This sent me down a rabbit hole.
Have you guys looked into inverters with their own built in transfer switch?
Have you guys looked into inverters with their own built in transfer switch?
CK5
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Electrical system load measurements?
- Thread starter dyeager535
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Haven't really dealt with fitment issues, at this point ,my battery is standalone. But from the cheaper battery cut opens I've seen, it's as you describe, generally the interior has a lot of wasted space. There are some "mini" 100Ah batteries, but I don't know if they are made to conform to a specific form, or they just made the case smaller and called it good enough.
Inverter-wise, something along this route but 12V? https://www.dchousepower.com/products/48v-25a-lithium-battery-charger-2000w-pure-sine-wave-inverter
I used that one a bit, worked fine. I didn't stress it, but it worked as advertised in terms of charging, I didn't get close to trying to push the 2kw output, but 120V stuff worked fine that I did plug into it.
Seemingly decent inverters have gotten pretty reasonable price-wise. For $179 to my door (DCHouses ebay store) it was cheap enough that it felt like a good way to get my feet wet in inverters. I have grandiose visions of eventually getting a 240V inverter to run the house off the panel instead of a bunch of extension cords when the power goes out, but the cost/benefit doesn't really work out for me on that.
I haven't read all the responses, but you can get a pretty good idea of the electrical load using a voltmeter. Since all wires have resistance, if you measure the voltage drop from one end of the wire to the other you can divide that by the resistance of the wire and get the current. For example, if you have a 2AWG wire going from the battery to the starter that is 6 ft long the resistance of that wire will be 0.001518 ohms. The way you figure that out is to look up the resistance of the wire under test and it will tell you the ohms/foot (or ohms per 1000 feet). Then you multiply that number by the length of the wire to get your total resistance. Now measure the voltage drop from one end of the wire to the other. Say it's 0.1 volts. Knowing that voltage=current x resistance we can calculate the current. Let's rearrange that equation into the form we want so that current=voltage/resistance. So with a voltage drop of 0.1V divided by 0.001518 equals about 66 amps. Of course this will all depend on the accuracy of your meter when reading the voltage drop across the wire. Do this for all the wires coming off your battery and add the results together. If this is too confusing just post up all the voltage drops across the wires coming off your battery and the gauge and length of your wires and I'll do the calculations for you.
Appreciate the offer!
I actually bought a clamp ammeter that is supposed to read quick enough to see the peak when the motor starts cranking. I expected it would actually record peak current, but apparently it doesn't, so I needed another body to assist, and I didn't have one available. I may have an opportunity in a few months to do some of this stuff.
In terms of what really is important, I need to get the truck hot and see what temps the battery sees. 140* is pretty much the hard limit for lifepo4, so if it exceeds that in the standard battery position, that's a decision point. I'm sure that can be mitigated, but not sure I'd want to expend that sort of effort.
By the time I get to this, maybe the prices will go down more. It seems the BMS is the major driver for the price difference on the LifePo4's advertised as starters, so maybe time will drive that price down like it has cells.
At this stage I'm pretty sure even 300A will start it. I'll still check, but everything I've seen indicates 300A is on the high side for any of the small block starters. Rockauto's AC Delco Starters for this vintage trucks show 1.4-1.5Kw on the couple I checked, 125A.
Make sure you get plenty of extra capacity, the battery will lose a lot of it's performance in the winter, if its big enough, it won't matter, if its not, you'll need a jump start.
The mini usually uses a different type of cell. A standard will use cylindrical, like 18650, and mini will use a pouch. I would avoid mini unless it's the only way to fit what you need.
I've been passively looking at ones with a built-in ATS.
Mostly because if I just use them for select devices (rooftop AC, outlet on countertop for coffee maker and another one for the microwave) I will cover everything 120vac I care about. So like a 3000w for the rooftop AC (it takes about 1350) and a 2000w for the coffee maker and microwave.
The other option is to go with a whole-motorhome inverter and then put another ATS in line with the generator leg of the existing ATS. Then use a NC 120vac relay to turn off the charging takeoff on the power converter once the inverter 120vac output is lit. My Dad ended up with a power loop on his and doesn't understand why his Inverter freaks out.
