mikefitz

Any voltage under 12v is less than 10% SOC. The cells used for the battery are not well matched ( cell imbalance is most pronounced at low voltage) and its probable that one cell went below the low volt cell protect, ( perhaps set at 2.5 volts), this would shut the BMS down. The DALY BMS may need a charge current over a certain value to 'wake up' that the Votronics unit may not provide. This feature of the DALY BMS may be a problem if you have a shutdown condition and are off grid. Some B2B chargers (Victron) have a power supply mode that would provide enough current. The Renogy products are being heavily promoted, but reports on USA forums indicate that there may be reliability issues and poor support from Renogy. Mike

Depending on the BMS settings, 0C disable and 5C enable may be set, thus the battery will need to warm to above 5C before the BMS activates the charge path. The battery should/will be able to provide power out if a current is drawn. The BMS will then activate the discharge path. Normally the BMS will/should allow discharge down to -20C. When the charge path is disabled and discharge is still allowed the BMS will only switch the discharge path 'on' if the current is above a certain value, ( around 0.5 amps). A multi- meter takes so little current you will 'see' a low voltage at the terminals. If may be useful to check the BMS settings for low temperature discharge disable, the battery should still be able to power the van circuits down to -20C. 13.1 volts and 86% SOC seem slightly out of sync. The Daly BMS used in Sterling batteries may give incorrect SOC readings. Mike

After reading through all the posts I have a number of suggestions. BMS settings. The BMS is a last resort protection device for the battery and in not intended to control charging, all charging devices should programmed to operate within the safe working area of the battery. The protection limits of 14.6 volts for the battery and 3.65 volts per cell voltage are considered safe limits. With balancing, this should occur only when the battery is under charge and in a high state of charge so needs to be over 3.4 volts per cell, Balancing start voltage = 3.4 volts Balance open difference volts = 0.015 volts. Thus balancing will not occur unless the voltage delta between cells is greater than 0.015 volts and the cell voltage is over 3.40 volts. Charger settings for lithium. Ideally the battery should be charge to almost full state of charge and then used. Where the battery is continually in a high state of charge service life is reduced. I have seen reports where lithium batteries lost considerable capacity within two years due to being continually under high charge and float voltages. Ideal charge voltage is 13.8 to 14.2 volts, 14 volts is a good compromise. Higher voltages will apply more stress to the battery. Float voltage should be set to the rest voltage of a fully charged battery, this will be 13.35 to 13.4 volts. A often used voltage of 13.8 volts will keep the battery fully charged and is not recommended. If the charger has a 're boost' setting this needs to be 0.1 volts lower than the float voltage. Sterling Batteries. Issues are being found on some batteries. BMS state of charge reporting. The DALY protection circuit, the BMS, does not report the SOC correctly and my also not report charge and discharge currents correctly. This is a known fault with the DALY BMS . I recommend you return the battery for a replacement. Cells with significant imbalance. Under charge some batteries have the charge path disconnected by the BMS when one cell goes over volts, that is exceeds the safe 3.65 volts across the cell. This should not happen despite what Sterling Technical tell you. The battery should be assembled with cells reasonable balanced before assembly. The BMS cell balancing is designed to compensate for small cell imbalance and cannot deal with this issue. If cell over volts stops the charge process then you have two problems, firstly the battery will never reach full capacity and secondly both the BMS and the cell are being over stressed. With the cell this results in accelerated capacity loss in that cell over time, and thus battery loss in capacity. If you find the battery is shutting down the charge current when under charge, ( the BMS will report a fault with cell over voltage), lower the charge voltage if possible. If the problem continues ask Sterling for a replacement battery. Sterling Batteries are excellent value however the quality control needs to be improved. Victron Battery Protect. There have been a considerable number of failures due to incorrect application of these units. This is partly a fault of Victron who did not stress that they are unidirectional and that they will also fail if subjected to excess over current. The Victron battery protect must not be connected between the battery and an inverter. The input capacitors in the inverter take a very large surge current that /will damage the Victron unit. Thus whilst using a Victron battery protect between the battery and consumers ( without an inverter) is OK, or between chargers and the battery, its not possible to use between the battery and an inverter/charger. Split charge and lithium batteries. With the low internal resistance of the lithium battery using a split charge is not recommended as a method of alternator charging. The only thing limiting the charge current is the resistance of the cables and components in the circuit charge path. A battery to battery charger is needed to safeguard the alternator and cables from damage and to ensure the lithium battery charge current is within specified limits and to terminate charging when the battery reaches a high SOC. The alternator used on most vans is not designed to deliver more that about 50 amps over the normal power needed for van electricals. It would be prudent to design the charging circuit to ensure this limit is not exceeded. Mike .

