 Lithium Car Battery

Antigravity H8/ Group-49 Hi-Power lightweight Lithium Automotive Battery with RE-START Technology. Replace lead/acid battery in Hi-Performance Cars

antigravitybatteries.com

Peter

ranger58sb · Jul 25, 2024

Skag said:
However, before I buy the AGM batteries, has anyone considered using LiFePO4 batteries for their thruster?

I looked at the possibility -- and there's a thread on it around here somewhere -- but our thruster's current requirements are 560A @ 24VDC for 4.5 mins, and I never found a lithium solution for that.

Ditto with starting batteries; we need 1400A@24VDC, and I didn't find lithium options for that either.

Stayed with 8D pairs, but changed to Lifeline AGMs. $$$$$, but seem to be working well.

-Chris

mvweebles · Jul 25, 2024

ranger58sb said:
I looked at the possibility -- and there's a thread on it around here somewhere -- but our thruster's current requirements are 560A @ 24VDC for 4.5 mins, and I never found a lithium solution for that.

Ditto with starting batteries; we need 1400A@24VDC, and I didn't find lithium options for that either.

Stayed with 8D pairs, but changed to Lifeline AGMs. $$$$$, but seem to be working well.

-Chris

I'm not recommending it, but on paper, a pair of the 80AH/12V Antigravity batteries I linked above would run your thrusters, and probably start your engine. 4-1/2 mins of thruster run (560A x 24V) would be around 1000W of power, or just over 42AH (24V). A series-pair of the AG batteries are rated at 24V/80AH and could deliver up to 4000 Cranking Amps (supposedly analogous to CCA). At $1349/ea, probably not a lot more than the Lifeline AGMs.

Peter

ranger58sb · Jul 25, 2024

mvweebles said:
I'm not recommending it, but on paper, a pair of the 80AH/12V Antigravity batteries I linked above would run your thrusters, and probably start your engine. 4-1/2 mins of thruster run (560A x 24V) would be around 1000W of power, or just over 42AH (24V). A series-pair of the AG batteries are rated at 24V/80AH and could deliver up to 4000 Cranking Amps (supposedly analogous to CCA). At $1349/ea, probably not a lot more than the Lifeline AGMs.

Peter

Thanks, interesting to know.

I'm also constrained a bit by the other two banks, one each for starting a main engine and then each also servicing about half of the house DC loads. I'm thinking 255 Ah from the AGM banks is decent, whereas it might take more shopping to solve that with lithium too.

And part of that is work-avoidance on my part, given splitting start functions away from house loads would take some study, and then some effort.

Another constraint is physical; each of our three large banks are kinda located in a reasonably logical place, each with a reasonably logical 2x8D footprint. Maybe not completely unchangeable, but alternatives haven't caught my attention yet.

And in the meantime, our systems seem to work well enough... and I've got other higher-pri things to mess with (aka fix) too... so the sleeping dog isn't bothering me too much.

-Chris

SteveK · Jul 25, 2024

Skag said:
Appreciate the input guys. I’ve started buying what I need. I’m going with the DC to DC Victron. However, before I buy the AGM batteries, has anyone considered using LiFePO4 batteries for their thruster? Quality AGM’s are expensive. This LiFePO4 Banshee battery (see link below) is about 50% more. I already bought a victron dc to dc charger and it will do LiFePO4 charge profile. This battery says it will deliver 1200 CCA.

Possibly could provide backup power to the start battery somehow as well. My house bank is 12V so I don’t have a backup should my start bank get drained (except running the gen to charge with 120V AC Charger). If I was trapped somewhere with no option I could always rewire two of the house batteries in series to crank over the big diesel. I’m just hitting the crack pipe this evening.

Deep Cycle Lithium Iron Marine Battery Group 31 LiFeP04 1200CCA

Navigate with confidence using our 31M Lithium Marine Battery. Specially designed for marine applications, it offers lightweight, high-efficiency power and is resilient in harsh sea conditions

bansheebatteries.com

OK, LFP for a house bank v. other FLA makes sense for more usable Ah. Where does it make sense to use an LFP start battery at double the cost of AGM for a short burst of energy required for starting. Dual purpose start/house is of no interest as we all have been separating these before LFP to ensure we have the ability to start.

tiltrider1 · Jul 25, 2024

mvweebles said:
Quite a bit more expensive ($1200) but from a reputable brand. There is some crap out there in the LFP market - no telling where Banshee fits in.

