9 amp charge too fast for 25 Ah of LiFePo4?

[Crash Machine]

I have a Ping 48v 15 Ah battery in paralell with a 48v 10 AH Headway battery. These batteries have always been charged and discharged together and always reach full charge at the same time. The Headway I don't run with the BMS but I do have sense wires so I can balance charge every 5 to 10 charges. The Ping has the BMS hooked up as usual. I have been charging by hooking both my Ping 5 amp charger and my Soneil 3.5 amp into the paralell connectors of the batteries. Recently the 5 amp charger blew on me so I talked to Ping and he said he has a 9 amp charger. I only want the 9 amps charger for road trips. But is 9 amps too much of a charge for these batteries together? If I am charging through the discharge leads is that bypassing the Ping BMS? Thanks for any input you guys might have.

 

[dnmun]

what broke on the 5A charger?

why don't you charge using the regular charging connection? what prevents the pouches from overcharging?

we may be able to make your old charger work again, maybe.

 

[icecube57]

If you are charging two packs together they will be getting half the amperage each so it shoould be ok....

 

[dogman dan]

I would think so too. Same as a 5 amp charger on a 12 ah battery. I think the main limitation was the amps the bms could handle going in.

Anyway, if Ping says it's ok for the bms, it should be fine. The cells should be able to take a bit more than 5 amps.

 

[Crash Machine]

what broke on the 5A charger?

why don't you charge using the regular charging connection? what prevents the pouches from overcharging?

we may be able to make your old charger work again, maybe.

Unfortunately I broke the 5A charger . I was turning up the amperage and went too far. I tried 7 amps first and it seemed to handle it ok. Then I got greedy and went to 9 amps. It actually charged for about 20 minutes but then it blew quite dramatically.

When I am balance charging I do charge through the regular connection on the Ping battery at 3.5 amps. This charges both batteries they always come to full charge perfectly together and by running the BMS on the Headways occasionally they stay in balance perfectly. But when charging with both chargers I charge through the parallel connector beacause I am usually on a road trip and it is easier to get to. Really the only time I fast charge is on road trips. I just want to be able to have one charger to charge both batteries that I can carry just for fast charging on the road. Any other time I am in no hurry.

I have the charger apart already and got the board out without damaging it. I will post pics as soon as I can. But it is obvious what blew.

If you are charging two packs together they will be getting half the amperage each so it shoould be ok....

Thats what I was thinking. If they always discharge perfectly together then they should charge together just as well. I will order today and see how it all works. Thanks guys

 

[Punx0r]

If a 10Ah and 15Ah are charged in parallel and finish at the same time, the 15Ah will be taking 15/25 of the current. They'll each charge at the same C rate, though

I believe what you have there is a simple current divider, the current into each pack being determined by the internal resistance of each.

 

[dnmun]

i have one of the old 5A ping chargers if it is the same. i assume you blew up either the input power mosfets or the schottky diode. if you cannot read the part numbers then i can get them from mine or we can find a new mosfet or high speed diode schottky to fix it.

 

[Crash Machine]

i have one of the old 5A ping chargers if it is the same. i assume you blew up either the input power mosfets or the schottky diode. if you cannot read the part numbers then i can get them from mine or we can find a new mosfet or high speed diode schottky to fix it.

Wow thanks dnum. I just wrapped up school for the summer semester so I will have time to work on it. I went back to college for Electrical Engineering but I haven't gotten any hands on experience yet(first year). So I would love to fix this charger myself and learn what these parts look like and how to replace them. I gave it to a friend to look at. I will get it this afternoon and get some pics posted. Thanks again.

 

[dnmun]

i did the same thing. went back to college after working in biomedical research for few years. did not enjoy sacrificing animals. plus back then there were no jobs in biomed research. '73-74.

so i jumped directly into grad school in physics to study solid state, and ended up taking the junior and senior level courses in EE on the side while learning physics. had great EE teacher (he was a big head from Techtronics), but never used it for work since i got into the semiconductor manufacturing business after getting my masters.

i have used this place as way to learn the electronics i never really comprehended then. when you are a student it is all book learning. fixing stuff i like to do so fixing chargers is a good way to force yourself to examine the operation of the circuit. when i was home the last time i pulled out my old electronics textbook, by Millman, "digital electronics" is the title as i recall. it is all right there, emitter followers, common collector, class A, class B, amplifiers.

i had skipped circuits and just read the text and learned to analyze the circuits just from the textbook so it was difficult to go right into the junior and senior level electronics courses. learned to use SPICE and even built a abuncha projects using discrete and then complex ICs, like building op amps from parts, and autoranging DVMs. still have my breadboard projects in a box all these 35 years later.

you can read about how the Switch Mode Power Supplies work in some texts, but now the modern pwm IC controllers are a little different from the older TL494 type of pwm controller. the books are all dated, but i found for the newer type SMPS there was a white paper for the Everbright 816 opto used for feedback to the front end. that white paper is educational about how the newer ICs work like used in the headway charger, and the TI pdf on the TL494 is useful for understanding the older type of SMPS. heath knows a lot too. from experience.

 

[el_walto]

The Ping BMS is only rated for 5amps of charge, though i have charged my ping using my 6A charger from cell_man. Up to you, i guess it depends how hot the BMS gets.

 

[dnmun]

the current split is 60/40 so 60% of 9A is only 5.4A.

the charging mosfets get hot because they can spend a lot of time transitioning from on to off as the BMS shuts off for HVC, and while in the linear region and carrying a lot of current they can overheat. he is not charging thorugh the charging mosfet, he is charging through the output mosfets.

you can actually connect both the headway and the ping pack in parallel at each cell level so the entire double pack is paralleled at the cell level and then the ping can balance them at the same time, or you could use the headway BMS to balance them and disconnect the ping BMS sense wires when doing that. you can tie them in parallel with small cable, 24AWG would be fine imo.

it would be an interesting experiment. then see if the headway will balance the pack better than the ping and how much better.

but i worry that you might end up overcharging one of the cells if you don't have a BMS to protect it from overcharging during the charge.