I haven't really looked at whole house inverter or battery or anything yet. Mostly because our power is currently so cheap (~.10kwh) because I'm on a muni power system. If I had to pay the rates my employer charges I'd totally have a 10kw solar array in my yard.
Alright so if I was going to get a lifepo4 and abuse it, I'd try a redodo 50Ah 12V lifepo4. Of course I wouldnt because that would not be what it's designed for and it would void any warranty. This specific one because dimensionally it would fit the relatively small battery cutout in the lawn tractor, and at some point I saw it listed with a high amp draw rating for surge. It would work fine in the lawn tractor (I'm sure) but it's a very basic electrical system of course. It would probably get used a couple hours starting and mowing in the lawn tractor, after mowing for thirty minutes or so, the battery would show 100% SOC, indicating the charging system is ok with it.
Unfortunately I found out these redodo's don't use a BMS that will communicate with either the bat-bms or Overkill solar apps, which means I can't see the individual cell voltages. Battery has been showing odd state of charge (SOC) readings since I got it, not sure yet if it's a battery issue or the cells just needing to balance themselves, but I can't tell since I can't see their voltages. Oh well. It was a pretty affordable battery.
Today I needed to move the truck. Went to crank it over, and the old lead acid battery wouldn't do it. I immediately went into dream world, and without grabbing all the tools necessary to swap batteries, simply imagined what it would be like if I had a 50Ah lifepo4 that might have a BMS capable of starting an L31 short block with TPI, using a power master mini starter. Since I wouldn't do that, but anonymously received media of someone who had the exact same vehicle setup as I did, using the same battery, I figured I should share that here. I am told the highest the app reported being pulled from the battery during cranking was 1800 watts.
Here is the battery sitting in a squarebody. No lip to anchor it and the battery terminals are opposite which leads to issues with shorter cables:
Here is the battery it replaced on top of it:
Here is the engine starting up on the lifepo4 (can't recall if dead cold or not, doesn't really matter, starts the same either way):
Here is the apps data while it's idling after starting:
Finally, here is the heater (heavy duty heater option) on high with the vehicle off. Yes, the heater is wired up direct to battery. You can see the weird SOC readings that between idling and after engine shutdown, within the span of a couple minutes, the SOC is wildly different. I'm told it stabilized at 99% shortly afterwards. I can only speculate that one cell is hitting a lower voltage due to the massive drain from the starter and it takes awhile to "catch up" via balancing:
The vehicle didn't idle long with the hood shut, so the battery temp never got over 68*. Not sure what the temp would get to with continued use.
I am told it seems like the voltmeter needle fluctuates a bit at idle, but with a digital multimeter it shows the voltage swing to be only from about 13.6 to 13.9V. If the swings are bigger than those values, the meter probably isn't fast enough to catch them.
Video of the battery app during startup/idle:
Unfortunately I found out these redodo's don't use a BMS that will communicate with either the bat-bms or Overkill solar apps, which means I can't see the individual cell voltages. Battery has been showing odd state of charge (SOC) readings since I got it, not sure yet if it's a battery issue or the cells just needing to balance themselves, but I can't tell since I can't see their voltages. Oh well. It was a pretty affordable battery.
Today I needed to move the truck. Went to crank it over, and the old lead acid battery wouldn't do it. I immediately went into dream world, and without grabbing all the tools necessary to swap batteries, simply imagined what it would be like if I had a 50Ah lifepo4 that might have a BMS capable of starting an L31 short block with TPI, using a power master mini starter. Since I wouldn't do that, but anonymously received media of someone who had the exact same vehicle setup as I did, using the same battery, I figured I should share that here. I am told the highest the app reported being pulled from the battery during cranking was 1800 watts.
