Daly BMS died. Can I use the battery without a BMS for a short trip?

[coltfred]

The title pretty much says it all, but to give details.

I have a battery made up of 8 280ah eve cells, all ordered at the same time. It's running in a 2P 4S configuration. I was running a 250a Daly BMS that has gone belly up. This battery is in a van and is charged via a 60a DC to DC charger and a 30a solar charger. I have a manual shutoff switch that I can use to stop charging if I need to. I have a week long trip that starts next week and I could not get a new BMS in time because of the chinese new year.

Can I run the battery without one by just hooking to the positive and negative terminals? I assume I would need to manage the charging status of the battery myself (which I can do based on a Victron monitor that's keeping track of power in and power out).

Please let me know if this is possible and if it is, what I should watch out for.

I will not be buying a Daly BMS again, that's for sure.

 

[yodamota]

yes you can do this. I would charge at lower voltages say 13.8 absorb, and float at 13.2 or something. Keep the discharge low. You basically have no protection in-case something goes sideways.

 

[AntronX]

Can be done, depends on how meticulous you are. Limit charge voltage to 3.4v per cell or 13.6v total in both your dc-dc and solar cc to leave some safety headroom in case cells get unbalanced. Limit discharge voltage to 3.2v or 12.8v in your inverter. Monitor cell voltages manually with multi meter when batteries get near full and near empty.

 

[coltfred]

I don't know that I can change the charging voltages of my DC-DC or Solar. I'm using this dc-dc this solar charge controller. I'll look into how to control them.

I can easily shutoff the charging and limit discharging though as I have a master shutoff for disabling all charging. So I can keep the battery from being too close to 100% if that makes it safer.

 

[AntronX]

I don't know that I can change the charging voltages of my DC-DC or Solar

You can. Download user manual for both devices and follow instructions how to change voltages. Looks like closest voltage to 13.6v in dc-dc can only be set to 14V which is not ideal but is better than nothing.

 

[coltfred]

You can. Download user manual for both devices and follow instructions how to change voltages. Looks like closest voltage to 13.6v in dc-dc can only be set to 14V which is not ideal but is better than nothing.

Will do. Other than trying to charge slowly and not discharging too quickly is there anything else I should be worried about? I have the master switch to stop charging all together if the battery should be full. Should I use that to stop all current in and out when it's full?

I really appreciate the information. Thanks!

 

[Rocketman]

If your system has been running just fine for a while - yes you can. Especially if you make it even more conservative (like others here have suggested).

I did the same thing on my system for about 2 weeks. (I can’t blame my bms supplier - battery acid does bad things to electronics).

Just get a new good one in soon.

 

[Skypower]

Like others have said, yes you can but I’d like to add that you may want to check how good the balance is at absorb voltage. If it’s good you may have at least a half dozen cycles before you need to intervene, but I’d still recommend periodic monitoring. This is very temporary so you need to get a new one on order today and put up reminders for the replacement. You are not protected if SHTF

 

[coltfred]

You can. Download user manual for both devices and follow instructions how to change voltages. Looks like closest voltage to 13.6v in dc-dc can only be set to 14V which is not ideal but is better than nothing.

This is a screenshot of the renogy BT app. I assume I should change the boost charge volt, float charge volt and equalize charge volt? The settings recommended above were 13.2 for the float and probably just set the other 2 to 13.6?

I saw there were some normal recommended settings over in this thread. Appreciate any information. For now I've just disconnected the battery all together until I figure out the correct settings.

 

[AntronX]

Set HV disc to 14V; Charge limit, equalize, boost, float to 13.6V; Low V alarm to 12.4; Over disch, disch limit to 12V. This is only because you don't have BMS to protect battery for you.

 

[Bop]

I have been running my 'temporary' 12v bank (16x 400Ah cell in 4S4P) without a balancer for nearly three years now and even after all that time, I have not had to do a manual rebalance once...
(Yes I know you shouldn't, but my BMS is a 16 cell 48v one for the house, but in the shed it is running at 12v for the caravan- plus I have the gear to do a single cell balance manually... do as I say, not as I do lol)

The first month I did daily checks to make sure it was going to be ok, then after a while went to weekly checks, now its once a month

As people have said- the trick is to stay out of BOTH ends of the charging/discharging curves- I don't go above 14v while charging, and low voltage cutoff is at 12v (my LYP cells are rated 2.8v to 4v, thats 11.2v maximum discharge voltage and 16v maximum charge voltage)- it is the top and bottom 20% that are the 'killers' when it comes to cells getting out of balance, so by staying well out of them, its not been an issue to date...

It does lose me a little bit of the 'theory' capacity, but the van doesn't load this bank hardly at all (most nights I drop from 13.15v offcharge down to 12.9v to 13v overnight even with the ceiling fan in the van running all night- even in winter when I run the electric blanket all night, it has never dropped down below 12.8v...

(yes the caravan has a 12v ceiling fan in it in the bedroom lol- just don't stretch up too high in the mornings!!!)

(yes I know the roof hatch looks tatty- but then this caravan is over 50 years old!!!- 1972 26ft Viscount...)

 

[sunshine_eggo]

get and install this (you'll need to get a 4S JST harness and make your own terminals):

Amazon.com

You can see your cells, and it can balance a wee bit.

or install one of these on each cell:

https://www.amazon.com/Sumklin-Voltmeter-2-5-30V-Voltage-Combined/dp/B0BL6QL573