Steve, Are you suggesting that even for like batteries in closed loop, that you would add 20 minutes per paralleled battery of absorb time? This is much longer than what I have understood various manufacturers to state. Thanks for your input. Howie Michaelson
On Mon, Jul 14, 2025 at 10:33 AM Steve Higgins via RE-wrenches < [email protected]> wrote: > Each battery has its own internal resistance. The higher the resistance, > the longer it takes to charge. The issue is that chargers are > voltage-based, and when charging multiple batteries in parallel, the > lower-resistance batteries reach the target voltage sooner than the > higher-resistance batteries. These lower resistance batteries cause the > voltage-based chargers to bypass the absorb stage, and this prevents the > batteries that are a bit low and out of balance from achieving that voltage > target. > > If your charger isn't a 2-stage charger, or you aren't holding the > absorb timer long enough, or the charger is a "Smart Charger" and it can be > made to think that the batteries are fully charged when they are not. > > The best way to avoid this: > > Wire parallel connections using positive/negative bus bars with > equal-sized cabling. Do not parallel LFP batteries with only cables, and do > not use the connections on the battery as a parallel connection. > > Use a charger that can be programmed for 2-stage charging. Unfortunately, > there aren't many of these out there... > > If you can't use a charger that operates in 2 Stage, you need to extend > the absorb timers so the charger is supplying voltage to the BMSs of the > parallel batteries, so all batteries have time to get to full balance. We > typically suggest 20-30 minutes of absorption time per parallel-connected > battery up to about 3 to 4 hours. For that bank with 10 batteries, I > would set the absorb timers to at least four, if not five, hours. > > You should also disable any end amp/return amp settings, as these are > often not programmed with a time delay and will result in the charger > bypassing the absorption timer. > > In general, the more the customer works with the bank, the more often > they'll have to balance. > > I would start by checking SOCs and Voltages every 90 days. If you notice a > difference of more than 0.3 volts or a spread of more than 4-5% points, I > would separate each parallel battery and boost each battery at Bulk/Abs > Voltage for at least one hour of abs time. Suppose the bank is way out of > balance. In that case, it may take a few cycles(6-10) to achieve that > balance, even so if it's been out of balance for a long time, you may never > again achieve full balacne, in those cases I would manually balance more > often every 1-2 months instead of 6-12 months. > > > > *Steve Higgins* *⋅* *Technical Services Manager* > *t* +1.902.597.4020 *m* +1.206.790.5840 > *f* +1.902.597.8447 *e* [email protected] > ------------------------------ > CONFIDENTIALITY: The information transmitted herein is intended only for > the addressee and may contain confidential, proprietary and/or privileged > material. Any unauthorized review, distribution or other use of or the > taking of any action in reliance upon this information is prohibited. If > you receive this email in error, please contact the sender and delete or > destroy this message and all copies. > ------------------------------ > > > > > On Mon, Jul 14, 2025 at 6:54 AM jay via RE-wrenches < > [email protected]> wrote: > >> Hi Steve, >> >> Maybe you can elaborate as to how this could happen. >> >> Let’s say all the batteries are designed for a 57.4 usual charge voltage >> with an acceptance range of around 56-58.4v. >> >> If you’re charging 10 batteries to 57.4v, the most that any one battery >> gets to is 57.4. If one gets full before others then it stops accepting >> charge, but at no point in the system does any battery see more than 57.4. >> >> Iv’e seen this with same 10 batteries all from one OEM all in one system, >> all new. They get off just a little and some take longer or shorter to >> charge fully to 100% but the voltage never rises above what the inverter or >> CC is set to. I don’t understand how this would cause damage or issue. >> >> >> >> thanks >> >> jay >> >> >> >> On Jul 14, 2025, at 7:46 AM, Steve Higgins via RE-wrenches < >> [email protected]> wrote: >> >> I wouldn't do it... By doing so, you'll likely void any manufacturer's >> warranty. >> >> If you must do it, I would manually balance the old/new banks every 60-90 >> days. This involves separating the parallel strings of batteries and >> charging each string independently to achieve a full charge. If you don't >> do this, the different ages can cause imbalances, which will lead to >> problems with