Here is the battery sitting in a squarebody. No lip to anchor it and the battery terminals are opposite which leads to issues with shorter cables:
Here is the battery it replaced on top of it:
Here is the engine starting up on the lifepo4 (can't recall if dead cold or not, doesn't really matter, starts the same either way):
Here is the apps data while it's idling after starting:
Finally, here is the heater (heavy duty heater option) on high with the vehicle off. Yes, the heater is wired up direct to battery. You can see the weird SOC readings that between idling and after engine shutdown, within the span of a couple minutes, the SOC is wildly different. I'm told it stabilized at 99% shortly afterwards. I can only speculate that one cell is hitting a lower voltage due to the massive drain from the starter and it takes awhile to "catch up" via balancing:
The vehicle didn't idle long with the hood shut, so the battery temp never got over 68*. Not sure what the temp would get to with continued use.
I am told it seems like the voltmeter needle fluctuates a bit at idle, but with a digital multimeter it shows the voltage swing to be only from about 13.6 to 13.9V. If the swings are bigger than those values, the meter probably isn't fast enough to catch them.
Video of the battery app during startup/idle:
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I dont think I'd recommend this specific battery for automotive use.
Looks like it has no problem with the lawn tractor...probably such a slow charge rate the BMS is happy.
Automotive though...with a CS130 alternator (other designs may respond differently), after a start the battery will pull 40A. It will eventually go into protect mode which means the battery stops charging. Vehicle runs fine, voltage is stable, but the battery doesn't seem to want to come back online. At least after ~30 minutes of driving. It will balance itself but that takes time. When it finally does balance it's around 30% SOC. Still no problem restarting the engine at that SOC, and it seems to charge better starting at that SOC, but who wants to let their rig idle for two hours to charge?
I suspect the small cells in the 50Ah battery are drawn down too hard on a large engine start which creates a significant cell imbalance immediately, unlike perhaps a 100Ah unit with its larger capacity cells. At upwards of 2400W (200A) shown for instantaneous current at startup, not many 12V lifepo4's are rated for that sort of draw.
A 100Ah battery is probably in the cards for testing. Larger cells may be the key. Then the question becomes will the 100Ah battery try and pull even more out of the alternator? If double, 80A would put the alternator at over 80% load at idle, figuring in the other electrical loads like ignition.
Looks like it has no problem with the lawn tractor...probably such a slow charge rate the BMS is happy.
Automotive though...with a CS130 alternator (other designs may respond differently), after a start the battery will pull 40A. It will eventually go into protect mode which means the battery stops charging. Vehicle runs fine, voltage is stable, but the battery doesn't seem to want to come back online. At least after ~30 minutes of driving. It will balance itself but that takes time. When it finally does balance it's around 30% SOC. Still no problem restarting the engine at that SOC, and it seems to charge better starting at that SOC, but who wants to let their rig idle for two hours to charge?
I suspect the small cells in the 50Ah battery are drawn down too hard on a large engine start which creates a significant cell imbalance immediately, unlike perhaps a 100Ah unit with its larger capacity cells. At upwards of 2400W (200A) shown for instantaneous current at startup, not many 12V lifepo4's are rated for that sort of draw.
A 100Ah battery is probably in the cards for testing. Larger cells may be the key. Then the question becomes will the 100Ah battery try and pull even more out of the alternator? If double, 80A would put the alternator at over 80% load at idle, figuring in the other electrical loads like ignition.
Iirc you need a dc to dc converter for Lifepo batteries on an automotive alternator system. Lifepo need 14.4v to be fully charged.
They do make batteries rated at 12.8V that are supposed to be drop-in replacements for lead acid (i.e. 4C @ 3.2V). Knowing what a problem load dump can be in a car, the fact the BMS can disconnect the battery at will makes me nervous. It's kind of similar with a DC-DC converter - is the battery really there to smooth out all of the automotive transients? If the only problem was voltage, you could bump it up with a diode on the sense line. The correct way to charge a lithium battery is constant current until it's up to 80% SoC or something like that, then constant voltage to finish it off. A modern car with current monitoring on the battery and ECM alternator control could do this easily, if programmed correctly. I don't know what you'll get with an old school internally regulated alternator. Probably best case is that you never reach a high SoC and you only use part of the capacity.
I've been eyeballing this for the motorhome but haven't been able to convince myself to hit the button:
I have 2 of those but not the metal case.
I have had them for a couple of years but I have not used them too much to test them.
I researched a while before I picked them though.
