It doesn't sound like a voltage issue to me. It could be the BMS doing its thing (but I am extremely new to Lithium research and haven't yet converted).

Are you able to measure the draw from the battery when flushing? I have just taken a look at my Jabasco manual and it will draw 25 amps when being flushed. An old pump can draw more and a pump starting under load can also draw more. Then if you combine the 2 maybe the system has reached the BMS limits.... AGMs can handle that extra load surprisingly well.

And if you have someone whom tends to swallow olive seeds and frequents your vessel then no amount of power is going to overcome that. And no, don't ask how I know that 🤔

Kryspen, the amp hours is the capacity, not the current. I'm learning about lithium batteries at present as getting into drones.

Can you tell us what the maximum discharge rate on your lithium batteries is please? It will be in Amps not Amp Hours

Your agm batteries are likely rated for cranking (i.e. turning over your motor) which means lots of amps.

Thinking more about my reply above, for those with the knowledge, would the BMS react and shut the system down before the (toilet) fuse blows?

Something odd here - of course. The 130 AH lithiums should be fine to run 25 amps, there should be no need to get three. The problem is somewhere else. It would help if we knew the type of Lithiums - maybe they are just bad batteries. I certainly know my Watt cycle 200AHs can deliver up to 100 amps as stated on the box - no worries with the anchor winch or inverter loads. Lithiums are great at running motors usually.

Maybe they didn't charge properly and are flat - the voltage curve on lithiums is really flat and hard to tell if they are depleted. If Kryspen has not updated the alternator then maybe this got fried initially and the lithiums didn't charge at all. Maybe take them home and charge one at home and try again.

I just read that there is solar too - so probably not charge - it could be a strange thing.

There are some anchor winches that do not like lithiums - Quicks IIRC. The electric motors are designed for less than 12 volts. So when connected up to lithiums (which don't do voltage drop like AGM or flooded) the motors get too HIGH a voltage. The Jabsco toilet may have some sort of voltage monitor to stop too HIGH a voltage running through it. Toilet wires are long and probably thin, so the voltage with the AGMs was probably about 11 volts and with lithiums it could be 13.5 still.

However AI tells me this will not be it, so maybe we are back to the lithiums and a shoddy BMS. When the connector is opened there could be a much hugher inrush current an the 25 amps pulled - maybe up to 50 or more for a microsecond. It would be a pretty terrible lithium not to be able to handle 100 amps, but if the BMS can only handle 40 amps, then the inrush current could certainly trip it - but what lithium would be so low in current delivery?

Kryspen could try putting another high load on the system - an inverter running something or the anchor winch. Do they work?

We need to know the specs of the battery and more about the system.

Kryspen said..

Today's chart - did use toilet ( no seeds 😁 ). Possibly BMS stop it
Battery is brand new installed in May - Powertech lithium 120ah each from Jaycar charged by victron DC DC charger, now with victron mppt 100/30 charging ok as display parameters.

I've lithiums and no problem powering my jabsco heads or my muir anchor winch. If the batteries went in, in May and its July you're having problems with the toilet, makes me wonder about length of time away from the boat, and whether its a heads problem independent of the batteries (ie just a coincidence). Assuming it's salt water flush, you can get salt build up around the impeller, if there's evaporation from the bowl while away for a long period. And/or the impeller can bind to the porcelain when not used for a lengthy period, or if it has been run dry. Best to put freshwater into the bowl and pump a little through when you're going to leave the head for a long time. I'd try running the jabsco directly off an AGM, and if its not turning willingly, pull it apart and make sure the impeller is OK. If it does turn willingly on the AGM, then that does suggest it is the new batteries, somehow. (BTW I'm assuming you've remembered to open the stopcocks etc 😉 and haven't got a blockage problem with a holding tank or somesuch)

Electric motors can cause nasty voltage and current spikes. The voltage spikes and back EMF spikes from an 12V electric motor can easily be more than 1000V. Google this "can i get 1kv spikes from a 12v dc electric motor" for explanation. If the manufacturer of the motor involved didn't take care of that (to save money by not fitting filter and spike suppression parts) that might be happening and causing the BMS to operate. You cannot see these spikes with a meter. Try some Jaycar LF1292 filters (about $17 for four) on the motor and battery wires. They clip on. Put them on the power wires right next to the toilet. And more on all your battery cables.

Kankama said..
Something odd here - of course. The 130 AH lithiums should be fine to run 25 amps, there should be no need to get three. The problem is somewhere else. It would help if we knew the type of Lithiums - maybe they are just bad batteries. I certainly know my Watt cycle 200AHs can deliver up to 100 amps as stated on the box - no worries with the anchor winch or inverter loads. Lithiums are great at running motors usually.

Maybe they didn't charge properly and are flat - the voltage curve on lithiums is really flat and hard to tell if they are depleted. If Kryspen has not updated the alternator then maybe this got fried initially and the lithiums didn't charge at all. Maybe take them home and charge one at home and try again.

I just read that there is solar too - so probably not charge - it could be a strange thing.

There are some anchor winches that do not like lithiums - Quicks IIRC. The electric motors are designed for less than 12 volts. So when connected up to lithiums (which don't do voltage drop like AGM or flooded) the motors get too HIGH a voltage. The Jabsco toilet may have some sort of voltage monitor to stop too HIGH a voltage running through it. Toilet wires are long and probably thin, so the voltage with the AGMs was probably about 11 volts and with lithiums it could be 13.5 still.

However AI tells me this will not be it, so maybe we are back to the lithiums and a shoddy BMS. When the connector is opened there could be a much hugher inrush current an the 25 amps pulled - maybe up to 50 or more for a microsecond. It would be a pretty terrible lithium not to be able to handle 100 amps, but if the BMS can only handle 40 amps, then the inrush current could certainly trip it - but what lithium would be so low in current delivery?

Kryspen could try putting another high load on the system - an inverter running something or the anchor winch. Do they work?

We need to know the specs of the battery and more about the system.

I did used inverter and there's no problem at all , it's 4000/8000 inverter, slight voltage drop but works ok ( used to power up my Watermaker.

Quixotic said..
I've lithiums and no problem powering my jabsco heads or my muir anchor winch. If the batteries went in, in May and its July you're having problems with the toilet, makes me wonder about length of time away from the boat, and whether its a heads problem independent of the batteries (ie just a coincidence). Assuming it's salt water flush, you can get salt build up around the impeller, if there's evaporation from the bowl while away for a long period. And/or the impeller can bind to the porcelain when not used for a lengthy period, or if it has been run dry. Best to put freshwater into the bowl and pump a little through when you're going to leave the head for a long time. I'd try running the jabsco directly off an AGM, and if its not turning willingly, pull it apart and make sure the impeller is OK. If it does turn willingly on the AGM, then that does suggest it is the new batteries, somehow. (BTW I'm assuming you've remembered to open the stopcocks etc 😉 and haven't got a blockage problem with a holding tank or somesuch)

Appreciate advice.
I live on my boat so there's no " away from boat ". Macerator pump pulled apart, inspected, all good. Lifting water with no problem.
After spending $ on lithium battery + victron DC DC charger + mppt I'm not going back to AGM or gell ( they are gone ).
I try upgrade wiring to 8wg size, maybe will help.