Quote, ' They are supposed to be direct on negative post. I have 3 to accommodate - B2B, mains charger and solar regulator. Could I put these on busbar too?' On a lead acid battery the negative post is connected to the lead plates, has a good thermal path to the battery core temperature and thus is an ideal mechanical ( and electrical) point to attach a single wire thermal probe. On a lithium battery the negative post is connected within the battery case to the output side of the BMS protection module by a cable. As such, its more likely to measure the temperature of the cable and BMS rather than the temperature of the cells that make up the battery. However they need to be connected somewhere if necessary to control the charge process, so connecting to the battery post is perhaps the better option rather than the buss bars. Lithium batteries do not need temperature compensation of the charge voltages so unless the chargers are using temperature monitoring for low temperature charge disable, ( less than 5C) or battery overheat ( over 45C), they are not needed. Mike

Its poor practice to have multiple connections at the battery posts. The ideal method is to use positive and negative buss bars, with a single short cable link to the battery post. https://www.12voltplanet.co.uk/4-point-positive-distribution-block-busbar.html Having multiple cable terminal connections on the battery post will over stress the post and lead to unreliable connections. Best practice is to have no more than 2 connections per stud. Its probable that the lithium battery installs are incorrectly fused. The BS standard for 12v systems in leisure vehicles requires suitable over current protection at the power sources, the batteries, for all cables connected . Lithium batteries under fault conditions can deliver very high currents, several thousand amps. Most available fuses do not have the necessary interrupt rating. With a 12v systen its recommended to use a MRMF, (cube fuse) as close to the battery positive post as practical, https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A Hopefully the BMS protection built into the battery will offer over current protection, but this is not guaranteed and depends on semiconductor circuits and fet switches to disconnect. Mike

No personal experience of Sterling batteries but they performed well in independent tests by a boating magazine and recorded a capacity in excess of the specification. https://www.pbo.co.uk/gear/lithium-batteries-for-boats-reviewed-12-of-the-best-lithium-boat-batteries-tested-62244/2 Sterlings own test against lead acid batteries under worst case conditions, I do have experience of lithium batteries in a RV application and confirm that they live up to expectations. Charge very quickly and deliver power at almost constant voltage until near empty. All lithium battery cells are made in China. There are degrees of quality in both the cells that make up the battery and the way the battery is assembled. To prevent the battery from user abuse, all are fitted with a battery protection circuit , often called a BMS, a battery management system. Depending on the battery, this BMS will have maximum allowable charge and discharge currents, so this must be taken into account when selecting a battery. A typical quality 100Ah battery will have a continuous charge current of 50 A, and a continuous discharge of 100 A. Most will offer a number of charge and discharge cycles at their maximum ratings in the region of 2000 cycles. Mike

Short answer is that its not practical idea. For an inverter to deliver 850 watts it will draw something like 80 amps from a 12v battery and a bit less if there is alternator charge. So connecting an inverter direct to the engine battery with the engine running, could be considered. If the existing VSR were to be updated to a 180A, unit with substantial cables to the leisure battery, then the inverter could be connected there. ( in any event I advise up rating from a 30A VSR.) Although taking 80 A from the alternator is possible, ( the OEM is rated at least to150A maximum), it could introduce reliability issues. Peugeot/Citroen provide a 50A fused circuit for the converters outlet, so this suggests that 50 A is an allowable value. All things considered I would not recommend having an inverter taking 80A from the alternator in this application. You could consider using an inverter configured for 110 v ac, that would halve the power taken by the heater ( the heater circuits would need some investigation to confirm there would be no undesired side effects). A water heater that could be operated from alternator power with least complexity is the Surecal heater with a 300 watt 12v heating element, https://www.surejust.co.uk/6-litre-12v-240v-motorhome-water-heater. Mike