My "house batteries" are a pair of Group 27. The biggest watt-hour single battery I can fit in the hole is that metal case Eco-worthy 280ah. I can't fit the plastic case one fro Eco-worthy or most of the other Chinesium plastic case ones. I have enough room on the inside of the frame rail on the driver's side to put two more of these batteries (on that frame rail currently is the factory auxiliary battery and the pup and controls for the hydraulics).
Anyway, what reminded me of this thread is that I've been doing a lot of load measuring as I replace all my lead-acid batteries. I bought a lithium for my zeroturn mower and it's a bit of a POS but the charging system on a Kawasaki isn't great to begin with.
Anyway, what reminded me of this thread is that I've been doing a lot of load measuring as I replace all my lead-acid batteries. I bought a lithium for my zeroturn mower and it's a bit of a POS but the charging system on a Kawasaki isn't great to begin with.
Yes, that IMO is still a question as to how hard this is on the alternator over time. There doesn't seem to be a spike when the BMS disconnects, so I *think* that indicates the "base" load on the electrical system is enough to ensure a spike isn't occurring.
I haven't driven it long enough to know if the BMS will reconnect once cells are balanced while the vehicle remains running. Balancing seems to be a rather long process (many hours) so I'm not sure it would ever get to that point driving in any case.
I still don't quite understand why this battery acts as it does. The BMS seems very slow to report it's actual SOC. I have run it on my mower for a few hours now, and it never disconnects, charging at about 2A/13.4V while running. Finished up yesterday, battery was showing 99% SOC. Let it sit a few minutes, and then it showed 3%. Hooked it up to a dedicated LFP charger, and while the battery showed ~1A charge current, with a 25 hour charge time, the charger showed a fault. I think that's just a "wake" function. Anyway, now, maybe 20 hours later, battery is at 100% SOC. As I've said before, I think having a BMS that will talk with the BAT-BMS is nearly a requirement when something seems wrong or odd, without seeing individual cell voltages you are unable to really know what is going on inside the battery.
If there are more cells in a larger battery, I would presume that IF the load and charge current stay the same, the load shared by each cell would decrease, maybe leading to less of this SOC/balancing concern. But I suspect that given a 50Ah battery will pull 40A in the truck, a 100Ah may pull 80-90A, which is way too much for my alternator, and is probably pretty unhealthy for the battery. I'll try it out if I find a 100Ah that is what I want for the price I want.
There are definitely both OEM and aftermarket LFP starters out there, but unless you knew you'd get 10 years of hard use out of one (like winching, where you could run one battery only?), the $4-500 price range I've seen still doesn't pencil out over the long haul. And I doubt the aftermarket LFP starters are any different on their heat tolerance or charge current safe limits, so using them in an old rig would still introduce issues IMO.
As mentioned, with new systems where you can adjust how the alternator performs, it would probably be possible to use one of these within their design parameters. While I find using this battery outside of its design parameters interesting, without resolving the quirks it introduces, I don't see it being a good replacement for a lead acid starter. It will be a good jumper though.
I'll need to use it to start the truck, turn it off, and let it balance itself for a day or so to see how much is really being pulled out of it in a typical start, just to get an idea. I suspect it's around 5% each time. But that's a guess based on the draw I've seen while it cranks.
On the storage side, I've had my 48V 100Ah battery in use for a few months now. Within their design parameters, lead of any sort has no chance of competing. I wish I had more use for it daily.
FWIW, from what I've seen lately, now is not the time to buy LFP. Prices had been falling consistently, but lately they seem to have reversed pretty hard. I know a decent (key: decent) 12V 100Ah LFP was getting into the $150 range, but now I can't even find refurbished units at that price. And Bluetooth adds another cost to it, as well as heated versions. But I think I'd figure heating out myself. Not sure if it's tariffs or something else that's hit the prices as it has, but Im not in a big enough hurry to pay more for something that should be dropping in price.
Yeah they were dropping big time.
The 280ah that I bought for $450 on sale went down as low as $325 but recently they went back up to $450 range
I wouldn't be buying anything now.
There's a new shake up in the technology and 3 companies are making a sodium ion battery for sale as early as end of the year.
And they're supposed to last longer, charge faster and cost less
