1.5 yr out out replacement of AGM with "drop in" LiFePO4
Jan 18, 2021 1:50:08 GMT
Post by dbostrom on Jan 18, 2021 1:50:08 GMT
After doing yeoman service for some 6 years (in charter!) our Lifeline AGM batteries became a bit squishy. Time for renewal.
The replacement I'm describing was done a year and a half ago. It's my observation that sometimes we're too excited about a new project and report in very early, before problems emerge. Here I thought it better to wait for some experience with new kit before banging on about it.
We're probably all familiar with the advantages of more modern alternatives to AGM.
In particular, LiFePO4 (lithium-iron-phosphate) batteries offer a very significant advantage in usable capacity for a given weight and volume, an enormous benefit in longevity when faced with deep discharge. As well they are quite happy to sit around in a state of partial charge, as opposed to any lead-acid battery where sulfation is more or less constant whenever the battery is below nominal cell voltage. Critically for purposes where people cannot run away from them, compared to other lithium ion batteries LiFePO4 fail gracefully and do not become hazardously unstable if overcharged or depleted too far.
As expected, while waiting for our AGMs to die tremendous progress has been made in producing integrated LiFePO4 batteries that do not become an expensive science experiment.
Dragonfly builds "drop in" replacements for Group 31 batteries. These can be paralleled without hazards and are an exact fit for what they displace. Various terminal adapters are available. Physically the worst a person will face is if positive and negative terminals are opposite to the batteries being swapped out.
These batteries have extensive "intelligence" built in, including critical low voltage disconnect, overvoltage protection, thermal management and (most importantly in terms of longevity) per cell balancing.
Installation was easy, physically.
The slight twist: these batteries are unsuitable for starting/thruster/windlass operation. At the same time, they're best set up with constant voltage charging, at 14.4 volts.
Meanwhile of course AGMs held over for starting/thruster/windlass need babying during charge.
Prioritizing AGM (the only safe choice if there's a single charging source) means the LiFePO4 will not reach much above 80% charge. This won't harm them, but it's wasted capability.
How to square this circle? A tiny bit of complication. Not much.
The solution here was split charging duties. The alternator (via programmable Balmar regulator) handles the LiFePO4 batteries. A DC-DC intelligent charger (Renogy 40A) replenishes AGMs. Given the duty cycle of the AGMs, 40A is plenty. A relay controls operation of the DC-DC charger, with the charger being on and supplied by the domestic side when the engine is running. For layup periods while the boat is at the dock and plugged in for extended periods, a manual switch causes the same relay to connect the DC-DC charger.
Meanwhile, it turned out that our 10 year old Magnum inverter's control head could have a firmware upgrade done, making constant voltage an option. Hats off to Magnum.
Connections are provided to "fall back" to mixed mode in the case of the DC-DC charger failing.
Our experience with these has been excellent. By chance, twice during the last year and a half we've had guest crew go through all 300AH of capacity of the triplet, leave the boat at the dock disconnected and depleted. There is no difference in performance of the batteries from this experience which we know via testing by Practical Sailor and direct experience will leave a permanent mark on AGMs. Making batteries more robust in the hands of others. is one of the main issues I was hoping to tackle by modernization and we do seem to have a payoff in this dept.
Significantly less weight.
Voltage is nice and stiff throughout discharge. The discharge voltage curve is quite flat until near the very end of capacity, meaning electric heads, pumps etc. work enthusiastically regardless of SOC. This does mean some retraining is needed; with a oad of say 8-10A, terminal voltage for a nearly depleted bank will read at around 12.1 volts. This of course is different to our experience w/AGM and other lead-acid.
Mostly I'm happy to be done with batteries and not to be obsessing over twitchy lead-acid. Lifespan on these is approximately 3,000 cycles at 80% DOD. At 60%, lifespan reaches absurd levels. Unless there's a defect type failure (as opposed to wear), these should last until I'm in my grave. We shall see about that.
The downside? Only one: dollars. But in the year and half since I installed these units, their price has dropped from $1k each to $900. Meanwhile, there's arithmetic on amortized cost and as well "life is too short to be hassling with batteries" in the positive column. For me this wasn't a very hard choice. AGM have had their day in the sun.
IMPORTANT: If you contemplate following this road, you need to make absolutely sure your alternator is thermally protected either internally or by external regulator (for latter a temperature sensor must be present). Otherwise, you will fry your alternator. Charge acceptance on these is brutally high. if there are multiple copies connected and the alternator is "naked," it will overheat. As well and as always, not letting your engine compartment become too warm is a good idea. The box-ticker fan supplied with our boats is actually not really large enough for this job. (alternators are in the neighborhood of 50% efficiency, which means that a 100A alternator running at its rating must shed a copious amount of heat-- this needs relatively cool air in order to happen)
Photo: I have two blown spinal discs. I wouldn't be able to do this with AGM.