the BMS, regardless of whether it is in open-loop or >> closed-loop configuration. >> >> >> >> *Steve Higgins* *⋅* *Technical Services Manager* >> *t* +1.902.597.4020 *m* +1.206.790.5840 >> *f* +1.902.597.8447 *e* [email protected] >> ------------------------------ >> CONFIDENTIALITY: The information transmitted herein is intended only for >> the addressee and may contain confidential, proprietary and/or privileged >> material. Any unauthorized review, distribution or other use of or the >> taking of any action in reliance upon this information is prohibited. If >> you receive this email in error, please contact the sender and delete or >> destroy this message and all copies. >> ------------------------------ >> >> >> >> On Mon, Jul 14, 2025 at 4:09 AM Jason Szumlanski via RE-wrenches < >> [email protected]> wrote: >> >>> There are never-ending videos on YouTube showing different brands and >>> capacities of LFP batteries working in parallel. I have never tried it >>> myself, and every instinct says don't do it, but I have a situation where >>> it would be very helpful. >>> >>> I have a client with an older 60 kWh battery that is discontinued and >>> incompatible with any other battery from the same manufacturer. It has a >>> BMS with a 51.2 volt nominal rating. They need another 20 kWh of capacity. >>> It is too costly to scrap the existing battery and start over, and the >>> existing battery has been tested and confirmed to hold very close to its >>> rated capacity. >>> >>> What is the real deal on mixing and matching? Is anyone doing this >>> safely and successfully? I wonder what the battery manufacturers say about >>> it. >>> >>> Jason Szumlanski >>> Florida Solar Design Group >>> _______________________________________________ >>> List sponsored by Redwood Alliance >>> >>> Pay optional member dues here: http://re-wrenches.org >>> >>> List Address: [email protected] >>> >>> Change listserver email address & settings: >>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >>> >>> There are two list archives for searching. When one doesn't work, try >>> the other: >>> https://www.mail-archive.com/[email protected]/ >>> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org >>> >>> List rules & etiquette: >>> http://www.re-wrenches.org/etiquette.htm >>> >>> Check out or update participant bios: >>> http://www.members.re-wrenches.org >>> >>> _______________________________________________ >> List sponsored by Redwood Alliance >> >> Pay optional member dues here: http://re-wrenches.org >> >> List Address: [email protected] >> >> Change listserver email address & settings: >> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >> >> There are two list archives for searching. When one doesn't work, try the >> other: >> https://www.mail-archive.com/[email protected]/ >> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org >> >> List rules & etiquette: >> http://www.re-wrenches.org/etiquette.htm >> >> Check out or update participant bios: >> http://www.members.re-wrenches.org >> >> >> _______________________________________________ >> List sponsored by Redwood Alliance >> >> Pay optional member dues here: http://re-wrenches.org >> >> List Address: [email protected] >> >> Change listserver email address & settings: >> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >> >> There are two list archives for searching. When one doesn't work, try the >> other: >> https://www.mail-archive.com/[email protected]/ >> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org >> >> List rules & etiquette: >> http://www.re-wrenches.org/etiquette.htm >> >> Check out or update participant bios: >> http://www.members.re-wrenches.org >> >> _______________________________________________ > List sponsored by Redwood Alliance > > Pay optional member dues here: http://re-wrenches.org > > List Address: [email protected] > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > There are two list archives for searching. When one doesn't work, try the > other: > https://www.mail-archive.com/[email protected]/ > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > http://www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > http://www.members.re-wrenches.org > >
_______________________________________________ List sponsored by Redwood Alliance Pay optional member dues here: http://re-wrenches.org List Address: [email protected] Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org There are two list archives for searching. When one doesn't work, try the other: https://www.mail-archive.com/[email protected]/ http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: http://www.re-wrenches.org/etiquette.htm Check out or update participant bios: http://www.members.re-wrenches.org