H8/Group-49 Lithium Car Battery

Antigravity H8/ Group-49 Hi-Power lightweight Lithium Automotive Battery with RE-START Technology. Replace lead/acid battery in Hi-Performance Cars

antigravitybatteries.com

Peter

My first concern here is that these are not LFP but some other lithium chemistry. I could not find any description other than Lithium-ion.

The only advantage of a LFP start battery would be the ability to combine house and start Bank for charging. Once invested in dc to dc chargers this becomes a Non issue. Except if the weight difference is critical for your boats speed performance.

The Banshee was listed as an LFP. I know nothing about there reputation.

mvweebles · Jul 25, 2024

tiltrider1 said:
My first concern here is that these are not LFP but some other lithium chemistry. I could not find any description other than Lithium-ion.

The only advantage of a LFP start battery would be the ability to combine house and start Bank for charging. Once invested in dc to dc chargers this becomes a Non issue. Except if the weight difference is critical for your boats speed performance.

The Banshee was listed as an LFP. I know nothing about there reputation.

The antigravity user manual states it is LiFePo4 chemistry, however it also stated that it should not be wired in parallel or series so ganging it for a larger or higher voltage bank is a no-go. This could be because antigravity has a unique feature - "Jump Start" where there is reserve power in the event you run down the base battery. But that's only a guess.

Running in the tropics with ambient temps well into the 90s (F), my engine room gets damn hot. Antigravity specs operating temp range of between 23F and 140F vs 122F for standard AGMs. While hot conditions raise the output of Lead Acid and AGMs, their life is seriously shortened when operated in hot conditions such as an engine room in the tropics. My AGM lasted 2-years of relatively light usage. The ability to comfortably operate in my engine room is reason enough to consider LFP even at $1k buy-in. Oh.....last year I had a Renogy DC-DC charger that charged my engine battery take a crap so adding a component isn't the panacea you'd think.

I'm not making any recommendations here - just speculating. I don't think we're too far from LFP for start batteries. Certainly with 5 years.

Peter

mvweebles · Jul 25, 2024

SteveK said:
OK, LFP for a house bank v. other FLA makes sense for more usable Ah. Where does it make sense to use an LFP start battery at double the cost of AGM for a short burst of energy required for starting. Dual purpose start/house is of no interest as we all have been separating these before LFP to ensure we have the ability to start.

I can imagine several use cases where a LFP start battery makes sense, and in some cases less expensive. As mentioned in my previous post, due to sustained low latitude cruising, my engine room gets hot - up to 115F; maybe mid/upper 80s when resting. I've made many runs of 48+ hours. That's damn hard on a traditional battery and has, in my opinion, led to relatively short life span of around 2-years did a marine G31 AGM at around $450/ea.

LFPs have several attributes which are meaningless for trawler start batteries (for example who cares about saving 40 lbs of ability to recharge quickly). But there are a couple attributes that pique my interest such as very low discharge rate, small footprint, can be mounted in any orientation, at least 5x cycle life, no DC-DC charger needed to confirm with LFP house bank, tolerates higher operating temps, lower voltage sag, etc. The last one - lower voltage sag - is especially important because it would allow a much smaller battery. Much of the reason lead-based start batteries are so big is to reduce voltage sag.

Again, this is all theory based on paper specs. I'm sure I'm not the only one with experience where what worked on paper was a miserable failure on real life. But in intrigued. There are definitely use cases for LFP start batteries in a boat.......if it works as described.

Peter

tiltrider1 · Jul 25, 2024

Well based on how information became available and how rapidly prices dropped on LFP, I am afraid to make a time guess on LFP start batteries.

Usually with technology you get some advantages but you pay more for the new technology. I didn’t see the need for LFP until the crazy price drops. Sure, there were advantages but they were nice to have, not necessary. Then suddenly I could have my cake and eat it to. All I had to do was find the appropriate way to install a LFP set up. Even that information has gone from scientific white papers to everyday knowledge over the last two years.

I will stay open minded on LFP start batteries and see what happens.

OldDan1943 · Aug 15, 2024

My opinion, don’t mix battery chemistry

Advice Needed - Mixed AGM and lead acid - Bow Thruster and Start Batt's

Veteran Member

Veteran Member

Guru

Veteran Member

Guru

Guru

Guru

Guru

Guru

Guru

Guru

Veteran Member

Guru

Veteran Member

Guru

Guru

Guru

Guru

Guru

Guru

Guru

Guru

Guru

Guru

Similar threads