Installed batteries. There's not much drama-- it's just batteries, not science experiment (cables since shortened, cleaned up-- photo taken on a Friday during 4 hour availability between charters). The DC-DC charger is barely visible below the fuse block at lower left.
The replacement I'm describing was done a year and a half ago. It's my observation that sometimes we're too excited about a new project and report in very early, before problems emerge. Here I thought it better to wait for some experience with new kit before banging on about it.
We're probably all familiar with the advantages of more modern alternatives to AGM.
In particular, LiFePO4 (lithium-iron-phosphate) batteries offer a very significant advantage in usable capacity for a given weight and volume, an enormous benefit in longevity when faced with deep discharge. As well they are quite happy to sit around in a state of partial charge, as opposed to any lead-acid battery where sulfation is more or less constant whenever the battery is below nominal cell voltage. Critically for purposes where people cannot run away from them, compared to other lithium ion batteries LiFePO4 fail gracefully and do not become hazardously unstable if overcharged or depleted too far.
As expected, while waiting for our AGMs to die tremendous progress has been made in producing integrated LiFePO4 batteries that do not become an expensive science experiment.
Dragonfly builds "drop in" replacements for Group 31 batteries. These can be paralleled without hazards and are an exact fit for what they displace. Various terminal adapters are available. Physically the worst a person will face is if positive and negative terminals are opposite to the batteries being swapped out.
These batteries have extensive "intelligence" built in, including critical low voltage disconnect, overvoltage protection, thermal management and (most importantly in terms of longevity) per cell balancing.
Installation was easy, physically.
The slight twist: these batteries are unsuitable for starting/thruster/windlass operation. At the same time, they're best set up with constant voltage charging, at 14.4 volts.
Meanwhile of course AGMs held over for starting/thruster/windlass need babying during charge.
Prioritizing AGM (the only safe choice if there's a single charging source) means the LiFePO4 will not reach much above 80% charge. This won't harm them, but it's wasted capability.
How to square this circle? A tiny bit of complication. Not much.
The solution here was split charging duties. The alternator (via programmable Balmar regulator) handles the LiFePO4 batteries. A DC-DC intelligent charger (Renogy 40A) replenishes AGMs. Given the duty cycle of the AGMs, 40A is plenty. A relay controls operation of the DC-DC charger, with the charger being on and supplied by the domestic side when the engine is running. For layup periods while the boat is at the dock and plugged in for extended periods, a manual switch causes the same relay to connect the DC-DC charger.
Meanwhile, it turned out that our 10 year old Magnum inverter's control head could have a firmware upgrade done, making constant voltage an option. Hats off to Magnum.
Connections are provided to "fall back" to mixed mode in the case of the DC-DC charger failing.
Our experience with these has been excellent. By chance, twice during the last year and a half we've had guest crew go through all 300AH of capacity of the triplet, leave the boat at the dock disconnected and depleted. There is no difference in performance of the batteries from this experience which we know via testing by Practical Sailor and direct experience will leave a permanent mark on AGMs. Making batteries more robust in the hands of others. is one of the main issues I was hoping to tackle by modernization and we do seem to have a payoff in this dept.
Significantly less weight.
Voltage is nice and stiff throughout discharge. The discharge voltage curve is quite flat until near the very end of capacity, meaning electric heads, pumps etc. work enthusiastically regardless of SOC. This does mean some retraining is needed; with a oad of say 8-10A, terminal voltage for a nearly depleted bank will read at around 12.1 volts. This of course is different to our experience w/AGM and other lead-acid.
Mostly I'm happy to be done with batteries and not to be obsessing over twitchy lead-acid. Lifespan on these is approximately 3,000 cycles at 80% DOD. At 60%, lifespan reaches absurd levels. Unless there's a defect type failure (as opposed to wear), these should last until I'm in my grave. We shall see about that.
The downside? Only one: dollars. But in the year and half since I installed these units, their price has dropped from $1k each to $900. Meanwhile, there's arithmetic on amortized cost and as well "life is too short to be hassling with batteries" in the positive column. For me this wasn't a very hard choice. AGM have had their day in the sun.
IMPORTANT: If you contemplate following this road, you need to make absolutely sure your alternator is thermally protected either internally or by external regulator (for latter a temperature sensor must be present). Otherwise, you will fry your alternator. Charge acceptance on these is brutally high. if there are multiple copies connected and the alternator is "naked," it will overheat. As well and as always, not letting your engine compartment become too warm is a good idea. The box-ticker fan supplied with our boats is actually not really large enough for this job. (alternators are in the neighborhood of 50% efficiency, which means that a 100A alternator running at its rating must shed a copious amount of heat-- this needs relatively cool air in order to happen)
Photo: I have two blown spinal discs. I wouldn't be able to do this with AGM.
Installed batteries. There's not much drama-- it's just batteries, not science experiment (cables since shortened, cleaned up-- photo taken on a Friday during 4 hour availability between charters). The DC-DC charger is barely visible below the fuse block at lower left. 
